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Purpose: To investigate the effects of repeated-sprint training with voluntary hypoventilation at low (RSH-VHL) and high (RS-VHH) lung volume on repeated-sprint ability (RSA) in female athletes. Methods: Over a 6-week period, 24 female soccer players completed 12 sessions of repeated 30-m running sprints with end-expiratory breath holding (RSH-VHL, n = 8), end-inspiratory breath holding (RS-VHH, n = 8), or unrestricted breathing (RS-URB, n = 8). Before and after training, a running RSA test consisting of performing 30-m all-out sprints until exhaustion was implemented. Results: From before to after training, the number of sprints completed during the RSA test was increased in both RSH-VHL (19.3 [0.9] vs 22.6 [0.9]; P <.01) and RS-VHH (19.3 [1.5] vs 20.5 [1.7]; P <.01) but not in RS-URB (19.4 [1.3] vs 19.5 [1.7]; P =.67). The mean velocity and the percentage decrement score calculated over sprints 1 to 17 were, respectively, higher (82.2% [1.8%] vs 84.6% [2.1%] of maximal velocity) and lower (23.7% [3.1%] vs 19.4% [3.2%]) in RSH-VHL (P <.01), whereas they remained unchanged in RS-VHH and RS-URB. The mean arterial oxygen saturation recorded during training at the end of the sprints was lower in RSH-VHL (92.1% [0.4%]) than in RS-VHH (97.3% [0.1%]) and RS-URB (97.8% [0.1%]). Conclusions: This study shows that female athletes can benefit from the RSH-VHL intervention to improve RSA. The performance gains may have been limited by the short sprinting distance with end-expiratory breath holding, which provoked only moderate hypoxemia. The increase in the number of sprints in RS-VHH seems to show that factors other than hypoxia may have played a role in RSA improvement. [ABSTRACT FROM AUTHOR]

Background: This study aimed to investigate the associations between dyscapnia, ventilatory variables, and mortality. We hypothesized that the association between mechanical power or ventilatory ratio and survival is mediated by dyscapnia. Methods: Patients with moderate or severe acute respiratory distress syndrome (ARDS), who received mechanical ventilation within the first 48 h after admission to the intensive care unit for at least 48 h, were included in this retrospective single-center study. Values of arterial carbon dioxide (PaCO2) were categorized into "hypercapnia" (PaCO2 ≥ 50 mm Hg), "normocapnia" (PaCO2 36-49 mmHg), and "hypocapnia" (PaCO2 ≤ 35 mm Hg). We used path analyses to assess the associations between ventilatory variables (mechanical power and ventilatory ratio) and mortality, where hypocapnia or hypercapnia were included as mediating variables. Results: Between December 2017 and April 2021, 435 patients were included. While there was a significant association between mechanical power and hypercapnia (BEM = 0.24 [95% CI: 0.15; 0.34], P <.01), there was no significant association between mechanical power or hypercapnia and ICU mortality. The association between mechanical power and intensive care unit (ICU) mortality was fully mediated by hypocapnia (BEM = −0.10 [95% CI: −0.19; 0.00], P =.05; BMO = 0.38 [95% CI: 0.13; 0.63], P <.01). Ventilatory ratio was significantly associated with hypercapnia (B = 0.23 [95% CI: 0.14; 0.32], P <.01). There was no significant association between ventilatory ratio, hypercapnia, and mortality. There was a significant effect of ventilatory ratio on mortality, which was fully mediated by hypocapnia (BEM = −0.14 [95% CI: −0.24; −0.05], P <.01; BMO = 0.37 [95% CI: 0.12; 0.62], P <.01). Conclusion: In mechanically ventilated patients with moderate or severe ARDS, the association between mechanical power and mortality was fully mediated by hypocapnia. Likewise, there was a mediating effect of hypocapnia on the association between ventilatory ratio and ICU mortality. Our results indicate that the debate on dyscapnia and outcome after ARDS should consider the impact of ventilatory variables. [ABSTRACT FROM AUTHOR]

Aging invariably decreases sensory and motor stimuli and affects several neuronal systems and their connectivity to key brain regions, including those involved in breathing. Nevertheless, further investigation is needed to fully comprehend the link between senescence and respiratory function. Here, we investigate whether a mouse model of accelerated senescence could develop central and peripheral respiratory abnormalities. Adult male Senescence Accelerated Mouse Prone 8 (SAMP8) and the control SAMR1 mice (10 months old) were used. Ventilatory parameters were assessed by whole-body plethysmography, and measurements of respiratory input impedance were performed. SAMP8 mice exhibited a reduction in the density of neurokinin-1 receptor immunoreactivity in the entire ventral respiratory column. Physiological experiments showed that SAMP8 mice exhibited a decreased tachypneic response to hypoxia (FiO2 = 0.08; 10 min) or hypercapnia (FiCO2 = 0.07; 10 min). Additionally, the ventilatory response to hypercapnia increased further due to higher tidal volume. Measurements of respiratory mechanics in SAMP8 mice showed decreased static compliance (Cstat), inspiratory capacity (IC), resistance (Rn), and elastance (H) at different ages (3, 6, and 10 months old). SAMP8 mice also have a decrease in contractile response to methacholine compared to SAMR1. In conclusion, our findings indicate that SAMP8 mice display a loss of the NK1-expressing neurons in the respiratory brainstem centers, along with impairments in both central and peripheral respiratory mechanisms. These observations suggest a potential impact on breathing in a senescence animal model. [ABSTRACT FROM AUTHOR]

An overactive orexin (OX) system is associated with neurogenic hypertension and an exaggerated chemoreflex in spontaneously hypertensive rats (SHRs). However, the chronology and mechanism of this association is unclear. We hypothesized that increased postnatal neurogenesis of OX neurons in SHRs precedes and contributes to the aberrant increase in mean arterial blood pressure (MAP) and the exaggerated response to hypercapnia during postnatal development. Using immunohistochemical methods and bromodeoxyuridine, we mapped the timeline of orexin neuron neurogenesis and maturation during early postnatal development. We then used whole-body plethysmography with EEG and EMG to map the development of mean arterial pressure (MAP) and state regulation. Finally, we used OX-targeted saporin toxin to determine the effects of eliminating excess OX neurons on the elevated MAP and exaggerated chemoreflex in adult SHRs. We found that both SHRs and Wistar-Kyoto (WKY) rats experienced postnatal increases in OX neurons. However, SHRs experienced a greater increase than WKY rats before P15, which led to significantly more OX neurons in SHRs than age-matched WKY controls by P15-16 (3,720 ± 780 vs. 2,406 ± 363, p = 0.005). We found that neurogenesis, as evidenced by BrdU staining in OX-positive neurons, was the primary contributor to the excess OX neurons in SHRs during early postnatal development. While SHRs develop more OX neurons by P15-16, SHRs and normotensive WKY control rats have similar MAP during postnatal development until P25 in wakefulness (81.6 ± 6.6 vs. 67.5 ± 6.8 mmHg, p = 0.006) and sleep (79.3 ± 6.1 vs. 66.6 ± 6.5, p = 0.009), about 10 days after the surge of OX neurons. By selectively eliminating excess (~30%) OX neurons in SHRs, we saw a significantly lowered MAP and hypercapnic ventilatory chemoreflex compared to non-lesioned SHRs at P40. Additionally, we found unique signatures in state indicative of the attention defecit phenotype commonly associated with this model. We suggest that the postnatal increase of OX neurons, primarily attributed to exaggerated postnatal OX neurogenesis, may be necessary for the development of higher MAP and exaggerated chemoreflex in SHRs, and modulation of the overactive OX system may have a potential therapeutic effect during the pre-hypertensive period. [ABSTRACT FROM AUTHOR]

Background: Prolonged electroencephalographic depression during surgery is associated with poor outcomes for patients. However, the published literature on electroencephalographic depression caused by a sudden increase in the partial pressure of end-tidal carbon dioxide (PETCO2) is lacking. Case presentation: We report four patients who were scheduled for laparoscopic liver surgery under general anesthesia. During the process of EEG monitoring with Sedline, four patients experienced electroencephalographic depression closely after a sudden increase in PETCO2. The four patients showed that electroencephalographic depression mainly manifested as a slow in EEG frequency, a reduction in the amplitude and power of EEG, and a decrease in spectral edge frequency. Patient state index was elevated in three cases. Conclusions: To summarize, our patients showed EEG depression when PETCO2 suddenly increased, which suggests that clinical doctors should be alert to electroencephalographic depression when the PETCO2 abruptly increases. EEG monitoring devices should be applied in patients with possible hypercapnia. Anesthesiologists must comprehensively interpret the raw EEG, spectral edge frequency, and density spectral array data, in addition to patient sedation index values. [ABSTRACT FROM AUTHOR]

Purpose: To investigate the effects of a repeated-sprint training in hypoxia induced by voluntary hypoventilation at low lung volume (RSH-VHL) including end-expiratory breath holding (EEBH) of maximal duration. Methods: Over a 4-week period, twenty elite judo athletes (10 women and 10 men) were randomly split into two groups to perform 8 sessions of rowing repeated-sprint exercise either with RSH-VHL (each sprint with maximal EEBH) or with unrestricted breathing (RSN, 10-s sprints). Before (Pre-), 5 days after (Post-1) and 12 days after (Post-2) the last training session, participants completed a repeated-sprint ability (RSA) test on a rowing ergometer (8 × 25-s "all-out" repetitions interspersed with 25 s of passive recovery). Power output (PO), oxygen uptake, perceptual-motor capacity (turning off a traffic light with a predetermined code), cerebral (Δ[Hbdiff]) and muscle (Δ[Hb/Mb]diff) oxygenation, cerebral total haemoglobin concentration (Δ[THb]) and muscle total haemoglobin/myoglobin concentration (Δ[THb/Mb]) were measured during each RSA repetition and/or recovery period. Results: From Pre-to Post-1 and Post-2, maximal PO, mean PO (MPO) of the first half of the test (repetitions 1-4), oxygen uptake, end-repetition cerebral Δ[Hbdiff] and Δ[THb], end-repetition muscle Δ[Hb/Mb]diff and Δ[THb/Mb] and perceptualmotor capacity remained unchanged in both groups. Conversely, MPO of the second half of the test (repetitions 5-8) was higher at Post-1 than at Pre-in RSHVHL only (p < 0.01), resulting in a lower percentage decrement score over the entire RSA test (20.4% ± 6.5% vs. 23.9% ± 7.0%, p = 0.01). Furthermore, MPO (5-8) was greater in RSH-VHL than in RSN at Post-1 (p = 0.04). These performance results were accompanied by an increase in muscle Δ[THb/Mb] (p < 0.01) and a concomitant decrease in cerebral Δ[THb] (p < 0.01) during the recovery periods of the RSA test at Post-1 in RSH-VHL. Conclusion: Four weeks of RSH-VHL including maximal EEBH improved the ability of elite judo athletes to repeat high-intensity efforts. The performance improvement, observed 5 days but not 12 days after training, may be due to enhanced muscle perfusion. The unchanged oxygen uptake and the decrease in cerebral regional blood volume observed at the same time suggest that a blood volume redistribution occurred after the RSH-VHL intervention to meet the increase in muscle perfusion. [ABSTRACT FROM AUTHOR]

Introduction: Asthma is a chronic inflammatory condition affecting the airways, characterized by an exaggerated response of the trachea-bronchial system to various stimuli. This condition leads to significant narrowing of the airways, which can be alleviated through medication or may resolve spontaneously Therefore, this study focuses on arterial blood gas analysis in patients experiencing acute severe asthma and chronic bronchial asthma upon hospital admission, with particular attention to acid-base status, PaO2, PaCO2, and HCO3- levels. Aim and Objectives: To compare arterial blood gas analysis of acute severe bronchial asthma with chronic bronchial asthma. Materials and Methods: A cross-sectional study was conducted involving 50 asthmatic patients aged between 20 and 75 years, who presented at a tertiary care hospital over a 12-month period. The study excluded pregnant women, children, smokers, and individuals with other respiratory conditions. The entire procedure was thoroughly explained to each patient, and informed consent was obtained. Results: P-value for comparison pf Ph in between the groups was <0.05 which was statistically significant in between the groups. P-value for comparison of mean PaCO2 levels in between the groups was <0.05 which is statistically significant in between the groups. P-value for comparison if PaO2levels in between the groups was > 0.05 which was statistically insignificant in between the groups. Conclusion: It is important to note that arterial blood gas analysis alone does not adequately reflect the severity of an asthma attack; it should be supplemented with further assessments, including Peak Expiratory Flow Rate (PEFR) and Forced Expiratory Volume in one second (FEV1), in conjunction with a clinical evaluation of signs and symptoms. [ABSTRACT FROM AUTHOR]

Coastal marine environments are characterized by daily, seasonal and long-term changes in both O2 and CO2, driven by local biotic and abiotic factors. The neuroepithelial cells (NECs) of fish are thought to be the putative chemoreceptors for sensing oxygen and CO2, and, thus, NECs play a key role in detecting these environmental changes. However, the role of NECs as chemosensors in marine fish remains largely understudied. In this study, the NECs of marine threespine sticklebacks (Gasterosteus aculeatus) were characterized using immunohistochemistry. We then determined if there were changes in NEC size and density, and in gill morphology in response to either mild (10 kPa) or moderate (6.8 kPa) hypoxia and two levels of elevated CO2 (1,500 and 3,000 µatm). We found that the NECs of stickleback contained synaptic vesicles and were innervated, and were 50–300% larger and 2 to 4 times more abundant than in other similar sized freshwater fishes. NEC size and density were largely unaffected by exposure to hypoxia, but there was a 50% decrease in interlamellar cell mass (ILCM) in response to mild and moderate hypoxia. NECs increased in size, but not abundance in response to elevated CO2. Moreover, fish exposed to moderate or elevated CO2 had 53–78% larger ILCMs compared to control fish. Our results demonstrated that adult marine sticklebacks have NECs that can respond to environmentally relevant pCO2 and likely hypoxia, which highlights the importance of NECs in marine fishes under the heterogeneity of environmental conditions in coastal areas. [ABSTRACT FROM AUTHOR]

The changes in brain function in response to mild head injury are usually subtle and go undetected. Physiological biomarkers would aid in the early diagnosis of mild head injury. In this study we used hypercapnia to follow changes in cerebral vascular reactivity after repetitive mild head injury. We hypothesized head injury would reduce vascular reactivity. Rats were maintained on a reverse light-dark cycle and head impacted daily at 24 h intervals over three days. All head impacts were delivered while rats were fully awake under red light illumination. There was no neuroradiological evidence of brain damage. After the 3rd impact rats were exposed to 5% CO2 and imaged for changes in BOLD signal. All imaging was done while rats were awake without the confound of anesthesia. The data were registered to a 3D MRI rat atlas with 171 segmented brain areas providing site specific information on vascular reactivity. The changes in vascular reactivity were not uniform across the brain. The prefrontal cortex, somatosensory cortex and basal ganglia showed the hypothesized decrease in vascular reactivity while the cerebellum, thalamus, brainstem, and olfactory system showed an increase in BOLD signal to hypercapnia. [ABSTRACT FROM AUTHOR]

Respiratory failure is a common problem particularly in patients with pre-existing respiratory disease but also in previously well patients in the perioperative setting. It carries a 90-day mortality of above 40% representing a high-risk patient population. This article discusses the causes, presentation, assessment, and management of respiratory failure, along with a brief overview of perioperative risk prediction and pathophysiology. [ABSTRACT FROM AUTHOR]

Competitive freediving is associated with extreme physiologic challenges due to the effects of apnea, submersion in water, and increased ambient pressure. There has nevertheless been a continued progression of world records across freediving disciplines in recent years, with breath-hold times exceeding 10 minutes, and reaching diving depths beyond 200 meters of seawater. The main physiological determinants of breath-hold endurance are the available oxygen stores, i.e., intrapulmonary gas volume, inspired gas concentration, and rate of oxygen consumption. Other factors such as psychological and inherent factors contribute to the individual tolerance to an increasing respiratory stimulus with prolonged breath-hold duration. › A freediving athlete must be able to tolerate apnea to stay underwater long enough to reach great distance or depth and resurface safely. Elite freedivers exhibit somewhat remarkable physiological adaptations such as a more pronounced diving-response and hypercapnia tolerance compared to non-divers, as well as metabolic and cerebrovascular adaptations. To reach great depths, elite freedivers employ a breathing technique called glossophyryngeal insufflation (GI) that is enlarging the ratio of total lung capacity to residual volume, thus, mitigating risk of lung squeeze and increasing intrapulmonary gas volume, and thereby enhancing available oxygen stores. Pulmonary anatomy and physiology could not be accounted to restrict the breath-hold diving depths achieved by competitive athletes. › However, the acutely increased intrapulmonary pressure during GI is transmitted to the pulmonary vasculature, thereby eliciting a right ventricular pressure overload, and left ventricular dysfunction that may augment hypotension and syncope during glossopharyngeal insufflation. Due to extreme diffusion gradients between alveolar pN2 and N2 pressures in the body tissues at great depth, N2 will be forced into blood and body tissues during descent, elevating risk of N2 narcosis and decompression illness during deep dives. Breath-hold training and preparation have been shown to enhance breath-hold performance. › This review highlights recent data on the profound cardiovascular, respiratory, and gas exchange effects that are observed in competitive freedivers, and discusses possible adaptations and risks for humans. [ABSTRACT FROM AUTHOR]

Many biological mechanisms of aging well converge with radiation's biological effects. We used scientific insights from the field of aging to establish a novel hypoxic-hypercapnic environment (HHE) concept for radioprotection. According to this concept, HHE which possesses an anti-aging and longevity-promoting potential, should also act as a radiomitigator and radioprotector. As such, it might contribute greatly to the safety and wellbeing of individuals exposed to high levels of radiation, whether in planned events (e.g. astronauts) or in unplanned events (e.g. first responders in nuclear accidents). [ABSTRACT FROM AUTHOR]

The locus coeruleus (LC), nucleus tractus solitarius (NTS), and retrotrapezoid nucleus (RTN) are critical chemosensory regions in the brainstem. In the LC, acid-sensing ion channels and proton pumps serve as H+ sensors and facilitate the transition from non-rapid eye movement (NREM) to rapid eye movement (REM) sleep. Interestingly, the potassium inward rectifier (KIR) channels in the LC, NTS, and RTN also act as H+-sensors and are a primary target for improving sleep in obstructive sleep apnea and Rett syndrome patients. However, the role of Kir channels in NREM to REM sleep transition for H+ homeostasis is not known. Male Wistar rats were surgically prepared for chronic sleep–wake recording and drug delivery into the LC, NTS, and RTN. In different animal cohorts, microinjections of the Kir channel inhibitor, barium chloride (BaCl2), at concentrations of 1 mM (low dose) and 2 mM (high dose) in the LC and RTN significantly increased wakefulness and decreased NREM sleep. However, BaCl2 microinjection into the LC notably reduced REM sleep, whereas it didn’t change in the RTN-injected group. Interestingly, BaCl2 microinjections into the NTS significantly decreased wakefulness and increased the percent amount of NREM and REM sleep. Additionally, with the infusion of BaCl2 into the NTS, the mean REM sleep episode numbers significantly increased, but the length of the REM sleep episode didn’t change. These findings suggest that the Kir channels in the NTS, but not in the LC and RTN, modulate state transition from NREM to REM sleep. [ABSTRACT FROM AUTHOR]

Astronauts experience combined exposure to a cephalad fluid shift and mild hypercapnia during space missions, potentially contributing to health problems. Such combined exposure may weaken dynamic cerebral autoregulation. The magnitude of cephalad fluid shift varies between individuals, and dynamic cerebral autoregulation may be affected more by greater cephalad fluid shift during combined exposure. We evaluated the dose‐dependent effects of head‐down tilt (HDT) on dynamic cerebral autoregulation during acute combined exposure to HDT and 3% CO2 inhalation. Twenty healthy participants were randomly exposed to three angles of HDT (−5°HDT+CO2, −15°HDT+CO2 and −30°HDT+CO2). After 15 min of rest, participants inhaled room air for 10 min in a horizontal body position, then inhaled 3% CO2 for 10 min under HDT. The last 6 min of data were used for analysis in each stage. Arterial pressure waveforms were obtained using finger blood pressure, and blood velocity waveforms in the middle cerebral artery were obtained using transcranial Doppler ultrasonography. Dynamic cerebral autoregulation was evaluated by transfer function analysis between waveforms. Statistical analysis was performed by two‐way repeated‐measures analysis of variance. The index of transfer function gain in the low‐frequency range increased significantly with −15°HDT+CO2 and −30°HDT+CO2, but no changes were seen with −5°HDT+CO2. Phase in the low‐frequency range decreased significantly with all three protocols. These results of significant changes in indexes of both gain and phase during combined exposure to steep HDT (−15° to −30°) and 3% CO2 inhalation suggest weakened dynamic cerebral autoregulation with the combination of moderate cephalad fluid shift and mild hypercapnia. [ABSTRACT FROM AUTHOR]

Background: Identification of hypoxaemia and hypercapnia is essential for the diagnosis and treatment of acute respiratory failure. While arterial blood gas (ABG) analysis is standard for PO2 and PCO2 measurement, venous blood gas (VBG) analysis is increasingly used as an alternative. Previous systematic reviews established that VBG reporting of PO2 and PCO2 is less accurate, but the impacts on clinical management and patient outcomes are unknown. Aims: This study aimed to systematically review available evidence of the clinical impacts of using ABGs or VBGs and examine the arteriovenous difference in blood gas parameters. Methods: A comprehensive search of the MEDLINE, Embase and Cochrane Library databases since inception was conducted. Included studies were prospective or cross‐sectional studies comparing peripheral ABG to peripheral VBG in adult non‐critical care inpatients presenting with respiratory symptoms. Results: Of 15 119 articles screened, 15 were included. No studies were found that examined clinical impacts resulting from using VBG compared to ABG. Included studies focused on the agreement between ABG and VBG measurements of pH, PO2, PCO2 and HCO3−. Due to the heterogeneity of the included studies, qualitative evidence synthesis was performed. While the arteriovenous difference in pH and HCO3− was generally predictable, the difference in PO2 and PCO2 was more significant and less predictable. Conclusions: Our study reinforces the notion that VBG is not comparable to ABG for physiological measurements. However, a key revelation from our research is the significant lack of data regarding the clinical implications of using VBG instead of ABG, a common scenario in clinical practice. This highlights a critical knowledge gap. [ABSTRACT FROM AUTHOR]

The current standard treatment for obstructive sleep apnea (OSA), continuous positive airway pressure (CPAP), is characterized by a low adherence rate due to various factors including circuit-dependent carbon dioxide (CO 2) rebreathing, which can exacerbated by disparate factors, such as low PAP, use of auto-titrating PAP or ramps. However, risk factors for rebreathing are often overlooked or poorly understood in clinical practice. Therefore, our objective was to evaluate the extent of rebreathing occurring with commonly used CPAP masks across varying PAPs, tidal volumes, and respiratory rates. In a bench study, we assessed the rebreathing rate of nine masks interfacing a CPAP with a lung simulator providing different breathing respiratory rates (15 or 20 breaths/min) and tidal volumes (400, 500, 600, 700 and 750 mL). Additionally, a theoretical model was developed to describe the likelihood of CO 2 rebreathing from four different masks at various breathing settings. Overall, all masks performed worse in situations characterized by low PAPs, high tidal volumes, and high respiratory rates. However, Dreamwear, Nuance, Siesta, Vitera, and particularly V2 masks exhibited greater susceptibility to rebreathing compared to F20, P10, Brevida, and Rio masks for the same variations of PAPs or ventilatory parameters. The mathematical model suggested that the risk of rebreathing for Rio, P10 and Nuance mask is negligible for respiratory rates of 10 breaths/min or below. Circuit-dependent CO 2 rebreathing can be a common occurrence and warrants careful mask selection upon CPAP therapy initiation for optimal clinical outcomes. • Circuit rebreathing may subtly affect CPAP adherence, yet is poorly investigated. • Mask models exhibit varied CO 2 rebreathing risks depending on different factors. • Higher rebreathing rates are at low PAPs, high tidal volumes/breathing frequencies. • Rebreathing risk is low for specific masks, perhaps apt for CPAP naïve patients. • Mask with higher rebreathing rates might be indicated for mask noise complaints. [ABSTRACT FROM AUTHOR]

Background: Cerebrovascular reactivity (CVR) is a measure of the change in cerebral blood flow (CBF) in response to a vasoactive challenge. It is a useful indicator of the brain's vascular health. Purpose: To evaluate the factors that influence successful and unsuccessful CVR examinations using precise arterial and end‐tidal partial pressure of CO2 control during blood oxygen level–dependent (BOLD) MRI. Study Type: Retrospective. Subjects: Patients that underwent a CVR between October 2005 and May 2021 were studied (total of 1162 CVR examinations). The mean (±SD) age was 46.1 (±18.8) years, and 352 patients (43%) were female. Field Strength/Sequence: 3 T; T1‐weighted images, T2*‐weighed two‐dimensional gradient‐echo sequence with standard echo‐planar readout. Assessment: Measurements were obtained following precise hypercapnic stimuli using BOLD MRI as a surrogate of CBF. Successful CVR examinations were defined as those where: 1) patients were able to complete CVR testing, and 2) a clinically useful CVR map was generated. Unsuccessful examinations were defined as those where patients were not able to complete the CVR examination or the CVR maps were judged to be unreliable due to, for example, excessive head motion, and poor PETCO2 targeting. Statistical Analysis: Successful and unsuccessful CVR examinations between hypercapnic stimuli, and between different patterns of stimulus were compared with Chi‐Square tests. Interobserver variability was determined by using the intraclass correlation coefficient (P < 0.05 is significant). Results: In total 1115 CVR tests in 662 patients were included in the final analysis. The success rate of generating CVR maps was 90.8% (1012 of 1115). Among the different hypercapnic stimuli, those containing a step plus a ramp protocol was the most successful (95.18%). Among the unsuccessful examinations (9.23%), most were patient related (89.3%), the most common of which was difficulty breathing. Data Conclusion: CO2‐BOLD MRI CVR studies are well tolerated with a high success rate. Evidence Level: 4 Technical Efficacy: Stage 3 [ABSTRACT FROM AUTHOR]

Abstract Background Prolonged electroencephalographic depression during surgery is associated with poor outcomes for patients. However, the published literature on electroencephalographic depression caused by a sudden increase in the partial pressure of end-tidal carbon dioxide (PETCO2) is lacking. Case presentation We report four patients who were scheduled for laparoscopic liver surgery under general anesthesia. During the process of EEG monitoring with Sedline, four patients experienced electroencephalographic depression closely after a sudden increase in PETCO2. The four patients showed that electroencephalographic depression mainly manifested as a slow in EEG frequency, a reduction in the amplitude and power of EEG, and a decrease in spectral edge frequency. Patient state index was elevated in three cases. Conclusions To summarize, our patients showed EEG depression when PETCO2 suddenly increased, which suggests that clinical doctors should be alert to electroencephalographic depression when the PETCO2 abruptly increases. EEG monitoring devices should be applied in patients with possible hypercapnia. Anesthesiologists must comprehensively interpret the raw EEG, spectral edge frequency, and density spectral array data, in addition to patient sedation index values.

Abstract The locus coeruleus (LC), nucleus tractus solitarius (NTS), and retrotrapezoid nucleus (RTN) are critical chemosensory regions in the brainstem. In the LC, acid-sensing ion channels and proton pumps serve as H+ sensors and facilitate the transition from non-rapid eye movement (NREM) to rapid eye movement (REM) sleep. Interestingly, the potassium inward rectifier (KIR) channels in the LC, NTS, and RTN also act as H+-sensors and are a primary target for improving sleep in obstructive sleep apnea and Rett syndrome patients. However, the role of Kir channels in NREM to REM sleep transition for H+ homeostasis is not known. Male Wistar rats were surgically prepared for chronic sleep–wake recording and drug delivery into the LC, NTS, and RTN. In different animal cohorts, microinjections of the Kir channel inhibitor, barium chloride (BaCl2), at concentrations of 1 mM (low dose) and 2 mM (high dose) in the LC and RTN significantly increased wakefulness and decreased NREM sleep. However, BaCl2 microinjection into the LC notably reduced REM sleep, whereas it didn’t change in the RTN-injected group. Interestingly, BaCl2 microinjections into the NTS significantly decreased wakefulness and increased the percent amount of NREM and REM sleep. Additionally, with the infusion of BaCl2 into the NTS, the mean REM sleep episode numbers significantly increased, but the length of the REM sleep episode didn’t change. These findings suggest that the Kir channels in the NTS, but not in the LC and RTN, modulate state transition from NREM to REM sleep.

Common tenrecs (Tenrec ecaudatus) are fossorial mammals that use burrows during both active and hibernating seasons in Madagascar and its neighboring islands. Prevailing thought was that tenrecs hibernate for 8–9 months individually, but 13 tenrecs were removed from the same sealed burrow 1 m deep from the surface. Such group hibernation in sealed burrows presumably creates a hypoxic and/or hypercapnic environment and suggests that this placental mammal may have an increased tolerance to hypoxia and hypercapnia. Higher tolerances to hypoxia and hypercapnia have been documented for other mammals capable of hibernation and to determine if this is the case for tenrecs, we exposed them to acute hypoxia (4 h of 16 or 7% O2), progressive hypoxia (2 h of 16, 10 and 4% O2), or progressive hypercapnia (2 h of 2, 5 and 10% CO2) at cold (16 °C) or warm (28 °C) ambient temperatures (Ta). Oxygen equilibrium curves were also constructed on the whole blood of tenrecs at 10, 25, and 37 °C to determine if hemoglobin (Hb)-O2 affinity contributes to hypoxia tolerance. In animals held at 16 °C, normoxic and normocapnic levels of oxygen consumption rate ( V ˙ O 2 ), body temperature (Tb), and heart rate (HR) were highly variable between individuals. This inter-individual variation was greatly reduced in animals held at 28 °C for oxygen consumption rate and body temperature. Both hypoxia (acute and progressive) and progressive hypercapnia led to decreases in V ˙ O 2 as well as the variation in V ˙ O 2 between animals held at 16 °C. The fall in oxygen consumption rate in 7% O2 independent of changes in body temperature in tenrecs held at 16 °C is unique and not consistent with the typical hypoxic metabolic response seen in other hibernating species that depends on concomitant falls in Tb. In animals held at 28 °C, exposure to O2 levels as low as 4% and CO2 levels as high as 10% had no significant effect on V ˙ O 2 , HR, or Tb, indicative of high tolerance to both hypoxia and hypercapnia. High variation in heart rate remained between individuals in all gas compositions and at all temperatures. Tenrec Hb–O2 affinity was similar to other homeothermic placental mammals and likely does not contribute to the increased hypoxia tolerance. Ultimately, our results suggest changes in Ta dictate physiological responses to hypoxia or hypercapnia in tenrecs, responses more characteristic of reptiles than of most placental mammals. Given that numerous anatomical and physiological characteristics of tenrecs suggest that they may be representative of an ancestral placental mammal, our findings suggest the typical hypoxic metabolic response evolved later in mammalian evolution. [ABSTRACT FROM AUTHOR]

Objective: This study aimed to examine the association between hypo/hypercapnia and fluctuations in carbon dioxide (CO2) levels and severe intraventricular hemorrhage (IVH) during the initial 72 hours of life among preterm infants. Material and Methods: A retrospective study of premature infants with birth weights between 750 and 1.250 g and gestational ages of 30 weeks who required respiratory support. Blood gas measurements were collected during the first 3 days of life. Multivariate analyses were performed to assess the association between hypercapnia and carbon dioxide pressure (pCO2) fluctuations and IVH. Results: Our cohort included 376 patients with a median gestational age of 28 weeks and a median birth weight of 920 g. After controlling for gestational age and birth weight, histologic chorioamnionitis and pCO2 fluctuations remained significantly associated with severe IVH. Conclusion: Fluctuations in pCO2 over a short period may have a stronger association with severe IVH than the mere occurrence of hypo- or hypercapnia.