To mitigate rises in core temperature >1°C, the American Conference of Governmental Industrial Hygienists (ACGIH) recommends upper limits for heat stress (action limit values ALV), defined by ...wet-bulb globe temperature (WBGT) and a worker's metabolic rate. However, these limits are based on data from young men and are assumed to be suitable for all workers, irrespective of age or health status. We therefore explored the effect of aging, type 2 diabetes (T2D), and hypertension (HTN) on tolerance to prolonged, moderate-intensity work above and below these limits.
Core temperature and heart rate were assessed in healthy, heat unacclimatized young (18-30 yr, n = 13) and older (50-70 yr) men (n = 14) and heat unacclimatized older men with T2D (n = 10) or HTN (n = 13) during moderate-intensity (metabolic rate: 200 W·m-2) walking for 180 min (or until termination) in environments above (28°C and 32°C WBGT) and below (16°C and 24°C WBGT) the ALV for continuous work at this intensity (25°C WBGT).
Work tolerance in the 32°C WBGT was shorter in men with T2D (median IQR; 109 91-173 min; P = 0.041) and HTN (120 65-170 min; P = 0.010) compared with healthy older men (180 133-180 min). However, aging, T2D, and HTN did not significantly influence (i) core temperature or heart rate reserve, irrespective of WBGT; (ii) the probability that core temperature exceeded recommended limits (>1°C) under the ALV; and (iii) work duration before core temperature exceeded recommended limits (>1°C) above the ALV.
These findings demonstrate that T2D and HTN attenuate tolerance to uncompensable heat stress (32°C WBGT); however, these chronic diseases do not significantly impact thermal and cardiovascular strain, or the validity of ACIGH recommendations during moderate-intensity work.
Summary
Objective
Augmented brown adipose tissue (BAT) mass and activity lead to higher basic metabolic rate which is beneficial against obesity. Our aim was to investigate whether habitual (i.e. ...usual weekly participation) physical activity is linked with BAT activity and mass in humans, in a group of patients undergoing 18F‐fluorodeoxyglucose positron emission tomography/computed tomography (PET/CT) scanning.
Design
Cross‐sectional study.
Patients
Forty patients with cancer 26 male; 14 female; age 52·7 ± 17·5; body mass index (BMI) 26·4 ± 4·5.
Measurements
Patients completed the ‘usual week’ form of the International Physical Activity Questionnaire and underwent assessment of BAT activity/mass via 18F‐fluorodeoxyglucose PET/CT.
Results
We detected a significant association between habitual physical activity (METs‐minute/week) and BAT activity normalized by body weight (BW) (τ = 0·28, P = 0·02), body surface area (BSA) (τ = 0·29, P = 0·02) and lean body mass (LBM) (τ = 0·38, P = 0·002). We also found a significant negative relationship between BMI and BAT activity normalized by BW (τ = −0·30, P = 0·006), BSA (τ = −0·31, P = 0·004) and LBM (τ = −0·45, P = 0·001) as well as a significant negative relationship between age and BAT activity normalized by LBM (τ = −0·28, P = 0·01). The results also indicate significant differences between low/moderate/high levels of habitual physical activity and BAT activity (P < 0·05). Moreover, BAT activity was different across the BMI categories (normal/overweight/obese) in both sexes (P < 0·05). Finally, BAT activity was greater in women than in men (P < 0·05).
Conclusions
Increased participation in habitual physical activity is associated with higher BAT activity. Moreover, individuals with normal BMI demonstrate higher BAT activity compared to overweight and obese individuals. Finally, age is inversely linked with BAT activity, while women demonstrate higher BAT activity than men.
The brain's temperature measurements (T
) in patients with severe brain damage are important, in order to offer the optimal treatment. The purpose of this research is the creation of mathematical ...models for the T
's prediction, based on the temperatures in the bladder (T
), femoral artery (T
), ear canal (T
), and axilla (T
), without the need for placement of intracranial catheter, contributing significantly to the research of the human thermoregulatory system.The research involved 18 patients (13 men and 5 women), who were hospitalized in the adult intensive care units (ICU) of Larissa's two hospitals, with severe brain injury. An intracranial catheter with a thermistor was used to continuously measure T
and other parameters. The T
's measurements, and simultaneously one or more of T
, T
, T
, and T
, were recorded every 1 h.To create T
predicting models, the data of each measurement was separated into (a) model sample (measurements' 80%) and (b) validation sample (measurements' 20%). Multivariate linear regression analysis demonstrated that it is possible to predict brain's temperature (PrT
), using independent variables (R
was T
= 0.73, T
= 0.80, T
= 0.27, and T
= 0.17, p < 0.05). Significant linear associations were found, statistically, and no difference in means between T
and PrT
of each prediction model. Also, the 95% limits of agreement and the percent coefficient of variation showed sufficient agreement between the T
and PrT
in each prediction model.In conclusion, brain's temperature prediction models based on T
, T
, T
, and T
were successful. Its determination contributes to the improvement of clinical decision-making.
To mitigate excessive rises in core temperature (>1°C) in non heat-acclimatized workers, the American Conference of Governmental Industrial Hygienists (ACGIH) provide heat stress limits (Action Limit ...Values; ALV), defined by the wet-bulb globe temperature (WBGT) and a worker's metabolic rate. However, since these limits are based on data from men, their suitability for women remains unclear. We therefore assessed core temperature and heart rate in men (n=19; body surface area-to-mass ratio: 250 (SD 17) cm2/kg) and women (n=15; body surface area-to-mass ratio: 268 (SD 24) cm2/kg) aged 18-45 years during 180-min walking at a moderate metabolic rate (200 W/m2) in WBGTs below (16 and 24°C) and above (28 and 32°C) ACGIH ALV. Sex did not significantly influence (i) rises in core temperature, irrespective of WBGT, (ii) the proportion of participants with rises in core temperature >1°C in environments below ACGIH limits, and (iii) work duration before rises in core temperature exceeded 1°C or volitional termination in environments above ACGIH limits. Although further studies are needed, these findings indicate that for the purpose of mitigating rises in core temperature exceeding recommended limits (>1°C), ACGIH guidelines have comparable effectiveness in non heat-acclimatized men and women when working at a moderate metabolic rate. Novelty points • Sex did not appreciably influence thermal strain nor the proportion of participants with core temperatures exceeding recommended limits. • Sex did not significantly influence tolerance to uncompensable heat stress • Despite originating from data obtained in only men, current occupational heat stress guidance offered comparable effectiveness in men and women.
Rationale
Monitoring physiological strain is recommended to safeguard workers during heat exposure, but is logistically challenging. The perceptual strain index (PeSI) is a subjective estimate ...thought to reflect the physiological strain index (PSI) that requires no physiological monitoring. However, sex is known to influence perceptions of heat stress, potentially limiting the utility of the PeSI.
Objectives
The objective of this study was to assess whether sex modifies the relationship between PeSI and PSI.
Methods
Thirty‐four adults (15 females) walked on a treadmill (moderate intensity; ~200 W/m2) for 180 min or until termination (volitional fatigue, rectal temperature ≥39.5°C) in 16°C, 24°C, 28°C, and 32°C wet‐bulb globe temperatures. Rectal temperature and heart rate were recorded to calculate PSI (0–10 scale). Rating of perceived exertion and thermal sensation were recorded to calculate PeSI (0–10 scale). Relationships between PSI and PeSI were evaluated via linear mixed models. Mean bias (95% limits of agreement LoA) between PSI and PeSI was assessed via Bland–Altman analysis. Mean absolute error between measures was calculated by summing absolute errors between the PeSI and the PSI and dividing by the sample size.
Findings
PSI increased with PeSI (p < 0.01) but the slope of this relation was not different between males and females (p = 0.83). Mean bias between PSI and PeSI was small (−0.4 points), but the 95% LoA (−3.5 to 2.7 points) and mean absolute error were wide (1.3 points).
Impact
Our findings indicate that sex does not appreciably impact the agreement between the PeSI and PSI during simulated occupational heat stress. The PeSI is not a suitable surrogate for the PSI in either male or female workers.
Athletes and military personnel are often expected to compete and work in hot and/or humid environments, where decrements in performance and an increased risk of exertional heat illness are ...prevalent. A physiological strategy for reducing the adverse effects of heat stress is to acclimatise to the heat.
The aim of this systematic review was to quantify the effects of relocating to a hotter climate to undergo heat acclimatisation in athletes and military personnel.
Studies investigating the effects of heat acclimatisation in non-acclimatised athletes and military personnel via relocation to a hot climate for < 6 weeks were included.
MEDLINE, SPORTDiscus, CINAHL Plus with Full Text and Scopus were searched from inception to June 2022.
A modified version of the McMaster critical review form was utilised independently by two authors to assess the risk of bias.
A Bayesian multi-level meta-analysis was conducted on five outcome measures, including resting core temperature and heart rate, the change in core temperature and heart rate during a heat response test and sweat rate. Wet-bulb globe temperature (WBGT), daily training duration and protocol length were used as predictor variables. Along with posterior means and 90% credible intervals (CrI), the probability of direction (Pd) was calculated.
Eighteen articles from twelve independent studies were included. Fourteen articles (nine studies) provided data for the meta-analyses. Whilst accounting for WBGT, daily training duration and protocol length, population estimates indicated a reduction in resting core temperature and heart rate of - 0.19 °C 90% CrI: - 0.41 to 0.05, Pd = 91% and - 6 beats·min
90% CrI: - 16 to 5, Pd = 83%, respectively. Furthermore, the rise in core temperature and heart rate during a heat response test were attenuated by - 0.24 °C 90% CrI: - 0.67 to 0.20, Pd = 85% and - 7 beats·min
90% CrI: - 18 to 4, Pd = 87%. Changes in sweat rate were conflicting (0.01 L·h
90% CrI: - 0.38 to 0.40, Pd = 53%), primarily due to two studies demonstrating a reduction in sweat rate following heat acclimatisation.
Data from athletes and military personnel relocating to a hotter climate were consistent with a reduction in resting core temperature and heart rate, in addition to an attenuated rise in core temperature and heart rate during an exercise-based heat response test. An increase in sweat rate is also attainable, with the extent of these adaptations dependent on WBGT, daily training duration and protocol length.
CRD42022337761.
We examined the effect of thermal balance perturbation on cold-induced vasodilation through a dynamic A-B-A-B design applying heat (condition A) and cold (condition B) to the body's core, while the ...hand is exposed to a stable cold stimulus. Fifteen healthy adults (8 men, 7 women) volunteered. Applications of heat and cold were achieved through water immersions in two tanks maintained at 42 and 12 degrees C water temperature, respectively, in an A-B-A-B fashion. Throughout the experiment, the participants' right hand up to the ulnar styloid process was placed inside a temperature-controlled box set at 0 degrees C air temperature. Results demonstrated that cold-induced vasodilation occurred only during condition B and at times when body heat content was decreasing but rectal temperature had not yet dropped to baseline levels. Following the occurrence of all cold-induced vasodilation events, rectal temperature was reduced, and the phenomenon ceased when rectal temperature fell below baseline. Heart rate variability data obtained before and during cold-induced vasodilation demonstrated a shift of autonomic interaction toward parasympathetic dominance, which, however, was attributed to a sympathetic withdrawal. Receiver operating characteristics curve analyses demonstrated that the cold-induced vasodilation onset cutoff points for rectal temperature change and finger temperature were 0.62 and 16.76 degrees C, respectively. It is concluded that cold-induced vasodilation is a centrally originating phenomenon caused by sympathetic vasoconstrictor withdrawal. It is dependent on excess heat, and it may be triggered by excess heat with the purpose of preserving thermal balance.
Aging impairs heat loss, but when does it matter? Stapleton, Jill M; Poirier, Martin P; Flouris, Andreas D ...
Journal of applied physiology (1985),
02/2015, Letnik:
118, Številka:
3
Journal Article
Recenzirano
Odprti dostop
Aging is associated with an attenuated physiological ability to dissipate heat. However, it remains unclear if age-related impairments in heat dissipation only occur above a certain level of heat ...stress and whether this response is altered by aerobic fitness. Therefore, we examined changes in whole body evaporative heat loss (HE) as determined using whole body direct calorimetry in young (n = 10; 21 ± 1 yr), untrained middle-aged (n = 10; 48 ± 5 yr), and older (n = 10; 65 ± 3 yr) males matched for body surface area. We also studied a group of trained middle-aged males (n = 10; 49 ± 5 yr) matched for body surface area with all groups and for aerobic fitness with the young group. Participants performed intermittent aerobic exercise (30-min exercise bouts separated by 15-min rest) in the heat (40°C and 15% relative humidity) at progressively greater fixed rates of heat production equal to 300 (Ex1), 400 (Ex2), and 500 (Ex3) W. Results showed that HE was significantly lower in middle-aged untrained (Ex2: 426 ± 34; and Ex3: 497 ± 17 W) and older (Ex2: 424 ± 38; and Ex3: 485 ± 44 W) compared with young (Ex2: 472 ± 42; and Ex3: 558 ± 51 W) and middle-aged trained (474 ± 21; Ex3: 552 ± 23 W) males at the end of Ex2 and Ex3 (P < 0.05). No differences among groups were observed during recovery. We conclude that impairments in HE in older and middle-aged untrained males occur at exercise-induced heat loads of ≥400 W when performed in a hot environment. These impairments in untrained middle-aged males can be minimized through regular aerobic exercise training.
Introduction
The recommended treatment for exertional heat stroke is immediate, whole-body immersion in < 10 °C water until rectal temperature (T
re
) reaches ≤ 38.6 °C. However, real-time T
re
...assessment is not always feasible or available in field settings or emergency situations. We defined and validated immersion durations for water temperatures of 2–26 °C for treating exertional heat stroke.
Methods
We compiled data for 54 men and 18 women from 7 previous laboratory studies and derived immersion durations for reaching 38.6 °C T
re
. The resulting immersion durations were validated against the durations of cold-water immersion used to treat 162 (98 men; 64 women) exertional heat stroke cases at the Falmouth Road Race between 1984 and 2011.
Results
Age, height, weight, body surface area, body fat, fat mass, lean body mass, and peak oxygen uptake were weakly associated with the cooling time to a safe T
re
of 38.6 °C during immersions to 2–26 °C water (
R
2
range: 0.00–0.16). Using a specificity criterion of 0.9, receiver operating characteristics curve analysis showed that exertional heat stroke patients must be immersed for 11–12 min when water temperature is ≤ 9 °C, and for 18–19 min when water temperature is 10–26 °C (Cohen’s Kappa: 0.32–0.75,
p
< 0.001; diagnostic odds ratio: 8.63–103.27).
Conclusion
The reported immersion durations are effective for > 90% of exertional heat stroke patients with pre-immersion T
re
of 39.5–42.8 °C. When available, real-time T
re
monitoring is the standard of care to accurately diagnose and treat exertional heat stroke, avoiding adverse health outcomes associated with under- or over-cooling, and for implementing cool-first transport second exertional heat stroke policies.
Ambient temperature can affect the survival rate of humans. Studies have shown a relationship between ambient temperature and mortality rate in hot and cold environments. This effect of ambient ...temperature on mortality seems to be more pronounced in older people. The aim of this study is to examine the effects of thermal stress on cardiovascular mortality and the associated relative risk per degree Celsius in Greek individuals ≥70 years old. Mortality data 1999-2012 were matched with the midday temperature. The present study found a higher circulatory mortality when ambient temperature is below or above the temperature range 6 to 39 °C.
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