Sex differences during a cold-stress test in normobaric and hypobaric hypoxia: A randomized controlled crossover study

Influence of body dimensions and sex on cold-induced vasodilation

Cold-induced vasodilation (CIVD) is a physiological response characterized by cyclic vasodilation occurring within 5-10 min of cold exposure, predominantly in the fingers and toes. This study aimed to determine the roles of body dimensions, specifically surface-to-mass (SM) ratio and sex in modulating CIVD responses. Thirty-nine participants (mean ± SD age: 24 ± 3 yr; height: 174 ± 28 cm; weight: 75.3 ± 15.2 kg; 20 males & 19 females) completed a 30-min immersion of the digits in ice water while sitting in a thermoneutral room (22 °C). Skin temperature was measured continuously on the anterior pads of the index, middle, ring, and little finger to assess CIVD parameters (onset time (tonset), minimum finger temperature (Tmin), maximum finger temperature (Tmax), mean finger temperature (Tmean), and CIVDwaves). A negative relationship was observed between Tmax and SM ratio (r =  - 0.39, p = 0.001) and Tmean and SM ratio (r =  - 0.32, p = 0.001), indicating that individuals with smaller SM ratios exhibited enhanced CIVD responses. A subgroup of 7 males and 7 females with identical anthropometrics from the original cohort showed no differences between any CIVD parameter: Tmean (Males: 8.0 ± 1.9 °C; Females: 8.9 ± 1.6 °C, p = 0.36), Tmax (Males: 11.2 ± 3.1 °C; Females: 13.1 ± 1.2 °C, p = 0.16), Tmin (Males: 5.9 ± 1.4 °C; Females: 5.0 ± 1.7 °C, p = 0.31), and tonset (Males: 12.0 ± 4.4 min; Females: 9.6 ± 3.6 min, p = 0.28). Therefore, body dimensions seem to play a crucial role in modulating CIVD responses, whereas sex does not.

A protocol to simultaneously examine cardiorespiratory, cerebrovascular and neurophysiological responses inside a hypobaric chamber

We describe a protocol to examine neurophysiological (electroencephalography, EEG), cerebrovascular (ultrasound assessments of middle cerebral artery blood velocity, MCAv) and cardiorespiratory (blood pressure, oxygen saturation, end-tidal gases, respiratory rate) responses inside a hypobaric chamber. This procedure aims to standardize the methodology in experiments conducted within a hypobaric chamber such as comparing normobaric and hypobaric hypoxia. This is important because current understanding of relationships between neurophysiological activity, and cerebrovascular and cardiorespiratory responses under varying environmental conditions remains limited. This procedure combines simultaneous neurophysiological, cardiorespiratory and cerebrovascular evaluations, allowing a comprehensive understanding of electro-neurophysiological activity. Our protocol requires an hour and a half of equipment setup, 1-1.5 hours of participant set-up, and 30 minutes of experimental data collection. Since multiple simultaneous physiological recordings, including EEG in this environment, can be fraught with pitfalls, we also provide practical considerations for experimental design and recording setup. Advanced knowledge of hypobaric chamber operation is required, alongside expertise in EEG and transcranial Doppler ultrasonography. Following our procedure one will acquire simultaneous recordings of neurophysiological, cerebrovascular and cardiorespiratory data.

Hypoxia Postconditioning Attenuates Hypoxia-Induced Inflammation and Endothelial Barrier Dysfunction

INTRODUCTION

In recent years, a number of studies have demonstrated that hypoxia reoxygenation (HR) induced by ischemia postconditioning (IPC) reduces endothelial barrier dysfunction and inflammation in various models. When HR occurs, the P38 mitogen-activated protein kinase (P38 MAPK) breaks down the endothelial barrier. But no study has clearly clarified the effect of hypoxia postconditioning (HPC) on P38 MAPK in human dermal microvascular endothelial cells. Therefore, we investigated the function of HPC on P38 MAPK during HR in vitro.

METHODS

Human dermal microvascular endothelial cells were cultured in a hypoxic incubator for 8 h. Then cells were reperfused for 12 h (reoxygenation) or postconditioned by 5 min of reoxygenation and 5 min of re-hypoxia 3 times followed by 11.5 h reoxygenation. SB203580 was used as an inhibitor of P38 MAPK. Cell counting kit-8 assay kits were employed to detect cell activity. The corresponding levels of IL-6, IL-8 and IL-1β were examined via Enzyme-Linked ImmunoSorbent Assay. The endothelial barrier was evaluated using fluorescein isothiocyanate-dextran leakage assay. Western blot was used to detect claudin-5, phosphorylation of P38 MAPK (P-P38 MAPK) and P38 MAPK expression. Claudin-5 localization was studied by immunofluorescence.

RESULTS

HR induced endothelial barrier hyperpermeability, elevated inflammation levels, and increased the P-P38 MAPK. But HPC reduced cell injury and maintained the integrity of the endothelial barrier while inhibiting P-P38 MAPK and increasing expression of claudin-5. HPC redistributed claudin-5 in a continuous and linear pattern on the cell membrane.

CONCLUSIONS

HPC protects against HR induced downregulation and redistribution of claudin-5 by inhibiting P-P38 MAPK.

Acute physiological responses and muscle recovery in females: a randomised controlled trial of muscle damaging exercise in hypoxia

BACKGROUND

Studies have investigated the effects of training under hypoxia (HYP) after several weeks in a male population. However, there is still a lack of knowledge on the acute hypoxic effects on physiology and muscle recovery in a female population.

METHODS

This randomized-controlled trial aimed to investigate the acute effects of muscle damaging exercise, performed in HYP and normoxia (CON), on physiological responses and recovery characteristics in healthy females. Key inclusion criteria were recreationally active female participants between the age of 18 to 35 years without any previous surgeries and injuries, whilst key exclusion criteria were acute pain situations, pregnancy, and medication intake. The females conducted a muscle-damaging protocol, comprising 5 × 20 drop-jumps, in either HYP (FiO2: 12%) or CON (FiO2: 21%). Physiological responses, including capillary oxygenation (SpO2), muscle oxygenation (SmO2), heart rate (HR), core- (Tcore) and skin- (Tskin) temperature were assessed at the end of each exercise set. Recovery characteristics were quantified by taking venous blood samples (serum creatine-kinase [CK], C-reactive protein [CRP] and blood sedimentation rate [BSR]), assessing muscle swelling of the quadriceps femoris muscle, maximum voluntary isometric contraction (MVIC) of the knee extensor muscles, countermovement jump (CMJ) performance and muscle soreness ratings (DOMS) at 24-, 48- and 72-hrs post-exercise.

RESULTS

SpO2 (HYP: 76.7 ± 3.8%, CON: 95.5 ± 1.7%, p < 0.001) and SmO2 (HYP: 60.0 ± 9.3, CON: 73.4 ± 5.8%, p = 0.03) values were lower (p < 0.05) in HYP compared to CON at the end of the exercise-protocol. No physiological differences between HYP and CON were observed for HR, Tcore, and Tskin (all p > 0.05). There were also no differences detected for any recovery variable (CK, CRP, BSR, MVIC, CMJ, and DOMS) during the 72-hrs follow-up period between HYP and CON (all p > 0.05).

CONCLUSION

In conclusion, our results showed that muscle damaging exercise under HYP leads to reduced capillary and muscle oxygenation levels compared to normoxia with no difference in inflammatory response and muscle recovery during 72 h post-exercise.

TRIAL REGISTRATION

NCT04902924, May 26th 2021.

Microcirculatory response to cold stress test in the healthy hand

OBJECTIVE

Cold sensitivity of the fingers is common in several conditions. It has been linked to digital vasospasm, microvascular dysfunction, and neural mechanisms. This study aimed to investigate the normal digital microvascular response to a cold stress test in healthy individuals using Laser Speckle Contrast Imaging (LSCI).

METHODS

Twenty-six healthy individuals, mean age 31 (SD 9) years were included. Skin perfusion of digits II-V was measured using Laser Speckle Contrast Imaging before and after a standardized cold stress test. Changes in skin perfusion from baseline were analyzed between hands, digits, and sexes.

RESULTS

Skin perfusion was significantly (p < 0.0001) affected by cold provocation in both the cold exposed and the contralateral hands in all participants of the study. This effect was significantly different between the radial (digit II and III) and the ulnar (digit V) side of the hands (p < 0.001). There was a trend towards a larger decrease in perfusion in men (ns), and a faster recovery to baseline values in women (ns). A larger inter subject variability was seen in perfusion values in women.

CONCLUSIONS

The normal microvascular response to cold provocation may involve both centrally and regionally mediated processes. When exposing one hand to a cold stress test, the contralateral hand responds with simultaneous but smaller decreases in perfusion.

Sex comparisons in physiological and cognitive performance during hypoxic challenge

Within the tactical aviation community, human performance research lags in considering potential psychophysiological differences between male and female aviators due to little inclusion of females during the design and development of aircraft systems. A poor understanding of how male and female aviators differ with respect to human performance results in unknown potential sex differences on aeromedically relevant environmental stressors, perchance leading to suboptimal performance, safety, and health guidelines. For example, previous hypoxia studies have excluded female participants or lacked a sizeable sample to examine sex comparisons. As such, progress toward sensor development and improving hypoxia familiarization training are stunted due to limited knowledge of how individual differences, including sex, may or may not underlie hypoxia symptoms and performance impairment. Investigating sex differences bridges the gap between aerospace medicine and operational health, and addressing hypoxia is one of many facets yet to be studied. In the current study, we retrospectively examined N = 6 hypoxia studies with male-female participant samples (total, N = 189; male, n = 118; female, n = 71). We explored sex as a predictor of physiological response, sensory deficits, the severity of cognitive performance declines, and symptom manifestation via linear and binary logistic regression models. We found that the female sex predicted lower peripheral oxygen saturation and the likelihood of headache reporting in response to hypoxic challenge, yet explained little variance when combined with age and body mass index. The sensory and cognitive performance models did not converge, suggesting high intra-individual variability. Together, sex, age, and body mass index were not the most robust predictors in responses to hypoxic challenge; we cannot infer this for sensory deficits and cognitive performance within an experimentally induced hypoxic environment. The findings have implications for improving hypoxia familiarization training, monitoring sensor development, and emergency response and recovery protocols in case of a hypoxia occurrence suitable for all aircrew. We recommend continuing to elucidate the impact of sex and intrapersonal differences in hypoxia and other aeromedically relevant stressors in tactical aviation.