The Effects of Body composition (Percent Fat) On Acclimatization to Heat

1981 ◽  
Vol 25 (1) ◽  
pp. 774-778
Author(s):  
Alex Loewenthal ◽  
David J. Cochran ◽  
Michael W. Riley

Nine fully acclimatized men falling in the lean, medium and obese categories of body composition were observed during heat exposure periods for four days following acclimatization decay periods of various lengths in order to determine the effects of body composition on the decay and reinduction of acclimatization. The physiological variables taken into consideration were core temperature, “DuBois” mean skin temperature, heart rate, weight loss due to perspiration and the temperature differential between the core and surface. All of the men were subjected to an acclimatization schedule of twelve daily sessions in order to insure that they were all fully acclimatized. Three decay, or non-exposure, periods of four, eight and twelve days were each followed by four days of reinduction. It was determined that body composition does not affect the rate of decay or reinduction of acclimatization, although this parameter as well as the extent of decay and the duration of the reinduction period does affect the physiological variables monitored in this study.

1976 ◽  
Vol 40 (5) ◽  
pp. 779-785 ◽  
Author(s):  
C. H. Wyndham ◽  
G. G. Rogers ◽  
L. C. Senay ◽  
D. Mitchell

Four trained young men worked for 4 h/day at 40–50% of their maximum aerobic capacity first for 3 days at 25 degrees C db, 18 degrees C wb, and then for 10 consecutive days at 45 degrees C db, 32 degrees C wb. This portion of the study was mainly concerned with central circulatory changes during acclimatization. The central circulatory adaptation to work in heat could be divided into four distinct phases: phase I (day 1) was characterized by a progressive fall in stroke volume (SV) during heat exposure but cardiac output (CO) was maintained above control values by high heart rates. Phase II (days 2 and 3) was marked by increases in SV ande decreases in heart rate but with little change in CO from phase I. During phase III (days 4–8 of acclimatization), CO increased due to increases in SV. Phase IV (days 6–8) was associated with decreases in rectal and skin temperature towards control levels. SV and HR both decline in this phase so that CO was not elevated greatly above control levels. The results indicated that central circulatory and temperature regulating events are not casually associated in acclimatization.


2021 ◽  
Vol 42 (Supplement_1) ◽  
Author(s):  
D Aronson ◽  
Y Nitzan ◽  
S Petcherski ◽  
E Bravo ◽  
M Habib ◽  
...  

Abstract Background Current treatment of fluid retention in heart failure (HF) relies primarily on diuretics. However, adequate decongestion is not achieved in many patients. Purpose To study the feasibility and short-term performance of a novel approach to remove fluids and sodium directly from the interstitial compartment by enhancing sweat rate. Methods We used a device designed to enhance fluid and salt loss via the eccrine sweat glands. Skin temperature in the lower body was increased to 35–38°, where the slope of the relationship between temperature and sweat production is linear. With this wearable device, the sweat evaporates instantaneously, thus avoiding the awareness of perspiration. The primary efficacy endpoint was the ability to increase skin temperature to the desired range without elevating the core temperature above normal range. A secondary efficacy endpoint was a clinically meaningful hourly sweat output, defined as ≥150 mL/h. The primary safety endpoint was any procedure-related adverse events. Results We studied 6 normal subjects and 10 HF patients with clinical evidence of congestion and median NT-proBNP of 602 pg/mL [interquartile range 427 to 1719 pg/mL]. Participants underwent 3 treatment sessions of up to 4h. Skin temperature increased to a median of 37.5°C (interquartile range 37.1–37.9°C) with the core temperature remaining unchanged. The median total weight loss during treatment was 219±67 g/h (Figure) with a range of 100–338 g/h. In 77% of cases, the average sweat rate was ≥150 mL/h. Systolic (P=0.25) and diastolic (P=0.48) blood pressure and heart rate (P=0.11) remained unchanged during the procedure. There were no significant changes in renal function and no procedure-related adverse events. Conclusion Enhancing sweat rate was safe and resulted in a clinically meaningful fluid removal and weight loss. Further evaluation of this concept is warranted. FUNDunding Acknowledgement Type of funding sources: Private company. Main funding source(s): AquaPass Inc Weight loss due to sweat


2021 ◽  
Vol 5 (Supplement_1) ◽  
pp. A64-A65
Author(s):  
Kim D Huynh ◽  
Marianne C Klose ◽  
Kim Krogsgaard ◽  
Jorgen Drejer ◽  
Sarah Byberg ◽  
...  

Abstract Background: Structural damage to the hypothalamus often results in hypothalamic obesity characterized by rapid and severe weight-gain with increased risk of cardiovascular and metabolic morbidity and mortality. Currently, there are no approved or effective pharmacological treatments and conventional weight management remains largely ineffective. Objective: This RCT investigated safety and efficacy of Tesomet (co-administration of 0.5mg tesofensine and 50mg metoprolol) in hypopituitary patients with acquired hypothalamic obesity. Methods: Twenty-one (16 females) hypopituitary adults with hypothalamic obesity were randomized to Tesomet or placebo (2:1) for 24 weeks (NCT03845075). Subjects also received diet and lifestyle counselling. Primary endpoint was safety evaluated by change in heart rate, blood pressure and adverse events. Secondary endpoints included changes in anthropometric measures, body composition, corrected QT-interval and arrythmias. Results: Subjects had a median (range) age of 50 (25; 70) years and 90% had a BMI ≥30 kg/m2. Almost half (48%) had a history of craniopharyngioma, 86% had undergone pituitary/hypothalamic surgery, and 52% had irradiation therapy. All received one or more anterior pituitary hormone replacements; 52% had diabetes insipidus. In total, 18/21 subjects completed the study, one without investigational treatment. Three serious adverse events (SAE) were recorded in 2 subjects randomized to Tesomet. Adverse events were otherwise mostly mild (58%), frequently reported were sleep disturbances (62%), dry mouth (46%) and dizziness (46%), known side effects of tesofensine or metoprolol. Four subjects, two in each group, discontinued treatment. Tesomet discontinuation was secondary to anxiety (n=1) or dry mouth (n=1). No significant differences in heart rate or blood pressure were observed between the two groups. At week 24, compared to placebo (weight-loss: -0.3%), Tesomet treatment resulted in additional mean weight-loss of -6.3% (95CI [-11.3%; -1.3%], p=0.017); increase in the proportion of patients achieving >5% reduction in body weight (Tesomet 8; Placebo 1, OR 11.2 [1.0; 120.4], p=0.046); and reduction in waist circumference of -5.7cm ([-11.5; 0.1], p=0.054). Tesomet-induced weight loss was primarily correlated to a reduction in mean (SD) fat mass -5.3kg (5.3) (r2=0.9, P=0001) and to lesser extent a reduction in lean tissue mass -2.9kg (1.9) (r2=0.4, P=0.03). Treatment did not affect corrected QT-interval; mean change from placebo was -1.1ms (95CI [-16.0; 13.9], p=0.882), nor were arrythmias registered during the trial period. Conclusions: Tesomet was generally well-tolerated, did not affect heart rate, blood pressure or QTc-interval, and resulted in significant reductions in body weight compared to placebo in this cohort of hypopituitary patients with acquired hypothalamic obesity. The study was sponsored by Saniona A/S


1996 ◽  
Vol 21 (2) ◽  
pp. 90-108 ◽  
Author(s):  
Tom M. McLellan ◽  
Yukitoshi Aoyagi

The purpose of the present study was to compare the heat strain while wearing nuclear, biological, and chemical (NBC) protective clothing following a hot-wet (HW) or hot-dry (HD) heat acclimation protocol. Twenty-two males were assigned to groups HW (n = 7), HD (n = 8), or control (C, n = 7). Subjects were evaluated during continuous treadmill walking while wearing lightweight combat clothing and during intermittent exercise while wearing the NBC protective clothing. While wearing Combat clothing, greater decreases in rectal temperature (Tre), mean skin temperature [Formula: see text], and heart rate were observed for both acclimation groups. For the NBC clothing trials, lower Tre, [Formula: see text], and heart rates were observed only for group HW. The time required for Tre to increase 1.0 °C and 1.5 °C was significantly delayed for groups HW and HD. Sweat evaporation increased for HW, whereas no change was found for HD. The most significant changes in Tre, [Formula: see text], and heart rate while wearing the NBC protective clothing occur following heat acclimation that involves wearing the clothing during exercise. Key words: rectal temperature, mean skin temperature, heart rate, sweat rate


1983 ◽  
Vol 56 (3) ◽  
pp. 699-706 ◽  
Author(s):  
J. W. Aird ◽  
R. D. G. Webb ◽  
J. Hoare

Conduction velocity, absolute refractory period, and subnormal conduction period measures of the right ulnar motor nerve were obtained during a simple reaction time task. 6 young, healthy, right-arm dominant male subjects were tested following 30 min. exposure in ambient (20°C) and hot (36°C) room air conditions. Motor and premotor components of fractionated reaction time were tested on the same arm. Oral, right forearm skin and a four-site mean skin temperature were monitored. During heat exposure, forearm skin temperature increased 4.7°C and mean skin temperature 2.9°C. Oral temperature did not alter. Conduction velocity increased 11.4%, absolute refractory period decreased 22.7%, and subnormal conduction period decreased 14.1% in the hot condition. Concomitantly, a 5.2% increase in premotor reaction time and 12.2% decrease in motor reaction time were observed. Total RT did not alter significantly. It was concluded that different component parts of reaction time were differentially influenced by exposure to heat.


2012 ◽  
Vol 22 (5) ◽  
pp. 363-373 ◽  
Author(s):  
Phillip Watson ◽  
Sophie Enever ◽  
Andrew Page ◽  
Jenna Stockwell ◽  
Ronald J. Maughan

Eight young men were recruited to a study designed to examine the effect of tyrosine (TYR) supplementation on the capacity to perform prolonged exercise in a warm environment. Subjects entered the laboratory in the morning and remained seated for 1 hr before cycling to exhaustion at 70% VO2peak. Two 250-ml aliquots of a placebo (PLA ) or a TYR solution were ingested at 30-min intervals before exercise, with an additional 150 ml consumed every 15 min throughout exercise (total TYR dose: 150 mg/kg BM). Cognitive function was assessed before drink ingestion, at the end of the rest period, and at exhaustion. TYR ingestion had no effect on exercise capacity (PLA 61.4 ± 13.7 min, TYR 60.2 ± 15.4 min; p = .505). No differences in heart rate (p = .380), core temperature (p = .554), or weighted mean skin temperature (p = .167) were apparent between trials. Ingestion of TYR produced a marked increase in serum TYR concentrations (+236 ± 46 μmol/L; p < .001), with this difference maintained throughout exercise. No change was apparent during the PLA trial (p = .924). Exercise caused an increase in error rate during the complex component of the Stroop test (p = .034), but this response was not influenced by the drink ingested. No other component of cognitive function was altered by the protocol (all p > .05). Ingestion of a TYR solution did not influence time to exhaustion or several aspects of cognitive function when exercise was undertaken in a warm environment.


2007 ◽  
Vol 103 (4) ◽  
pp. 1257-1262 ◽  
Author(s):  
Thad E. Wilson ◽  
Charity L. Sauder ◽  
Matthew L. Kearney ◽  
Nathan T. Kuipers ◽  
Urs A. Leuenberger ◽  
...  

Skin-surface cooling elicits a pronounced systemic pressor response, which has previously been reported to be associated with peripheral vasoconstriction and may not fully account for the decrease in systemic vascular conductance. To test the hypothesis that whole body skin-surface cooling would also induce renal and splanchnic vasoconstriction, 14 supine subjects performed 26 skin-surface cooling trials (15–18°C water perfused through a tube-lined suit for 20 min). Oral and mean skin temperature, heart rate, stroke volume (Doppler ultrasound), mean arterial blood pressure (MAP), cutaneous blood velocity (laser-Doppler), and mean blood velocity of the brachial, celiac, renal, and superior mesenteric arteries (Doppler ultrasound) were measured during normothermia and skin-surface cooling. Cardiac output (heart rate·stroke volume) and indexes of vascular conductance (flux or blood velocity/MAP) were calculated. Skin-surface cooling increased MAP ( n = 26; 78 ± 5 to 88 ± 5 mmHg; mean ± SD) and decreased mean skin temperature ( n = 26; 33.7 ± 0.7 to 27.5 ± 1.2°C) and cutaneous ( n = 12; 0.93 ± 0.68 to 0.36 ± 0.20 flux/mmHg), brachial ( n = 10; 32 ± 15 to 20 ± 12), celiac ( n = 8; 85 ± 22 to 73 ± 22 cm·s−1·mmHg−1), superior mesenteric ( n = 8; 55 ± 16 to 48 ± 10 cm·s−1·mmHg−1), and renal ( n = 8; 74 ± 26 to 64 ± 20 cm·s−1·mmHg−1; all P < 0.05) vascular conductance, without altering oral temperature, cardiac output, heart rate, or stroke volume. These data identify decreases in vascular conductance of skin and of brachial, celiac, superior mesenteric, and renal arteries. Thus it appears that vasoconstriction in both peripheral and visceral arteries contributes importantly to the pressor response produced during skin-surface cooling in humans.


1965 ◽  
Vol 20 (2) ◽  
pp. 278-282 ◽  
Author(s):  
Leo C. Senay ◽  
Margaret L. Christensen

Resting subjects were exposed for 12 hr to 43 C dry bulb, 28 C wet bulb, with and without rehydration. During dehydration, average weighted cutaneous opacity pulse amplitudes decreased 19.5%. An apparent relationship between calculated stroke volume and cutaneous pulse amplitudes existed. A 26% increase in heart rate offset decreases in perfusion per beat and probably contributed to a rise in diastolic pressure. Increases in skin temperature paralleled those of oral temperatures. In most subjects evaporative rates were slightly lower during dehydration. Certain dehydrating subjects maintained sweat rates at control levels but this did not prevent an increase in both oral and skin temperatures. Failure of temperature regulation in these experiments does not appear to be due to a decrease in heat transport or evaporation but rather to a lack of responsiveness of the sudomotor and vasomotor systems to increases in body temperature. Reasons for the temperature rise appear complex. evaporative weight loss; heat transport; skin temperature; temperature regulation Submitted on July 22, 1964


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