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Measurement of blood flow during exercise is crucial for understanding physiological responses and performance outcomes. However, traditional methods are often invasive, costly, or require substantial training, limiting widespread research in this area. This study introduces the innovative use of limb-affixed ultrasound probe holders for vascular imaging during exercise to overcome these challenges. We investigated a commercially available probe holder, the Usono ProbeFix dynamic (PFD), in capturing artery diameter and blood velocity during dynamic exercise compared with a trained sonographer. Twenty healthy adults (11 females) underwent simultaneous imaging of the brachial artery and superficial femoral artery (SFA) using both manual and PFD imaging on separate days. Data were collected for 60 s at rest on a cycle ergometer and after 4 min of cycling at 50, 100, and 150 W. The PFD was comparable with a trained sonographer at rest (both 99 ± 2%) but demonstrated superiority in capturing blood velocity in the inactive limb (main effect of scanning condition P < 0.01; e.g., 150 W exercise: 85 ± 21% vs. 74 ± 25%). There was no effect of scanning condition on velocity capture success in the SFA (main effect: 69 ± 21% vs. 65 ± 16%; P = 0.42). A systematic constriction of brachial artery diameter (∼0.02 cm) was noted in the PFD condition (P < 0.01), likely due to the compression of the shallow artery. The findings suggest that ultrasound probe holders offer a promising solution for increasing accessibility to exercising blood flow in vascular physiology research, though require considerations for data cleaning and diameter assessment. Further investigation is warranted to optimize the application of these devices in dynamic exercise scenarios. NEW & NOTEWORTHY: This study explores an ultrasound probe holder (PFD) for measuring blood flow during exercise, addressing the limitations of traditional methods. We compared PFD imaging with manual scanning in capturing artery diameter and blood velocity during cycling exercise. Results showed that the PFD matched trained sonographer accuracy at rest and outperformed them in capturing blood velocity during exercise in the inactive limb but not active limb. We highlight the PFD's potential impact in vascular physiology research. [ABSTRACT FROM AUTHOR]

The accuracy of femoral artery blood flow measurements via Doppler ultrasound hinges on assumptions of laminar flow upstream of the femoral bifurcation. Existing scanning guidelines recommend a minimum proximity to the flow divider of 2–3 cm for avoiding multidirectional blood flow yet lack experimental evidence to support this recommendation. This study aimed to determine the minimum distance required to avoid multidirectional flow contamination near the femoral bifurcation and to assess the reliability of vector flow imaging (VFI) in these measurements. Twenty healthy adults (10 females, 25 ± 4 yr) participated in this study. Ultrasound VFI was used to visualize blood flow patterns and quantify flow uniformity via vector concentration coefficient (VCC), and multidirectional flow length was quantified at rest in triplicate (n = 20), postisometric contraction (n = 20), and during thigh cuffing (n = 10). At rest, the mean multidirectional flow length was 3.12 ± 0.59 cm, which decreased to 2.80 ± 0.66 cm postcontraction (P = 0.02). Thigh cuffing (80 mmHg) resulted in a multidirectional flow length of 2.75 ± 0.64 cm, not significantly different from rest (P = 0.69). Males exhibited a shorter multidirectional flow length compared with females (mean difference: 0.31 ± 0.71 cm, P = 0.05). The VCC increased from 0.39 ± 0.08 at rest to 0.57 ± 0.15 postcontraction (P < 0.01), indicating increased flow uniformity. Reliability metrics demonstrated good-to-excellent reproducibility at rest, with intraclass correlation coefficient [ICC(3,1)] = 0.85 and 0.84 and coefficient of variation (CV)% = 7.1 ± 6.2% and 7.5 ± 4.5% for multidirectional flow length and VCC, respectively. Our data suggest a minimum scanning proximity of 3.5 cm to the femoral bifurcation to ensure that blood flow assessments are free of multidirectional flow and invite further study in different body positions and arteries of interest to increase rigor in this area. NEW & NOTEWORTHY: Current ultrasound scanning guidelines to avoid multidirectional flow contamination in the femoral artery of 2–3 cm lack supporting evidence. We used vector flow imaging to report the multidirectional flow length during rest and manipulation of downstream vessel resistance in males and females. We suggest measurements at least 3.5 cm upstream from the femoral bifurcation to minimize multidirectional flows. This study also supports reliability of vector flow imaging for femoral artery assessments, with good-to-excellent reproducibility of results. [ABSTRACT FROM AUTHOR]

We recently explored the cardiopulmonary interactions during partial unloading of the respiratory muscles during exercise. Expanding upon this work, we present a noteworthy case study whereby we eliminated the influence of respiration on cardiac function in a conscious but mechanically ventilated human during exercise. This human was a young healthy endurance-trained male who was mechanically ventilated during semi-recumbent cycle exercise at 75 Watts (W) (∼30% Wmax). During mechanically ventilated exercise, esophageal pressure was reduced to levels indistinguishable from the cardiac artefact which led to a 94% reduction in the power of breathing. The reduction in respiratory pressures and respiratory muscle work led to a decrease in cardiac output (−6%), which was due to a reduction in stroke volume (−13%), left ventricular end-diastolic volume (−15%), and left-ventricular end-systolic volume (−17%) that was not compensated for by heart rate. Our case highlights the influence of extreme mechanical ventilation on cardiac function while noting the possible presence of a maximal physiological limit to which respiration (and its associated pressures) impacts cardiac function when the power of breathing is maximally reduced. [ABSTRACT FROM AUTHOR]

Blood volume shifts during postural adjustment lead to irregular distension of the internal jugular vein (IJV). In microgravity, distension may contribute to flow stasis and thromboembolism, though the regional implications and associated risk remain unexplored. We characterized regional differences in IJV volume distension and flow complexity during progressive head-down tilt (HDT) (0°, −6°, −15°, −30°) using conventional ultrasound and vector flow imaging. We also evaluated low-pressure thigh cuffs (40 mmHg) as a fluid shifting countermeasure during −6° HDT. Total IJV volume expanded 139 ± 95% from supine position (4.6 ± 2.7 mL) to −30° HDT (10.3 ± 5.0 mL). Blood flow profiles had greater vector uniformity at the cranial IJV region (P < 0.01) and became more dispersed with increasing tilt (P < 0.01). Qualitatively, flow was more uniform throughout the IJV during its early flow cycle phase and more disorganized during late flow phase. This disorganized flow was accentuated closer to the vessel wall, near the caudal region, and during greater HDT. Low-pressure thigh cuffs during −6° HDT decreased IJV volume at the cranial region (−12 ± 15%; P < 0.01) but not the caudal region (P = 0.20), although flow uniformity was unchanged (both regions, P > 0.25). We describe a distensible IJV accommodating large volume shifts along its length. Prominent flow dispersion was primarily found at the caudal region, suggesting multidirectional blood flow. Thigh cuffs appear effective for decreasing IJV volume but effects on flow complexity are minor. Flow complexity along the vessel length is likely related to IJV distension during chronic volume shifting and may be a precipitating factor for flow stasis and future thromboembolism risk. NEW & NOTEWORTHY: The internal jugular vein (IJV) facilitates cerebral outflow and is sensitive to volume shifts. Concerns about IJV expansion and fluid flow behavior in astronauts have surfaced following thromboembolism reports. Our study explored regional volume distension and blood flow complexity in the IJV during progressive volume shifting. We observed stepwise volume distension and increasing flow dispersion with head-down tilting across all regions. Flow dispersion may pose a risk of future thromboembolism during prolonged volume shifts. [ABSTRACT FROM AUTHOR]

Carotid artery longitudinal wall motion (CALM) is a novel preclinical marker for atherosclerosis that describes the axial anterograde and retrograde motion of the intima–media complex. While regular physical activity and sex are known to independently influence arterial stiffness, their roles on axial arterial wall behaviour are unknown. The purpose of this study is to examine whether physical activity and sex impact CALM. We hypothesized that CALM retrograde displacement and total amplitude would be greater in females and active individuals, as a function of arterial stiffness. Fifty-seven young healthy adults (30 females; aged 22 ± 3 years) were evaluated for CALM outcomes and arterial stiffness and grouped by physical activity based on active (V̇O2 = 44.2 ± 8.9 mL/kg/min) or sedentary (V̇O2 = 33.7 ± 6.7 mL/kg/min) lifestyles defined by the Canadian 24-Hour Movement Guidelines. Arterial stiffness and CALM were measured by carotid–femoral pulse wave velocity (cfPWV) and vascular ultrasound at the right common carotid artery with speckle tracking analysis, respectively. cfPWV was greater in males (p < 0.01) with no interaction between sex and physical activity (p = 0.90). CALM anterograde displacement was greater in males (p = 0.03) resulting in a forward shift in total CALM pattern, which became less prominent when controlling for mean arterial pressure (p = 0.06). All other CALM outcomes were not different between activity and sex. V̇O2max was not correlated to any CALM outcome (all p > 0.05). Apparent sex differences in vascular function extend to novel CALM outcomes but may be confounded by blood pressure. We recommend sex-balanced design and reporting in future studies due to possible anterograde-shifted CALM patterns in healthy males. [ABSTRACT FROM AUTHOR]