Progressive dry to humid hyperthermia alters exercise cerebral blood flow

Cardiovascular autonomic modulation during passive heating protocols: a systematic review

Objective.To conduct a systematic review of the possible effects of passive heating protocols on cardiovascular autonomic control in healthy individuals.Approach.The studies were obtained from MEDLINE (PubMed), LILACS (BVS), EUROPE PMC (PMC), and SCOPUS databases, simultaneously. Studies were considered eligible if they employed passive heating protocols and investigated cardiovascular autonomic control by spontaneous methods, such as heart rate variability (HRV), systolic blood pressure variability (SBPV), and baroreflex sensitivity (BRS), in healthy adults. The revised Cochrane risk-of-bias tool (RoB-2) was used to assess the risk of bias in each study.Main results.Twenty-seven studies were included in the qualitative synthesis. Whole-body heating protocols caused a reduction in cardiac vagal modulation in 14 studies, and two studies reported both increased sympathetic modulation and vagal withdrawal. Contrariwise, local-heating protocols and sauna bathing seem to increase cardiac vagal modulation. A reduction of BRS was reported in most of the studies that used whole-body heating protocols. However, heating effects on BRS remain controversial due to methodological differences among baroreflex analysis and heating protocols.Significance.Whole-body heat stress may increase sympathetic and reduce vagal modulation to the heart in healthy adults. On the other hand, local-heating therapy and sauna bathing seem to increase cardiac vagal modulation, opposing sympathetic modulation. Nonetheless, further studies should investigate acute and chronic effects of thermal therapy on cardiovascular autonomic control.

The Evaluation of Physiological Index Changes and Safety Work of Female Medical Staff With Different Medical Protection Standards in the Ward of COVID-19

Background

Effective personal protective equipment (PPE) contribute to the prevention of COVID-19 infection. However, it is necessary to evaluate the potential risk of different medical protections in the isolation ward of COVID-19.

Objectives

We aimed to explore the dynamics in physiological indexes of medical staff under primary and secondary PPE in the isolation ward of COVID-19 and provide the scientific basis for determining the safe work strategy.

Materials and Methods

In this study, 30 female nurses were selected to simulate medical work under the primary or secondary PPE, respectively. The oral temperature, axillary temperature, heart rate, respiratory rate, blood oxygen saturation, and blood pressure were measured and recorded every 20 min. The subjective adverse symptoms were recorded every 30 min. The blood glucose and weight of the individuals were measured and recorded before and after the trial.

Results

The results indicated that the median trial persistence time in the participants with moderate-intensity work wearing the secondary PPE (70.0 min) was much lower than that with moderate-intensity work wearing the primary PPE (180 min) and with light-intensity work wearing the primary PPE (110 min; p < 0.05). Importantly, the heart rate, oral/axillary temperature, and respiratory rate of physiological indexes of the participants under moderate-intensity work wearing the secondary PPE increased significantly faster than the primary PPE (p < 0.001), while blood oxygen saturation decreased significantly faster than the primary PPE (p < 0.001). In addition, the proportions of subjective adverse symptoms (such as dry mouth, dizziness, palpitations, and anhelation) were much higher than primary PPE (p < 0.001). The average sweat volume and blood glucose consumption of participants under moderate-intensity work wearing primary PPE were higher than secondary PPE (p < 0.001).

Conclusion

The combination of an exacerbated workload and secondary PPE worn by COVID-19 healthcare workers increases the change in physiological indicators, and in some cases the adverse symptoms, which can affect and even suspend their medical work. For any medical institution, there is room for improvement in terms of bioethics of a "Job Well Done" to reduce the risks of medical activities under secondary PPE.

Thermal discomfort in healthcare workers during the COVID-19 pandemic

Introduction:

Due to the COVID-19 pandemic, healthcare workers are now required to use additional personal protective equipment (PPEs) to protect themselves against the virus. That led to an increased clothing insulation which is negatively affecting the perceived healthcare workers’ thermal sensation.

Objectives:

While demonstrating through software simulations the potential level of thermal discomfort healthcare workers involved in the COVID-19 emergency can be subjected to, this work aims at identifying measures to improve thermal sensation perception and acceptable thermal conditions for medical personnel.

Methods:

After having obtained the insulation values of individual clothing used by staff during COVID-19 emergency through the use of a thermal well-being evaluation software, the Fanger indexes (PMV - Predicted Mean Vote and PPD - Predicted Percentage of Dissatisfied) were calculated in order to estimate staff satisfaction to microclimatic conditions.

Results:

The use of COVID-19 additional PPEs with an air temperature equal to 22 °C (normally considered optimal) brings the PMV index equal to 0.6, which corresponds to 11.8 % being unsatisfied (PPD) due to perceived heat.

Discussion:

The use of additional protective devices significantly increases the clothing insulation level, facilitating the onset of conditions of thermal discomfort in the health workers. Workers engaged in the execution of nasopharyngeal swabs were most affected by the summer weather conditions and certainly represent the most critical category, for which it would be recommended to implement a higher turnover of service to reduce individual exposure time and consequent discomfort.

Sex Differences in Thermal Comfort, Perception, Feeling, Stress and Focus During Exercise Hyperthermia

It is unclear whether men and women perceive thermal stress differently when changes in intestinal temperature (ΔTin) and metabolic heat production (MHprod) are matched between sexes during exercise hyperthermia. This study tested the hypothesis that females have enhanced sensitivity to comfort and perception of thermal stress during exercise hyperthermia in these conditions. We had 22 healthy active adults (11 males, 11 females; M age = 22.4 years, SD = 4.9; M height = 169 cm, SD = 7.6; M weight = 68.3 kg, SD = 13) exercise in random order, separated by at least three days at similar MHprod (M = 7.0 W/kg, SD = 1.5; p = 0.32) for 60 minutes on a cycle ergometer in cool (M = 24.0⁰C, SD = 0.0; M = 14.4%Rh, SD = 3.6) and hot (M = 42.3°C, SD = 0.2; M = 10-60%Rh) environments with a progressive increase in humidity conditions. We measured ΔTin, and thermal stress indices for sensation (TS), comfort (TC), pleasantness (TP), and stickiness (S), feeling (FS scale), stress (visual analogue stress scale, VAS), focus (F) and felt arousal (FAS scale). We examined environmental conditions as wet bulb globe temperatures (WBGT). Males and females had similar increases in ΔTin (ME: WBGT; p < 0.0001), and both groups reported increased TS and TC and decreased TP (ME: WBGT, p ≤ 0.01). However, females reported that TS, TC, and TP, felt hotter overall, more uncomfortable, and more unpleasant, compared to males (ME: Sex; p < 0.04). Overall, females felt worse and were more stressed compared to males (ME: Sex; p ≤ 0.05). Females also reported greater internal focus as WBGT increased compared to males (I: WBGT × Sex; p < 0.003). Knowing that females perceive thermal stress during exercise hyperthermia to be hotter, more uncomfortable, more unpleasant, and more stressful compared to males can help coaches/trainers plan different exercise routines for exercisers of both sexes.

Sex difference in cerebral blood flow velocity during exercise hyperthermia

INTRODUCTION

Cerebral blood flow and thermal perception during physical exercise under hyperthermia conditions in females are poorly understood. Because sex differences exist for blood pressure control, resting middle cerebral artery velocity (MCA_Vmean), and pain, we tested the hypothesis that females would have greater reductions in MCAv_mean and increased thermal perceptual strain during exercise hyperthermia compared to males.

METHODS

Twenty-two healthy active males and females completed 60 min of matched exercise metabolic heat production in a 1) control cool (24.0 ± 0.0 °C; 14.4 ± 3.4% Rh) and 2) hot (42.3 ± 0.3 °C; 28.4 ± 5.2% Rh) conditions in random order, separated by at least 3 days while MCAv_mean, thermal comfort, and preference was obtained during the exercise.

RESULTS

Compared to 36 °C mean body temperature (M^bt), as hyperthermia increased to 39 °C Mbt, females had a greater reduction in absolute (MCAv_mean), and relative change (%Δ MCAv_mean) and conductance (%Δ MCAv_mean conductance) in MCA_Vmean compared to males (Interaction: Temperature x Sex, P ≤ 0.002). During exercise in cool conditions, absolute and conductance MCAv_mean was maintained from rest through exercise; however, females had greater MCA_Vmean compared to males (Main effect: Sex, P < 0.0008). We also found disparities in females' perceptual thermal comfort and thermal preference. These differences may be associated with a greater reduction in partial pressure of end-tidal CO₂, and different cardiovascular and blood pressure control to exercise under hyperthermia.

CONCLUSIONS

In summary, females exercise cerebral blood flow velocity is reduced to a greater extent (25% vs 15%) and the initial reduction occurs at lower hyperthermia mean body temperatures (~38 °C vs ~39 °C) and are under greater thermal perceptual strain compared to males.