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Aim: This study assessed the effects of hand‐bathing on sympathetic nervous activity exacerbated by psychological stress. Participants immersed one hand in warm water for 2 min while exposed to noise, and changes in blood flow and skin temperature of the non‐immersed hand were observed. Methods: Twenty‐nine healthy university students aged 20 years or older were randomly assigned to either the hand‐bathing group (n = 14) or the control group (n = 15). After a brief rest in a quiet environment, participants were exposed to noise for 6 min. Those in the hand‐bathing group submerged their left hand in a 40°C thermostatic bath for 2 min, starting 2 min into the noise exposure. The tympanic temperature, blood flow, and skin temperature of the non‐immersed hand were continuously measured, along with blood pressure and subjective evaluations before and after the noise exposure. Results: Both groups experienced a decrease in fingertip skin temperature at the start of the noise exposure, persisting longer in the control group. Conversely, the hand‐bathing group showed increased fingertip skin temperature after 150 s, significantly higher after the noise exposure than the control group (p =.04). Participants in the hand‐bathing group reported significantly increased overall body warmth, thermal comfort, and relaxation during hand‐bathing (p =.007, p =.01, p <.001). Conclusions: The 2‐min hand‐bathing intervention reversed the pronounced vasoconstrictive response induced by noise exposure and elicited heightened sensations of overall body warmth, thermal comfort, and relaxation. Hand‐bathing may mitigate heightened sympathetic nervous activity associated with psychological stress induced by noise exposure. [ABSTRACT FROM AUTHOR]

To determine whether using nicotine exacerbates exertional heat strain through an increased metabolic heat production (Hprod) or decreased skin blood flow (SkBF), 10 nicotine-naïve trained males [37 ± 12 yr; peak oxygen consumption (V̇ o 2peak): 66 ± 10 mL·min−1·kg−1] completed four trials at 20°C and 30°C following overnight transdermal nicotine (7 mg·24 h−1) and placebo use in a crossover, double-blind design. They cycled for 60 min (55% V̇ o 2peak) followed by a time trial (∼75% V̇ o 2peak) during which measures of gastrointestinal (Tgi) and mean weighted skin ( T ¯ sk) temperatures, SkBF, Hprod, and mean arterial pressure (MAP) were made. The difference in ΔTgi between nicotine and placebo trials was greater during 30°C (0.4 ± 0.5°C) than 20°C (0.1 ± 0.7°C), with T ¯ sk higher during nicotine than placebo trials (0.5 ± 0.5°C, P = 0.02). SkBF became progressively lower during nicotine than placebo trials (P = 0.01) and progressively higher during 30°C than 20°C trials (P < 0.01); MAP increased from baseline (P < 0.01) and remained elevated in all trials. The difference in Hprod between 30°C and 20°C trials was lower during nicotine than placebo (P = 0.01) and became progressively higher during 30°C than 20°C trials with exercise duration (P = 0.03). Mean power output during the time trial was lower during 30°C than 20°C trials (24 ± 25 W, P = 0.02), and although no effect of nicotine was observed (P > 0.59), two participants (20%) were unable to complete their 30°C nicotine trials as one reached the ethical limit for Tgi (40.0°C), whereas the other withdrew due to "nausea and chills" (Tgi = 39.7°C). These results demonstrate that nicotine use increases thermal strain and risk of exertional heat exhaustion by reducing SkBF. NEW & NOTEWORTHY: In naïve participants, acute nicotine use exerts a hyperthermic effect that increases the risk of heat exhaustion during exertional heat strain, which is driven by a blunted skin blood flow response. This has implications for 1) populations that face exertional heat strain and demonstrate high nicotine use (e.g., athletes and military, 25%–50%) and 2) study design whereby screening and exclusion for nicotine use or standardization of prior use (e.g., overnight abstinence) is encouraged. [ABSTRACT FROM AUTHOR]

Purpose: Cold-induced vasodilation (CIVD) is an oscillatory rise in blood flow to glabrous skin that occurs in cold-exposed extremities. Dietary flavanols increase bioavailable nitric oxide, a proposed mediator of CIVD through active vasodilation and/or withdrawal of sympathetic vascular smooth muscle tone. However, no studies have examined the effects of flavanol intake on extremity skin perfusion during cold exposure. We tested the hypothesis that acute and 8-day flavanol supplementation would augment CIVD during single-digit cold water immersion (CWI). Methods: Eleven healthy adults (24 ± 6 years; 10 M/1F) ingested cocoa flavanols (900 mg/day) or caffeine- and theobromine-matched placebo for 8 days in a double-blind, randomized, crossover design. On Days 1 and 8, CIVD was assessed 2 h post-treatment. Subjects immersed their 3rd finger in warm water (42 °C) for 15 min before CWI (4 °C) for 30 min, during which nail bed and finger pad skin temperature were measured. Results: Flavanol ingestion had no effect on CIVD frequency (Day 1, Flavanol: 3 ± 2 vs. Placebo: 3 ± 2; Day 8, Flavanol: 3 ± 2 vs. Placebo: 3 ± 1) or amplitude (Day 1, Flavanol: 4.3 ± 1.7 vs. Placebo: 4.9 ± 2.6 °C; Day 8, Flavanol: 3.9 ± 1.9 vs. Placebo: 3.9 ± 2.0 °C) in the finger pad following acute or 8-day supplementation (P > 0.05). Furthermore, average, nadir, and apex finger pad temperatures during CWI were not different between treatments on Days 1 or 8 of supplementation (P > 0.05). Similarly, no differences in CIVD parameters were observed in the nail bed following supplementation (P > 0.05). Conclusion: These data suggest that cocoa flavanol ingestion does not alter finger CIVD. Clinical Trial Registration Clinicaltrials.gov Identifier: NCT04359082. April 24, 2020. [ABSTRACT FROM AUTHOR]

Simple Summary: The following review is based on the use of infrared thermography as a method to assess stress-related autonomic activity and its association with cardiovascular and heart rate variability in domestic animals. Stress-induced hyperthermia is one of the main physiological responses of animals to a stressor. The increase in body temperature activates compensatory peripheral mechanisms to increase heat dissipation and prevent further temperature increases. Changes in skin blood flow cause alterations in cutaneous temperature, alterations that can be assessed through infrared thermography and that will be discussed in the present review. Most of the responses present in animals when exposed to stressors are mediated by the autonomic nervous system. The sympathetic nervous system, known as the one responsible for the "fight or flight" reaction, triggers cardiovascular changes such as tachycardia or vasomotor alterations to restore homeostasis. Increase in body temperature in stressed animals also activates peripheral compensatory mechanisms such as cutaneous vasodilation to increase heat exchange. Since changes in skin blood flow influence the amount of heat dissipation, infrared thermography is suggested as a tool that can detect said changes. The present review aims to analyze the application of infrared thermography as a method to assess stress-related autonomic activity, and their association with the cardiovascular and heart rate variability in domestic animals. [ABSTRACT FROM AUTHOR]

Synthetic progestins in oral contraceptives are thought to blunt heat dissipation by reducing skin blood flow and sweating. However, whether progestin‐releasing intrauterine devices (IUDs) modulate heat loss during exercise‐heat stress is unknown. We used direct calorimetry to measure whole‐body total (dry + evaporative) heat loss in young, physically active women (mean (SD); aged 24 (4) years, V̇O2peak${\dot V_{{{\mathrm{O}}_{\mathrm{2}}}{\mathrm{peak}}}}$ 39.3 (5.3) ml/kg/min) with (IUD; n = 19) and without (Control; n = 17) IUDs in the follicular and luteal phases of the menstrual cycle during light‐ and moderate‐intensity exercise at fixed rates of heat production (∼175 and ∼275 W/m2) in 30°C, ∼21% relative humidity. Between‐group and ‐phase differences were evaluated using traditional hypothesis testing and statistical equivalence testing within pre‐determined bounds (±11 W/m2; difference required to elicit a ±0.3°C difference in core temperature over 1 h) in each exercise bout. Whole‐body total heat loss was statistically equivalent between groups within ±11 W m−2 (IUD–Control [90% CIs]; Light: −2 [−8, 5] W/m2, P = 0.007; Moderate: 0 [−6, 6] W/m2, P = 0.002), as were dry and evaporative heat loss (P ≤ 0.023), except for evaporative heat loss during moderate‐intensity exercise (equivalence: P = 0.063, difference: P = 0.647). Whole‐body total and evaporative heat loss were not different between phases (P ≥ 0.267), but dry heat loss was 3 [95% CIs: 1, 5] W/m2 greater in the luteal phase (P ≤ 0.022). Despite this, all whole‐body heat loss outcomes were equivalent between phases (P ≤ 0.003). These findings expand our understanding of the factors that modulate heat exchange in women and provide valuable mechanistic insight of the role of endogenous and exogenous female sex hormones in thermoregulation. Key points: Progestin released by hormonal intrauterine devices (IUDs) may negatively impact heat dissipation during exercise by blunting skin blood flow and sweating. However, the influence of IUDs on thermoregulation has not previously been assessed.We used direct calorimetry to show that IUD users and non‐users display statistically equivalent whole‐body dry and evaporative heat loss, body heat storage and oesophageal temperature during moderate‐ and high‐intensity exercise in a warm, dry environment, indicating that IUDs do not appear to compromise exercise thermoregulation.However, within IUD users and non‐users, dry heat loss was increased and body heat storage and oesophageal temperature were reduced in the luteal compared to the follicular phase of the menstrual cycle, though these effects were small and unlikely to be practically meaningful.Together, these findings expand our understanding of the factors that modulate heat exchange in women and have important practical implications for the design of future studies of exercise thermoregulation. [ABSTRACT FROM AUTHOR]

In this, the second of four historical reviews on human thermoregulation during exercise, we examine the research techniques developed by our forebears. We emphasise calorimetry and thermometry, and measurements of vasomotor and sudomotor function. Since its first human use (1899), direct calorimetry has provided the foundation for modern respirometric methods for quantifying metabolic rate, and remains the most precise index of whole-body heat exchange and storage. Its alternative, biophysical modelling, relies upon many, often dubious assumptions. Thermometry, used for >300 y to assess deep-body temperatures, provides only an instantaneous snapshot of the thermal status of tissues in contact with any thermometer. Seemingly unbeknownst to some, thermal time delays at some surrogate sites preclude valid measurements during non-steady state conditions. To assess cutaneous blood flow, immersion plethysmography was introduced (1875), followed by strain-gauge plethysmography (1949) and then laser-Doppler velocimetry (1964). Those techniques allow only local flow measurements, which may not reflect whole-body blood flows. Sudomotor function has been estimated from body-mass losses since the 1600s, but using mass losses to assess evaporation rates requires precise measures of non-evaporated sweat, which are rarely obtained. Hygrometric methods provide data for local sweat rates, but not local evaporation rates, and most local sweat rates cannot be extrapolated to reflect whole-body sweating. The objective of these methodological overviews and critiques is to provide a deeper understanding of how modern measurement techniques were developed, their underlying assumptions, and the strengths and weaknesses of the measurements used for humans exercising and working in thermally challenging conditions. [ABSTRACT FROM AUTHOR]

Near‐infrared spectroscopy (NIRS) is used to measure tissue concentrations of oxyhemoglobin (O2Hb) and deoxyhemoglobin (HHb). In the context of exercise, NIRS confers a higher signal‐to‐noise ratio than other neuroimaging techniques. However, part of the signal may be influenced by thermoregulatory hyperemia in the superficial cutaneous capillaries of the forehead. The degree to which NIRS signals during exercise reflect cerebral or extracerebral hemodynamic changes is a continuing source of controversy. However, the influence of skin blood flow may be attenuated depending on the NIRS technique (e.g., frequency domain machines with maximal optode separation distances >3.5 cm). The purpose of this study was to compare the changes in forehead skin blood flow and cerebral hemoglobin concentration during incremental exercise versus direct vasodilation of the forehead skin induced by gradual local heating. Thirty participants (12 females, 18 males; age: 20.8 ± 3.2 years; body mass index: 23.8 ± 3.7 kg·m−2) participated in the study. Forehead skin blood flow was quantified laser Doppler flux and absolute concentrations of cerebral O2Hb and HHb were measured by NIRS. Local heating significantly increased the Doppler flux signal across time and these changes were significantly correlated with skin temperature. During incremental exercise, skin temperature, Doppler flux, O2Hb and HHb increased however, the only significant change that was consistently correlated with Doppler flux was skin temperature. Therefore, a significant change in forehead skin blood flow may not significantly the NIRS hemoglobin data, depending on the type of NIRS device used. [ABSTRACT FROM AUTHOR]

Most of the responses present in animals when exposed to stressors are mediated by the autonomic nervous system. The sympathetic nervous system, known as the one responsible for the “fight or flight” reaction, triggers cardiovascular changes such as tachycardia or vasomotor alterations to restore homeostasis. Increase in body temperature in stressed animals also activates peripheral compensatory mechanisms such as cutaneous vasodilation to increase heat exchange. Since changes in skin blood flow influence the amount of heat dissipation, infrared thermography is suggested as a tool that can detect said changes. The present review aims to analyze the application of infrared thermography as a method to assess stress-related autonomic activity, and their association with the cardiovascular and heart rate variability in domestic animals.

Integrative cardiovascular responses to heat stress during endurance exercise depend on various variables, such as thermal stress and exercise intensity. This review addresses how increases in skin temperature alter and challenge the integrative cardiovascular system during upright submaximal endurance exercise, especially when skin is hot (i.e. >38°C). Current evidence suggests that exercise intensity plays a significant role in cardiovascular responses to hot skin during exercise. At rest and during mild intensity exercise, hot skin increases skin blood flow and abolishes cutaneous venous tone, which causes blood pooling in the skin while having little impact on stroke volume and thus cardiac output is increased with an increase in heart rate. When the heart rate is at relatively low levels, small increases in heart rate, skin blood flow, and cutaneous venous volume do not compromise stroke volume, so cardiac output can increase to fulfill the demands for maintaining blood pressure, heat dissipation, and the exercising muscle. On the contrary, during more intense exercise, hot skin does not abolish exercise-induced cutaneous venoconstriction possibly due to high sympathetic nerve activities; thus, it does not cause blood pooling in the skin. However, hot skin reduces stroke volume, which is associated with a decrease in ventricular filling time caused by an increase in heart rate. When the heart rate is high during moderate or intense exercise, even a slight reduction in ventricular filling time lowers stroke volume. Cardiac output is therefore not elevated when skin is hot during moderate intensity exercise. [ABSTRACT FROM AUTHOR]

Hesperetin, a citrus flavonoid, exerts vasodilation and is expected to improve endothelial function and alleviate cold sensation by activating nervous system thermal transduction pathways. In this randomized, double-blind, crossover, and placebo-controlled study, the purpose was to assess the effect of an orally administered highly bioavailable soluble inclusion complex of hesperetine-7-O-glucoside with β-cyclodextrin (HEPT7G/βCD; SunActive® HES/HCD) on cold sensation response during localized cold-stimulated stress in healthy humans. A significant (p ≤ 0.05) dose-dependent increase in skin cutaneous blood flow following relatively small doses of HEPT7G/βCD inclusion complex ingestion was confirmed, which led to a relatively effective recovery of peripheral skin temperature. The time delay of an increase in blood flow during rewarming varied significantly between low- and high-dose HEPT7G/βCD inclusion complex consumption (e.g., 150 mg and 300 mg contain 19.5 mg and 39 mg of HEPT7G, respectively). In conclusion, the substantial alteration in peripheral skin blood flow observed during local cooling stress compared to placebo suggested that deconjugated hesperetin metabolites may have a distinct capacity for thermoregulatory control of human skin blood flow to maintain a constant body temperature during cold stress exposure via cutaneous vasodilation and vasoconstriction systems. [ABSTRACT FROM AUTHOR]

Exercise training has the potential for inducing enhancements in peripheral circulation, which can play important preventive and therapeutic roles in peripheral circulatory diseases. However, the relevant published studies show conflicting and inconclusive results. Furthermore, useful or optimum ambient temperature for this purpose has not yet been established. Therefore, we investigated the acute responses in peripheral circulation from exposure of healthy subjects to treadmill exercise under different ambient temperatures; A total of 12 young adult volunteers (males 6, females 6) randomly underwent three sessions of treadmill exercise for 30 min under three different ambient temperatures (10°C, 20°C, and 30°C), at a predetermined exercise intensity. Before and after the intervention, leg skin blood flow (SBF) was measured by laser Speckle flowgraphy and hand skin temperature (ST), by digital thermometry; After the cessation of treadmill exercise, compared to the corresponding baseline values, a significant increase in SBF was observed under all ambient temperature conditions (P [ J Adv Biotechnol Exp Ther 2023; 6(1.000): 222-230]

BackgroundAlterations in skin blood flow is a marker of inadequate tissue perfusion in critically ill patients after initial resuscitation. The effects of red blood cell transfusions (RBCT) on skin perfusion are not described in this setting. We evaluated the effects of red blood cell transfusions on skin tissue perfusion in critically ill patients without acute bleeding after initial resuscitation.MethodsA prospective observational study included 175 non-bleeding adult patients after fluid resuscitation requiring red blood cell transfusions. Using laser Doppler, we measured finger skin blood flow (SBF) at skin basal temperature (SBFBT), together with mean arterial pressure (MAP), heart rate (HR), hemoglobin (Hb), central venous pressure (CVP), lactate, and central or mixed venous oxygen saturation before and 1 h after RBCT. SBF responders were those with a 20% increase in SBFBT after RBCT.ResultsOverall, SBFBT did not significantly change after RBCT [from 79.8 (4.3–479.4) to 83.4 (4.9–561.6); p = 0.67]. A relative increase equal to or more than 20% in SBFBT after RBCT (SBF responders) was observed in 77/175 of RBCT (44%). SBF responders had significantly lower SBFBT [41.3 (4.3–279.3) vs. 136.3 (6.5–479.4) perfusion units; p

IntroductionLimited information is available on the biological effects of whole-body exposure to quasi-millimeter waves (qMMW). The aim of the present study was to determine the intensity of exposure to increase body temperature and investigate whether thermoregulation, including changes in skin blood flow, is induced in rats under whole-body exposure to qMMW.MethodsThe backs of conscious rats were extensively exposed to 28 GHz qMMW at absorbed power densities of 0, 122, and 237 W/m2 for 40 minutes. Temperature changes in three regions (dorsal and tail skin, and rectum) and blood flow in the dorsal and tail skin were measured simultaneously using fiber-optic probes.ResultsIntensity-dependent temperature increases were observed in the dorsal skin and the rectum. In addition, skin blood flow was altered in the tail but not in the dorsum, accompanied by an increase in rectal temperature and resulting in an increase in tail skin temperature.DiscussionThese findings suggest that whole-body exposure to qMMW drives thermoregulation to transport and dissipate heat generated on the exposed body surface. Despite the large differences in size and physiology between humans and rats, our findings may be helpful for discussing the operational health-effect thresholds in the standardization of international exposure guidelines.

Ultraviolet radiation (UVR) exposure acutely reduces nitric oxide (NO)-dependent cutaneous vasodilation. In addition, increased constitutive skin melanin is associated with attenuated NO-dependent cutaneous vasodilation. However, the impact of withinlimb variation in skin melanization, associated with seasonal UVR exposure, on NO-dependent cutaneous vasodilation is unknown. We investigated the effect of within-limb variation in skin melanin on NO-dependent cutaneous vasodilation. Intradermal microdialysis fibers were placed in the inner-upper arm, ventral forearm, and dorsal forearm of seven adults (33 ± 14 yr; 4 M/3 F) with constitutively light skin pigmentation. Melanin-index (M-index; an index of skin pigmentation), measured via reflectance spectrophotometry, confirmed differences in sun exposure among sites. A standardized local heating (42°C) protocol induced cutaneous vasodilation. After attaining a stable elevated blood flow plateau, 15 mM NG-nitro-L-arginine methyl ester (LNAME; NO synthase inhibitor) was infused to quantify the NO contribution. Laser-Doppler flowmetry (LDF) measured red cell flux and cutaneous vascular conductance (CVC = LDF/mean arterial pressure) and was normalized to maximal (%CVCmax; 28 mM sodium nitroprusside þ 43+C local heating). Dorsal forearm M-index was higher [50.5 ± 11.8 au (arbitrary units)] compared with the ventral forearm (37.5 ± 7.4 au; P ≤ 0.03) and upper arm (30.0 ± 4.0 au; P ≤ 0.001) M-index. Cutaneous vasodilation responses to local heating were not different among sites (P ≥ 0.12). Importantly, neither the magnitude of the local heating plateau (dorsal: 85 ± 21%; ventral: 70 ± 21%; upper: 87 ± 15%; P ≥ 0.16) nor the NO-mediated component of that response (dorsal: 59 ± 15%; ventral: 54 ± 13%; upper: 55 ± 11%; P ≥ 0.79) was different among sites. These data suggest that within-limb differences in skin pigmentation secondary to seasonal UVR exposure do not alter NO-dependent cutaneous vasodilation. [ABSTRACT FROM AUTHOR]

Spinal cord injury (SCI) causes a disruption of autonomic nervous regulation to the cardiovascular system, leading to various cardiovascular and microvascular diseases. Exercise training is an effective intervention for reducing risk for microvascular diseases in healthy people. However, the effectiveness of exercise training on improving microvascular function in people with SCI is largely unknown. The purpose of this study was to compare blood flow oscillations in people with spinal cord injury and different physical activity levels to determine if such a lifestyle might influence skin blood flow. A total of 37 participants were recruited for this study, including 12 athletes with SCI (ASCI), 9 participants with SCI and a sedentary lifestyle (SSCI), and 16 healthy able-bodied controls (AB). Sacral skin blood flow (SBF) in response to local heating at 42 °C for 50 min was measured using laser Doppler flowmetry. The degree of the regularity of blood flow oscillations (BFOs) was quantified using a multiscale entropy approach. The results showed that BFO was significantly more irregular in ASCI and AB compared to SSCI during the maximal vasodilation period. Our results also demonstrate that the difference in the regularity of BFOs between original SBF signal and phase-randomized surrogate time series was larger in ASCI and AB compared to SSCI. Our findings indicate that SCI causes a loss of complexity of BFOs and exercise training may improve complexity in people with SCI. This study demonstrates that multiscale entropy is a sensitive method for detecting differences between different categories of people with SCI and might be able to detect effects of exercise training related to skin blood flow. [ABSTRACT FROM AUTHOR]

Purpose: Vasoactive ingredients in beetroot (BR) such as nitrate are known to induce vasodilation in temperate conditions. This study investigated the effect of BR ingestion on cold induced vasodilation (CIVD) and rewarming of finger skin temperature (Tfing) during and after hand immersion in cold water. Methods: Twenty healthy males (mean ± SD; age 22.2 ± 0.7 years, height 172.6 ± 6.0 cm, body mass 61.3 ± 11.7 kg) repeated a hand cold water immersion test twice with prior BR or water beverage ingestion (randomised order). They rested for 2 h in thermoneutral conditions (27 °C, 40% relative humidity) after consuming the beverage, then immersed their non-dominant hand in 8 °C water for 30 min. They then rewarmed their hand in the ambient air for 20 min. Skin temperature at seven body sites, Tfing, finger skin blood flow (SkBFfing), and blood pressure were measured. Results: During hand immersion parameters of CIVD (Tfing and SkBFfing) were not different between BR and water conditions although skin temperature gradient from proximal to distal body sites was significantly smaller with BR (P < 0.05). During rewarming, SkBFfing and cutaneous vascular conductance were significantly higher with BR than with water (P < 0.05). The rewarming speed in Tfing and SkBFfing was significantly faster with BR at 15- (BR 1.24 ± 0.22 vs water 1.11 ± 0.26 °C/min) and 20-min rewarming (P < 0.05). Additionally, individuals with slower rewarming speed with water demonstrated accelerated rewarming with BR supplementation. Conclusion: BR accelerated rewarming in Tfing and SkBFfing after local cold stimulus, whereas, CIVD response during hand cold immersion was not affected by BR ingestion. [ABSTRACT FROM AUTHOR]

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Hesperetin, a citrus flavonoid, exerts vasodilation and is expected to improve endothelial function and alleviate cold sensation by activating nervous system thermal transduction pathways. In this randomized, double-blind, crossover, and placebo-controlled study, the purpose was to assess the effect of an orally administered highly bioavailable soluble inclusion complex of hesperetine-7-O-glucoside with β-cyclodextrin (HEPT7G/βCD; SunActive® HES/HCD) on cold sensation response during localized cold-stimulated stress in healthy humans. A significant (p ≤ 0.05) dose-dependent increase in skin cutaneous blood flow following relatively small doses of HEPT7G/βCD inclusion complex ingestion was confirmed, which led to a relatively effective recovery of peripheral skin temperature. The time delay of an increase in blood flow during rewarming varied significantly between low- and high-dose HEPT7G/βCD inclusion complex consumption (e.g., 150 mg and 300 mg contain 19.5 mg and 39 mg of HEPT7G, respectively). In conclusion, the substantial alteration in peripheral skin blood flow observed during local cooling stress compared to placebo suggested that deconjugated hesperetin metabolites may have a distinct capacity for thermoregulatory control of human skin blood flow to maintain a constant body temperature during cold stress exposure via cutaneous vasodilation and vasoconstriction systems.

The human body constantly exchanges heat with the environment. Temperature regulation is a homeostatic feedback control system that ensures deep body temperature is maintained within narrow limits despite wide variations in environmental conditions and activity-related elevations in metabolic heat production. Extensive research has been performed to study the physiological regulation of deep body temperature. This review focuses on healthy and disordered human temperature regulation during heat stress. Central to this discussion is the notion that various morphological features, intrinsic factors, diseases, and injuries independently and interactively influence deep body temperature during exercise and/or exposure to hot ambient temperatures. The first sections review fundamental aspects of the human heat stress response, including the biophysical principles governing heat balance and the autonomic control of heat loss thermoeffectors. Next, we discuss the effects of different intrinsic factors (morphology, heat adaptation, biological sex, and age), diseases (neurological, cardiovascular, metabolic, and genetic), and injuries (spinal cord injury, deep burns, and heat stroke), with emphasis on the mechanisms by which these factors enhance or disturb the regulation of deep body temperature during heat stress. We conclude with key unanswered questions in this field of research. [ABSTRACT FROM AUTHOR]

Wheelchair users have a higher risk of developing pressure ulcers due to prolonged seated pressure. Pressure ulcers can be painful, may require surgical intervention, and even become life-threatening if infection occurs. To prevent pressure ulcers from forming the patient must either offload themselves or rely on a caregiver to move them allowing pressure redistribution over the seated area. In this work, we designed a dynamic air cushion to relieve pressure on loaded areas using sequences of inflation and deflation of the air cushion cells. The purpose of these sequences is to offload pressure from high-risk areas. To evaluate the effect of the alternating sequences on seated pressure and blood perfusion, we recorded interface pressure, skin blood flow, superficial tissue oxygen saturation, blood concentrations of oxygenated hemoglobin, and deoxygenated hemoglobin from twenty-one healthy volunteers who were asked to sit on the air cushion for static mode recording (3 min) and during the inflation/deflation sequences (up to 22 min). The alternating sequences consisted of ten combined inflation and deflation steps. Results showed that, after applying the alternating sequences, interface pressure reduced significantly (p = 0.02) compared to the static mode. Moreover, the coefficient of variation of the seated pressure was higher (p < 0.001) during the alternation sequence compared to the static mode. However, interface pressure under the right and left ischial tuberosities increased (p < 0.001) during the alternation sequence compared to the static mode. In addition, during the alternating sequences, males had larger dispersion index values of both right and left ischial tuberosities pressure compared to females. Furthermore, the maximum value of oxygen saturation (p = 0.04) and skin blood flow (p = 0.001) increased during the pressure alternation sequences compared to the static mode. The study findings highlighted the positive effects of the designed dynamic air-cushion to relieve pressure on compressed areas and enhance blood perfusion similar to manual offloading approaches. The outcomes of this study are encouraging to evaluate the performance of the designed air cushion in studies involving wheelchair users. • Pressure alternation sequences resulted in a reduction of interface pressure. • Oxygen saturation and skin blood flow increased during the cushion zoned pressure alternation. • Dynamic air cushion was able of enhancing tissue blood perfusion and improving pressure distribution beneath the siting area. • Males had larger pressure dispersion values of both right and left ischial tuberosities compared to females. [ABSTRACT FROM AUTHOR]

Intermittent pneumatic compression (IPC) is commonly used to improve peripheral circulation of the lower extremity. However, its therapeutic dosage for people with type 2 diabetes mellitus (DM) at risk for ulcers is not well established. This study explored the effect of IPC with different inflation pressures on the distal microvascular responses of the foot in people with type 2 DM. Twenty‐four subjects with and without DM were recruited. Three IPC protocols with inflation pressures of 60, 90, and 120 mmHg were applied to the foot. The foot skin blood flow (SBF) responses were measured by laser Doppler flowmetry during and after IPC interventions. Results show that all three IPC interventions significantly increased foot SBF of IPC stage in healthy subjects, but only 90 and 120 mmHg IPC significantly improved SBF in diabetic subjects. IPC with 90 and 120 mmHg showed a greater effect than 60 mmHg in both groups, but 120 mmHg IPC was more effective for diabetic subjects. This study demonstrates that 90 and 120 mmHg are effective dosages of IPC for improving blood flow in healthy people, and 120 mmHg IPC may be more suitable for people with type 2 DM. [ABSTRACT FROM AUTHOR]

Human cutaneous microdialysis approaches for assessing nitric oxide (NO)-dependent blood flow include local heating (LH) of the skin until a plateau is reached, followed by infusion of a NO synthase inhibitor such as L-NAME; however, varied methods of quantifying and expressing NO-dependent vasodilation can obfuscate data interpretation and reproducibility. We retrospectively assessed NO-dependent vasodilation during LH to 39°C or 42°C, calculated as the: (1) absolute contribution of the NO-dependent component (along with baseline and the non-NO-dependent component) to the total cutaneous vascular conductance (CVC) response to LH, normalized to maximal CVC (%CVC max ); (2) difference in %CVC max (∆%CVC max ) between the LH plateau and post-NO inhibition (L-NAME plateau; ∆%CVC max =LH plateau-L-NAME plateau); (3) percentage of the LH plateau attributable to ∆%CVC max (%Plateau = ∆%CVC max /LH plateau*100); and (4) %Plateau when correcting for baseline. The LH plateaus during 39°C and 42°C were 48±17 %CVC max (9±5% baseline; 2±4% non-NO-dependent; 36±15% NO-dependent) and 88±10 %CVC max (15±8% baseline; 9±10% non-NO-dependent; 64±13% NO-dependent), respectively. The absolute contributions of the non-NO-dependent and NO-dependent components of the response (p<0.0001) and the ∆%CVC max (66±14% vs. 38±15%) were greater during 42°C compared with 39°C (all p≤0.02); however, there were no differences between the two protocols in %Plateau (75±13% vs. 80±10%; p=0.57) or %Plateau BL (88±14% vs. 95±8%; p=0.31). For both protocols, the values were greater for %Plateau BL versus ∆%CVC max and %Plateau (p≤0.0001), and for %Plateau versus ∆%CVC max (p≤0.05). Quantification of NO-dependent skin vasodilation responses to LH is dependent upon the mathematical approach and verbal description, which can meaningfully impact data interpretation and reproducibility.

Background: The objective of this study was to investigate the differences in skin blood flow regulations between the upper and lower limbs in healthy adults using wavelet analysis of skin blood oscillations. To the best of our knowledge, this is the first study investigating the dominant skin blood flow control of the upper and lower limbs in healthy adults., Methods: Skin blood flow of the forearm and leg was simultaneously measured by laser Doppler flowmetry (LDF) in 17 healthy adults. Skin blood flow oscillations were analyzed using wavelet analysis to assess the dominant control among the metabolic endothelial (0.0095-0.02 Hz), neurogenic (0.02-0.05 Hz), myogenic (0.05-0.15 Hz), respiratory (0.15-0.4 Hz), and cardiac (0.4-2 Hz) origins., Results: Skin blood flow in the leg (11.13 ± 4.90 perfusion unit) was significantly higher than in the forearm (6.90 ± 2.50 perfusion unit, p < 0.001). The metabolic endothelial control is more dominant in the forearm (1.19 ±0.51 au) compared to the leg (0.73 ± 0.41 au, p < 0.01). The myogenic control is more dominant in the leg (1.18 ± 0.28 au) compared to the forearm (0.96±0.18 au, p < 0.05)., Conclusion: Through wavelet analysis of skin blood flow oscillations, the results indicate that metabolic endothelial control is more dominant in the forearm (upper limbs) and myogenic control is more dominant in the leg (lower limbs)., (© 2024 The Author(s). Skin Research and Technology published by John Wiley & Sons Ltd.)

The purpose of this study was to clarify the effect of aerobic exercise training on the coldness of the body and physiologically-related factors in Japanese young women with cold constitution. Eighteen subjects were divided into two groups: exercise (E) and non-exercise control (C) groups. Subjects in the E group performed exercise training of fast walking 4 days or more per week for 4 weeks. The training significantly decreased the scores for cold feeling in the fingertips and toes, but did not change the metabolic rate or sublingual and skin temperatures in the hands and feet during rest under normothermic conditions. In the C group, all variables remained unchanged throughout the 4-week control period. These results suggest that aerobic exercise mitigated coldness in the distal portion of the extremities via the reduction of cold sensation at a normal body temperature in young women complaining of chilliness.

Remote ischaemic preconditioning (RIPC), induced by intermittent periods of limb ischaemia and reperfusion, confers cardiac and vascular protection from subsequent ischaemia–reperfusion (IR) injury. Early animal studies reliably demonstrate that RIPC attenuated infarct size and preserved cardiac tissue. However, translating these adaptations to clinical practice in humans has been challenging. Large clinical studies have found inconsistent results with respect to RIPC eliciting IR injury protection or improving clinical outcomes. Follow‐up studies have implicated several factors that potentially affect the efficacy of RIPC in humans such as age, fitness, frequency, disease state and interactions with medications. Thus, realizing the clinical potential for RIPC may require a human experimental model where confounding factors are more effectively controlled and underlying mechanisms can be further elucidated. In this review, we highlight recent experimental findings in the peripheral circulation that have added valuable insight on the mechanisms and clinical benefit of RIPC in humans. Central to this discussion is the critical role of timing (i.e. immediate vs. delayed effects following a single bout of RIPC) and the frequency of RIPC. Limited evidence in humans has demonstrated that repeated bouts of RIPC over several days uniquely improves vascular function beyond that observed with a single bout alone. Since changes in resistance vessel and microvascular function often precede symptoms and diagnosis of cardiovascular disease, repeated bouts of RIPC may be promising as a preclinical intervention to prevent or delay cardiovascular disease progression. [ABSTRACT FROM AUTHOR]

Cutaneous microcirculatory perfusion is commonly measured using laser Doppler flowmetry (LDF) probes, which provide a continuous, non-invasive quantification of skin blood flow (SkBF). However, inhomogeneities in the skin's microvasculature density contribute to a decrease in reproducibility whenever an LDF probe is removed and replaced, as is the case during pre- and post-intervention or between-day measurements. Therefore, this study aimed to determine whether increasing the total number of individual LDF probes in a localized area improves the reproducibility of the measurement. Seven laser Doppler probes were secured in a custom-made acrylic holder designed to attach to the skin's surface easily. SkBF, local skin temperature (Tsk), and blood pressure (BP) were assessed in 11 participants (6 M, 5 F, 42 ± 15 years). SkBF and Tsk were measured from the dorsal forearm (arm trial) for 5 min. Next, the multi-laser device was moved to the lateral side of the calf (leg trial), and measurements were obtained for 5 min. Each arm and leg trial was cyclically repeated three times, and all trials were separated by intermissions lasting 10–15 min. The average SkBF and the cutaneous vascular conductance (CVC) from all possible LDF probe combinations were not statistically different across the three arm and leg trials. Two-way mixed-effects models with absolute agreement were used to compute the intraclass correlation coefficient (ICC) for CVC, and the minimum ICC increased with the addition of LDF probes. The ICC of the average CVC from seven LDF probes was 0.96 between the arm trials and 0.91 between the leg trials, which suggests that there is excellent reliability and little difference between trials following the removal and replacement of the device. Moreover, all individual ICC values from ≥3 LDF probe combinations were greater than 0.70 (i.e., good reliability). These data suggest that SkBF measurements with multiple laser Doppler probes in a custom-made holder have excellent reproducibility after replacing the probes within the same participant. Therefore, this application could provide more reproducible assessments between repeated measurements (e.g., before and after exercise or clinical procedures) where the LDF probes must be removed and replaced within the same location. [ABSTRACT FROM AUTHOR]

Cutaneous microcirculatory perfusion is commonly measured using laser Doppler flowmetry (LDF) probes, which provide a continuous, non-invasive quantification of skin blood flow (SkBF). However, inhomogeneities in the skin’s microvasculature density contribute to a decrease in reproducibility whenever an LDF probe is removed and replaced, as is the case during pre- and post-intervention or between-day measurements. Therefore, this study aimed to determine whether increasing the total number of individual LDF probes in a localized area improves the reproducibility of the measurement. Seven laser Doppler probes were secured in a custom-made acrylic holder designed to attach to the skin’s surface easily. SkBF, local skin temperature (Tsk), and blood pressure (BP) were assessed in 11 participants (6 M, 5 F, 42 ± 15 years). SkBF and Tsk were measured from the dorsal forearm (arm trial) for 5 min. Next, the multi-laser device was moved to the lateral side of the calf (leg trial), and measurements were obtained for 5 min. Each arm and leg trial was cyclically repeated three times, and all trials were separated by intermissions lasting 10–15 min. The average SkBF and the cutaneous vascular conductance (CVC) from all possible LDF probe combinations were not statistically different across the three arm and leg trials. Two-way mixed-effects models with absolute agreement were used to compute the intraclass correlation coefficient (ICC) for CVC, and the minimum ICC increased with the addition of LDF probes. The ICC of the average CVC from seven LDF probes was 0.96 between the arm trials and 0.91 between the leg trials, which suggests that there is excellent reliability and little difference between trials following the removal and replacement of the device. Moreover, all individual ICC values from ≥3 LDF probe combinations were greater than 0.70 (i.e., good reliability). These data suggest that SkBF measurements with multiple laser Doppler probes in a custom-made holder have excellent reproducibility after replacing the probes within the same participant. Therefore, this application could provide more reproducible assessments between repeated measurements (e.g., before and after exercise or clinical procedures) where the LDF probes must be removed and replaced within the same location.

Spinal cord injury (SCI) causes a disruption of autonomic nervous regulation to the cardiovascular system, leading to various cardiovascular and microvascular diseases. Exercise training is an effective intervention for reducing risk for microvascular diseases in healthy people. However, the effectiveness of exercise training on improving microvascular function in people with SCI is largely unknown. The purpose of this study was to compare blood flow oscillations in people with spinal cord injury and different physical activity levels to determine if such a lifestyle might influence skin blood flow. A total of 37 participants were recruited for this study, including 12 athletes with SCI (ASCI), 9 participants with SCI and a sedentary lifestyle (SSCI), and 16 healthy able-bodied controls (AB). Sacral skin blood flow (SBF) in response to local heating at 42 °C for 50 min was measured using laser Doppler flowmetry. The degree of the regularity of blood flow oscillations (BFOs) was quantified using a multiscale entropy approach. The results showed that BFO was significantly more irregular in ASCI and AB compared to SSCI during the maximal vasodilation period. Our results also demonstrate that the difference in the regularity of BFOs between original SBF signal and phase-randomized surrogate time series was larger in ASCI and AB compared to SSCI. Our findings indicate that SCI causes a loss of complexity of BFOs and exercise training may improve complexity in people with SCI. This study demonstrates that multiscale entropy is a sensitive method for detecting differences between different categories of people with SCI and might be able to detect effects of exercise training related to skin blood flow.

The objective of this study was 1) to examine pooled effects of hypertension on nitric oxide (NO)-dependent vasodilation during local heating across multiple nonglabrous skin regions, and 2) explore regional differences. Responses were compared between 14 participants with uncomplicated hypertension controlled with medication (7 females, 61 ± 6 yr) and 14 age-matched nonhypertensive controls (6 females; 60 ± 5 yr). Cutaneous vascular conductance, normalized to maximum vasodilation (%CVCmax), was assessed at the upper chest, abdomen, dorsal forearm, thigh, and lateral calf during local heating. Across all regions, local skin temperatures were simultaneously increased from 33°C to 42°C (1°C·10 s-1) and held until a stable heating plateau was achieved (~40 min), followed by continuous infusion of 20 mM of NG-nitro-l-arginine methyl ester (l-NAME; ~40 min) at all sites until a stable l-NAME plateau was achieved. The difference between heating and l-NAME plateaus was defined as the NO-contribution. Statistical equivalence for each heating phase was determined based on equivalence bounds of ±10%CVCmax for between-group differences. Pooled (all-regions) %CVCmax responses were equivalent for baseline (two one-sided t tests; P < 0.001), heating plateau (P = 0.002), l-NAME plateau (P = 0.028), and NO-contribution (P = 0.003). For individual regions, responses were equivalent at baseline for the abdomen, thigh, and calf, the heating plateau for the thigh, and the l-NAME plateau for the calf (all P < 0.05). Conversely, the calf heating plateau was lower in the hypertension group (t test; P < 0.05). Local heat-induced cutaneous vasodilation was statistically equivalent between individuals with uncomplicated, controlled hypertension, and nonhypertensive age-matched adults when pooled across multiple skin sites. Conversely, individual between-region comparisons were generally too variable to permit definitive conclusions. [ABSTRACT FROM AUTHOR]

The optimal frequency and duration of remote ischemic preconditioning (RIPC) that augments microvascular function is unknown. A single bout of RIPC increases cutaneous endothelial function for ∼48 h, whereas 1 week of daily RIPC bouts improves more sustained endothelium-independent function. We hypothesized that 3 days of RIPC separated by rest days (3QOD RIPC) would result in sustained increases in both endothelium-dependent and endothelium-independent functions. Cutaneous microvascular function was assessed in 13 healthy young participants (aged 20.5 ± 3.9 years; 5 males, 8 females) before 3QOD and then 24, 48, and 72 h and a week after 3QOD. RIPC consisted of four repetitions of 5 min of blood flow occlusion separated by 5 min of reperfusion. Skin blood flow responses to local heating (T loc = 42°C), acetylcholine (Ach), and sodium nitroprusside (SNP) were measured using laser speckle contrast imaging and expressed as cutaneous vascular conductance (CVC = PU⋅mmHg–1). Local heating-mediated vasodilation was increased 72 h after 3QOD and the increased responsivity persisted a week later (1.08 ± 0.24 vs. 1.34 ± 0.46, 1.21 ± 0.36 PU⋅mmHg–1; ΔCVC, pre-RIPC vs. 72 h, a week after 3QOD; P = 0.054). Ach-induced cutaneous vasodilation increased a week after 3QOD (0.73 ± 0.41 vs. 0.95 ± 0.49 PU⋅mmHg–1; ΔCVC, pre-RIPC vs. a week after 3QOD; P < 0.05). SNP-induced cutaneous vasodilation increased 24 h after 3QOD (0.47 ± 0.28 vs. 0.63 ± 0.35 PU⋅mmHg–1; ΔCVC, pre-RIPC vs. 24 h; P < 0.05), but this change did not persist thereafter. Thus, 3QOD induced sustained improvement in endothelium-dependent vasodilation but was not sufficient to sustain increases in endothelium-independent vasodilation. [ABSTRACT FROM AUTHOR]

Objective: Thoracic outlet syndrome (TOS) should be considered of arterial origin only if patients have clinical symptoms that are the result of documented symptomatic ischemia. Simultaneous recording of inflow impairment and forearm ischemia in patients with suspected TOS has never been reported to date. We hypothesized that ischemia would occur in cases of severely impaired inflow, resulting in a non-linear relationship between changes in pulse amplitude (PA) and the estimation of ischemia during provocative attitudinal upper limb positioning. Design: Prospective single center interventional study. Material: Fifty-five patients with suspected thoracic outlet syndrome. Methods: We measured the minimal decrease from rest of transcutaneous oximetry pressure (DROPm) as an estimation of oxygen deficit and arterial pulse photo-plethysmography to measure pulse amplitude changes from rest (PA-change) on both arms during the candlestick phase of a "Ca + Pra" maneuver. "Ca + Pra" is a modified Roos test allowing the estimation of maximal PA-change during the "Pra" phase. We compared the DROPm values between deciles of PA-changes with ANOVA. We then analyzed the relationship between mean PA-change and mean DROPm of each decile with linear and second-degree polynomial (non-linear) models. Results are reported as median [25/75 centiles]. Statistical significance was p < 0.05. Results: DROPm values ranged −11.5 [−22.9/−7.2] and − 12.3 [−23.3/−7.4] mmHg and PA-change ranged 36.4 [4.6/63.8]% and 38.4 [−2.0/62.1]% in the right and left forearms, respectively. The coefficient of determination between median DROPm and median PA-change was r 2 = 0.922 with a second-degree polynomial fitting, but only r 2 = 0.847 with a linear approach. Conclusion: Oxygen availability was decreased in cases of severe but not moderate attitudinal inflow impairments. Undertaking simultaneous A-PPG and forearm oximetry during the "Ca + Pra" maneuver is an interesting approach for providing objective proof of ischemia in patients with symptoms of TOS suspected of arterial origin. [ABSTRACT FROM AUTHOR]

Vascular dysfunction has been reported in adults who have recovered from COVID-19. To date, no studies have investigated the underlying mechanisms of persistent COVID-19-associated vascular dysfunction. Our purpose was to quantify nitric oxide (NO)-mediated vasodilation in healthy adults who have recovered from SARS-CoV-2 infection. We hypothesized that COVID-19-recovered adults would have impaired NO-mediated vasodilation compared with adults who have not had COVID-19. In methods, we performed a cross-sectional study including 10 (5 men/5 women, 24 ± 4 yr) healthy control (HC) adults who were unvaccinated for COVID-19, 11 (4 men/7 women, 25 ± 6 yr) healthy vaccinated (HV) adults, and 12 (5 men/7 women, 22 ± 3 yr) post-COVID-19 (PC, 19 ± 14 wk) adults. COVID-19 symptoms severity (survey) was assessed. A standardized 39°C local heating protocol was used to assess NO-dependent vasodilation via perfusion (intradermal microdialysis) of 15 mM NG-nitro-l-arginine methyl ester during the plateau of the heating response. Red blood cell flux was measured (laser-Doppler flowmetry) and cutaneous vascular conductance (CVC = flux/mmHg) was expressed as a percentage of maximum (28 mM sodium nitroprusside + 43°C). In results, the local heating plateau (HC: 61 ± 20%, HV: 60 ± 19%, PC: 67 ± 19%, P = 0.80) and NO-dependent vasodilation (HC: 77 ± 9%, HV: 71 ± 7%, PC: 70 ± 10%, P = 0.36) were not different among groups. Neither symptom severity (25 ± 12 AU) nor time since diagnosis correlated with the NO-dependent vasodilation (r = 0.46, P = 0.13; r = 0.41, P = 0.19, respectively). In conclusion, healthy adults who have had mild-to-moderate COVID-19 do not have altered NO-mediated cutaneous microvascular function. NEW & NOTEWORTHY Healthy young adults who have had mild-to-moderate COVID-19 do not display alterations in nitric oxide-mediated cutaneous microvascular function. In addition, healthy young adults who have COVID-19 antibodies from the COVID-19 vaccinations do not display alterations in nitric oxide-mediated cutaneous microvascular function. [ABSTRACT FROM AUTHOR]

Global warming, provoked by the greenhouse effect of high levels of atmospheric gases (most notably carbon dioxide and methane), directly threatens human health and survival. Individuals vary in their capacity to tolerate episodes of extreme heat. Because skin is the organ tasked with heat dissipation, it is important for dermatologists to be versed in the physiology of cutaneous heat dissipation and cognizant of clinical settings in which the skin’s thermoregulatory responses may be impaired. When the external temperature is lower than that of the skin, the skin releases internal heat through direct thermal exchange with the environment, a process that is aided by an expansion of cutaneous blood flow and eccrine sweating. Cooling through the evaporation of sweat is effective even when the external temperature exceeds that of skin. Many factors, including environmental and physiological (e.g., age and sex), and pathological (e.g., preexisting illnesses, disorders of eccrine function, and medications) considerations, affect the skin’s capacity to thermoregulate. Identification of individuals at increased risk for heat-related morbidity and mortality will become increasingly important in the care of patients.

The optimal frequency and duration of remote ischemic preconditioning (RIPC) that augments microvascular function is unknown. A single bout of RIPC increases cutaneous endothelial function for ∼48 h, whereas 1 week of daily RIPC bouts improves more sustained endothelium-independent function. We hypothesized that 3 days of RIPC separated by rest days (3QOD RIPC) would result in sustained increases in both endothelium-dependent and endothelium-independent functions. Cutaneous microvascular function was assessed in 13 healthy young participants (aged 20.5 ± 3.9 years; 5 males, 8 females) before 3QOD and then 24, 48, and 72 h and a week after 3QOD. RIPC consisted of four repetitions of 5 min of blood flow occlusion separated by 5 min of reperfusion. Skin blood flow responses to local heating (Tloc = 42°C), acetylcholine (Ach), and sodium nitroprusside (SNP) were measured using laser speckle contrast imaging and expressed as cutaneous vascular conductance (CVC = PU⋅mmHg–1). Local heating-mediated vasodilation was increased 72 h after 3QOD and the increased responsivity persisted a week later (1.08 ± 0.24 vs. 1.34 ± 0.46, 1.21 ± 0.36 PU⋅mmHg–1; ΔCVC, pre-RIPC vs. 72 h, a week after 3QOD; P = 0.054). Ach-induced cutaneous vasodilation increased a week after 3QOD (0.73 ± 0.41 vs. 0.95 ± 0.49 PU⋅mmHg–1; ΔCVC, pre-RIPC vs. a week after 3QOD; P < 0.05). SNP-induced cutaneous vasodilation increased 24 h after 3QOD (0.47 ± 0.28 vs. 0.63 ± 0.35 PU⋅mmHg–1; ΔCVC, pre-RIPC vs. 24 h; P < 0.05), but this change did not persist thereafter. Thus, 3QOD induced sustained improvement in endothelium-dependent vasodilation but was not sufficient to sustain increases in endothelium-independent vasodilation.

Objectives: To assess microvascular reactivity during a skin thermal challenge early post-cardiac surgery and its association with outcomes., Design: Noninvasive physiological study., Setting: Thirty-five-bed department of intensive care., Participants: Patients admitted to the intensive care unit post-cardiac surgery., Interventions: Thermal challenge., Measurements and Main Results: A total of 46 patients were included; 14 needed vasoactive or ventilatory support for at least 48 hours (slow recovery), and 32 had a more rapid recovery. Skin blood flow (SBF) was measured on the anterior proximal forearm using skin laser Doppler. A thermal challenge was performed by abruptly increasing local skin temperature from 37°C to 43°C while monitoring SBF. The ratio between SBFs at 43°C and 37°C was calculated to measure microvascular reactivity. SBF at 37°C was not significantly different in patients with a slow recovery and those with a rapid recovery, but SBF after 9 minutes at 43°C was lower (48.5 [17.3-69.0] v 85.1 [45.2-125.7], p < 0.01), resulting in a lower SBF ratio (2.8 [1.5-4.7] v 4.8 [3.7-7.8], p < 0.01). Patients with lower SBF ratios were more likely to have dysfunction of at least one organ (assessed using the sequential organ dysfunction score) 48 hours post-cardiac surgery than those with higher ratios: 88% versus 40% versus 27% (p < 0.01), respectively, for the lowest, middle, and highest tertiles of SBF ratio. In multivariable analysis, a lower SBF ratio was an independent risk factor for slow recovery., Conclusions: Early alterations in microvascular reactivity, evaluated by a skin thermal challenge, are correlated with organ dysfunction. These observations may help in the development of new, simple, noninvasive monitoring systems in postoperative patients., Competing Interests: Declaration of competing interest The authors declare no conflicts of interest related to this manuscript., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Heat accumulation from wearing personal protective equipment can result in the development of heat-related illnesses. This study aimed to investigate factors of heat stress with and without a US standard issue wildland firefighter helmet. Ten male subjects finished a 90-min exercise protocol in a heat chamber (358C and 30% relative humidity), with standard issue meta-aramid shirt and pants and a cotton t-shirt, and either with or without a wildland firefighter helmet. A randomised crossover design was implemented, with a minimum 2-week washout period. Heart rate, physiologic strain index, perceived head heat, head heat and skin blood flow of the head and neck were measured. At the conclusion of the 90-min trial, heart rate, physiological strain index, core temperature, rating of perceived exertion and perceived head heat showed a main effect of time (P,0.05). Perceived head heat and head heat exhibited a main effect of trial (P,0.05). The change in physiologic strain was positively correlated with the change in skin blood flow of the head (r = 0.72, P = 0.02). These data suggest that the current wildland firefighter helmet contributes to heat accumulation. The design of the wildland firefighter helmet lacks ventilation, which, from these data, may result in metabolic alterations and perceived discomfort. [ABSTRACT FROM AUTHOR]

Physical activity has been recommended by the American Diabetes Association (ADA) as a preventive intervention of diabetes complications. However, there is no study investigating how microvascular control mechanism respond to different walking intensities in people with and without diabetes. The purpose of this study was to assess microvascular control mechanism of the plantar foot in response to various walking speeds and durations in 12 healthy people using spectral analysis of skin blood flow (SBF) oscillations. A 3×2 factorial design, including 3 speeds (3, 6, and 9 km/h) and 2 durations (10 and 20 minutes), was used in this study. Plantar SBF was measured using laser Doppler flowmetry over the first metatarsal head. Borg Rating of Perceived Exertion (RPE) scale and heart rate maximum were used to assess the walking intensity. Wavelet analysis was used to quantify regulations of metabolic (0.0095-0.02 Hz), neurogenic (0.02-0.05 Hz), myogenic (0.05-0.15 Hz), respiratory (0.15-0.4 Hz), and cardiac (0.4-2 Hz) controls. For 10-minute walking, walking at 9 km/h significantly increased the ratio of wavelet amplitudes of metabolic, neurogenic, myogenic, respiratory, and cardiac mechanisms compared with 3 km/h (P <.05). For 20-minute walking, walking at 6 km/h significantly increased the ratio of wavelet amplitudes of metabolic, myogenic, respiratory, and cardiac compared with 3 km/h (P <.05). RPE showed a significant interaction between the speed and duration factors (P <.01). This is the first study demonstrating that different walking speeds and durations caused different plantar microvascular regulations. [ABSTRACT FROM AUTHOR]

Pressure Ulcers (PUs) are localized tissue damage that usually occur over the soft tissue of body prominence when a subject is exposed to prolonged external mechanical loading. Several studies have proposed that skin blood flow response (SBFR) can be used in PU evaluation to determine tissue ischemic accumulation due to insufficient time of tissue recovery. In previous study, twenty one Sprague Dawley rats weigh 388-481g that were divided into three different group have been used to investigate the trends of SBFR signal using time domain features like peak reactive hyperaemia (RH), time to peak RH and area under the RH curve as well as frequency domain features like peak power spectral density (PSD) and total PSD. However, the results indicate that both frequency domain features are not effective at determining individual insufficient recovery time. In this study, Continuous Wavelet Transform (CWT) based features such as average amplitude and relative amplitude based on Morlet wavelet function scale 200 are investigated. The results show that the samples representing inconsistent trend of average amplitude for metabolic frequency range are dominant in all short (3 samples) , moderate (4 samples) and prolonged groups (4 samples), while no clear pattern can be established for relative amplitude. Hence both features may not suitable at distinguishing between sufficient and insufficient recovery time due to the low percentage in number of samples.

Abstract Background This study examined the effects of immersion in stirred, high-concentration, artificial carbonic acid water on body cooling. Methods Seven healthy male students (23 ± 2 years old) participated in the experiment. Signed informed consent was obtained from all subjects before the experiment. The subjects changed into shorts and T-shirts and entered an experimental room (with room temperature controlled at 30 °C and relative humidity maintained at 70%) at least 30 min before starting the experiment. After starting the experiment, the subjects were asked to rest on an exercise bike for 5 min and then pedal for 20 min. The exercise load was set to reach 50% of each subject’s presumed maximum oxygen intake at 5 min after starting exercise. Subjects then continued pedaling for 1 min to cool down. After this exercise, subjects sat on a chair and immersed forearms in tap water or artificial carbonic acid water (CO2 water) at 25 °C for 20 min. During immersion, tap water or CO2 water was stirred slowly with a pump. After immersion, subjects rested for 10 min. Skin temperature and skin blood flow (left forearm), as well as heart rate and ear canal temperature, were measured continuously. Thermal sensation and thermal comfort were measured intermittently. Results Skin blood flow of the immersed forearms was higher in CO2 water than in tap water during immersion. The blood flow in the last 5 min (average at rest was 100%) was significantly higher in CO2 water (290.85 ± 84.81%) than in tap water (104.80 ± 21.99%). Thermal sensation and thermal comfort were not different between conditions. Ear canal temperature significantly declined more in CO2 water (− 0.56 ± 0.31 °C) than in tap water (− 0.48 ± 0.30 °C) during immersion. Conclusions Our study suggests that immersion of the forearms in slowly stirred CO2 water at 25 °C reduces core temperature elevated by heat stress or exercise more effectively than does tap water at the same temperature. Immersion of the forearms in stirred CO2 water at 25 °C could be useful as a preventive measure against heat stroke from summer work or exercise.

The focus of this study is to model the cardiovascular system (CS) involving regional skin blood flow (SBF) to gain new insights into the skin-CS relationship. A lumped parameter model with a series of electrical components was developed to model the CS involving SBF. Four parts were considered: the heart, arterial circulation, microcirculation (including the skin and other tissues), and the venous system. The model was validated based on previous publications. Additionally, the body surface was divided into seven blocks replaced by lumped resistances in this model, including the head, upper limbs and neck, chest and back, anterolateral abdomen, posterior abdomen, lower limbs, and buttocks. The SBF of each block was described using a weighted average method (relative ratio of cutaneous blood perfusion and regional body surface area) Cardiodynamics characterized the properties of cardiac cycles, including isovolumic contraction, accelerated ejection, decelerated ejection, isovolumic diastole, and filling phases. Blood flow and pulse pressure in the arterial trunk declined and increased, respectively, from the aorta root to the distal portion, exhibiting normal cardiovascular properties. Accordingly, the blood pressure of the arterial branches attached to the arterial trunk also satisfied normal physiological characteristics; the blood flow of all the arterial branches exhibited good agreement with previous studies. Additionally, the modeled SBF of each region was consistent with the data from the weighted average method. This model effectively demonstrates the normal properties of the CS that involves regional SBF and may be promising in the prediction of the skin-CS relationship. [ABSTRACT FROM AUTHOR]

To assess the impact of acute caffeine ingestion on thermoregulatory responses during steady-state exercise under moderate heat stress conditions in caffeine-habituated and nonhabituated individuals. Twenty-eight participants [14 habituated (HAB) (4 females) and 14 nonhabituated (NHAB) (6 females)] cycled at a fixed metabolic heat production (7 W·kg-1) for 60 min on two separate occasions 1 h after ingesting 1) 5 mg·kg-1 caffeine (CAF) or 2) 5 mg·kg-1 placebo (PLA), in a double-blinded, randomized, and counterbalanced order. Environmental conditions were 30.6 ± 0.9°C, 31 ± 1% relative humidity (RH). The end-exercise rise in esophageal temperature (ΔTes) from baseline was greater with CAF in the HAB group (CAF = 0.88 ± 0.29°C, PLA = 0.62 ± 0.34°C, P < 0.001), but not in the NHAB group (CAF = 1.00 ± 0.42°C, PLA = 1.00 ± 0.39°C, P = 0.94). For a given change in mean body temperature, rises in % of maximum skin blood flow were attenuated with CAF on the forearm (P = 0.015) and back (P = 0.021) in the HAB group, but not in the NHAB group (P ≥ 0.65). Dry heat loss was similar in the HAB (CAF = 31 ± 5 W·m-2, PLA = 33 ± 7 W·m-2) and NHAB groups (CAF = 31 ± 3 W·m-2, PLA 30 ± 4 W·m-2) (P ≥ 0.37). There were no differences in whole body sweat losses in both groups (HAB: CAF = 0.59 ± 0.15 kg, PLA = 0.56 ± 0.17 kg, NHAB:CAF = 0.53 ± 0.19 kg, PLA 0.52 ± 0.19 kg) (P ≥ 0.32). As the potential for both dry and evaporative heat loss was uninhibited by caffeine, we suggest that the observed ΔTes differences with CAF in the HAB group were due to alterations in internal heat distribution. Our findings support the common practice of participants abstaining from caffeine before participation in thermoregulatory research studies in compensable conditions. NEW & NOTEWORTHY We provide empirical evidence that acute caffeine ingestion exerts a thermoregulatory effect during exercise in the heat in caffeine-habituated individuals but not in nonhabituated individuals. Specifically, caffeine habituation was associated with a greater rise in esophageal temperature with caffeine compared with placebo, which appears to be driven by a blunted skin blood flow response. In contrast, no thermoregulatory differences were observed with caffeine in nonhabituated individuals. Caffeine did not affect sweating responses during exercise in the heat. [ABSTRACT FROM AUTHOR]

The endothelin-B (ETB) receptor is a key regulator of vascular endothelial function in women. We have previously shown that the ETB receptor mediates vasodilation in young women, an effect that is lost after menopause. However, the direct impact of changes in estradiol (E2) on ETB receptor function in women remains unclear. Therefore, the purpose of this study was to test the hypothesis that E2 exposure modulates ETB receptor-mediated dilation in young women. Fifteen young women (24 ± 4 yr, 24 ± 3 kg/m²) completed the study. Endogenous sex hormone production was suppressed with daily administration of a gonadotropin- releasing hormone antagonist (GnRHant; Ganirelix) for 10 days; E2 (0.1 mg/day, Vivelle-Dot patch) was added back on days 4-10. We measured vasodilation in the cutaneous microcirculation (microvascular endothelial function) via local heating (42°C) on day 4 (GnRHant) and day 10 (GnRHant þ E2) using laser Doppler flowmetry coupled with intradermal microdialysis during perfusions of lactated Ringer's (control) and ETB receptor antagonist (BQ-788, 300 nM). During GnRHant, vasodilatory responses to local heating were enhanced with ETB receptor blockade (control: 83 ± 9 vs. BQ-788: 90 ±5%CVCmax, P = 0.004). E2 administration improved vasodilation in the control site (GnRHant: 83 ± 9 vs. GnRHant þ E2: 89 ± 8%CVCmax, P = 0.036). Furthermore, cutaneous vasodilatory responses during ETB receptor blockade were blunted after E2, administration (control: 89 ± 8 vs. BQ-788: 84 ± 8%CVCmax, P = 0.047). These data demonstrate that ovarian hormones, specifically E2, modulate ETB receptor function and contribute to the regulation of microvascular endothelial function in young women. [ABSTRACT FROM AUTHOR]

We tested the hypotheses that 1) cutaneous microvascular function is impaired by acute normobaric and chronic hypobaric hypoxia and 2) that the superoxide free radical (via NADPH oxidase or xanthine oxidase) contributes to this impairment via nitric oxide (NO) scavenging. Local heating-induced cutaneous hyperemia (39 °C) was measured in the forearm of 11 male lowlanders at sea level (SL) and following 14–18 days at high altitude (HA; 4340 m in Cerro de Pasco, Peru), and compared to 11 highlanders residing permanently at this elevation. Cutaneous vascular conductance (CVC; laser-Doppler flux/mean arterial pressure) was not different during 39 °C [control site: 73 (19) vs. 71 (18)%max; P = 0.68] between normoxia and acute normobaric hypoxia (F I O 2 = 0.125; equivalent to HA), respectively. At HA, CVC was reduced during 39 °C in lowlanders compared to SL [control site: 54 (14) vs. 73 (19)%max; P < 0.01] and was lower in Andean highlanders compared to lowlanders at HA [control site: 50 (24) vs. 54 (14)%max; P = 0.02]. The NO contribution to vasodilation during 39 °C (i.e., effect of NO synthase inhibition) was reduced in lowlanders at HA compared to SL [control site: 41 (11) vs 49 (10)%max; P = 0.04] and in Andean highlanders compared to lowlanders at HA [control site: 32 (21) vs. 41 (11)%max; P = 0.01]. Intradermal administration (cutaneous microdialysis) of the superoxide mimetic Tempol, inhibition of xanthine oxidase (via allopurinol), or NADPH oxidase (via apocynin) had no influence on cutaneous endothelium-dependent dilation during any of the conditions (all main effects of drug P > 0.05). These results suggest that time at HA impairs NO-mediated cutaneous vasodilation independent of enzymatic superoxide formation. [Display omitted] • Oxidative stress has been associated with vascular dysfunction at high altitude. • Intradermal microdialysis in the skin circulation inhibits certain pathways of superoxide production and scavenges superoxide free radicals. • Lower skin blood flow responses to local heating occurred at high altitude in lowlanders and compared to Andean highlanders, but not in acute normobaric hypoxia compared to normoxia. • Superoxide suppression did not mitigate vascular dysfunction but it was observed that nitric oxide-mediated vasodilation was impaired at high altitude. [ABSTRACT FROM AUTHOR]

Human thermoregulatory control is often evaluated through the relationship between thermoeffector output and core or mean body temperature. In addition to providing a general indication of whether a variable of interest alters thermoregulatory control, this relationship is often used to determine how this alteration may occur. This latter interpretation relies upon two parameters of the thermoeffector output-body temperature relationship: the onset threshold and thermosensitivity. Traditionally, changes in the onset threshold and thermosensitivity are interpreted as "central" or "peripheral" modulation of thermoregulatory control, respectively. This mini-review revisits the origins of the thermoeffector output-body temperature relationship and its use to interpret "central" or "peripheral" modulation of thermoregulatory control. Against this background, we discuss the strengths and weaknesses of this approach and highlight that "central" thermoregulatory control reflects the neural control of body temperature whereas "peripheral" thermoregulatory control reflects properties specific to the thermoeffector organs. We highlight studies that employed more direct approaches to investigate the neural control of body temperature and peripheral properties of thermoeffector organs. We conclude by encouraging future investigations interested in studying thermoregulatory control to more directly investigate the component of the thermoeffector loop under investigation. [ABSTRACT FROM AUTHOR]

New Findings: What is the central question of this study?Are regional differences in nitric oxide (NO)‐dependent cutaneous vasodilatation during local skin heating present in young adults?What is the main finding and its importance?NO‐dependent cutaneous vasodilatation varied across the body. The abdomen demonstrated larger NO contributions, while the chest demonstrated smaller NO contributions, compared to other regions. This exploratory work is an important first step in characterizing regional heterogeneity of cutaneous microvascular control across the torso and limbs. Equally, it serves to generate hypotheses for future studies examining regional cutaneous microvascular control in ageing and disease. Regional variations in cutaneous vasodilatation during local skin heating exist across the body. While nitric oxide (NO) is a well‐known modulator of this response, the extent of regional differences in NO‐dependent cutaneous vasodilatation during local skin heating remains uncertain. In 16 habitually active young adults (8 females; 25 ± 5 years), cutaneous vascular conductance, normalized to maximum vasodilatation (% CVCmax), was assessed at the upper chest, abdomen, dorsal forearm, thigh and lateral calf during local skin heating. Across all regions, local skin temperatures were simultaneously increased from 33 to 42°C (1°C per 10 s), and held until a stable heating plateau was achieved (∼40 min). Next, with local skin temperature maintained at 42°C, 20 mM of NG‐nitro‐l‐arginine methyl ester (l‐NAME) was continuously infused at each site until a stable l‐NAME plateau was achieved (∼40 min). The difference between heating and l‐NAME plateaus was identified as the NO contribution for each region. There was no evidence for region‐specific responses at baseline (P = 0.561), the heating plateau (P = 0.351) or l‐NAME plateau (P = 0.082), but there was for the NO contribution (P = 0.048). Overall, point estimates for between‐region differences in the NO contribution varied across the body from 0 to 19% CVCmax. The greatest effects were observed for the abdomen, wherein the NO contribution was consistently greater than for the other regions (range: 9–19% CVCmax). The chest was consistently lower than the other regions (range: 7–19% CVCmax). The smallest effects were observed between limb regions (range: 0–2% CVCmax). These findings advance our understanding of the mechanisms influencing regional variations in the cutaneous vasodilator response to local skin heating in young adults. [ABSTRACT FROM AUTHOR]