Exercise thermoregulation in men after 1 and 24-hours of 6 degrees head-down tilt

BACKGROUND: Exercise thermoregulation is dependent on heat loss by increased skin blood flow (convective and conductive heat loss) and through enhanced sweating (evaporative heat loss). Reduction of plasma volume (PV), increased plasma osmolality, physical deconditioning, and duration of exposure to simulated and actual microgravity reduces the ability to thermoregulate during exercise. HYPOTHESIS: We hypothesized that 24 h of head down tilt (HDT24) would alter thermoregulatory responses to a submaximal exercise test and result in a higher exercise rectal temperature (Tre) when compared with exercise Tre after 1 h of head down tilt (HDT1). METHODS: Seven men (31+/-SD 6 yr, peak oxygen uptake (VpO2peak) of 44+/-6 ml x kg(-1) x min(-1)) were studied during 70 min of supine cycling at 58+/-SE 1.5% VO2peak at 22.0 degrees C Tdb and 47% rh. RESULTS: Relative to pre-tilt sitting chair rest data, HDT1 resulted in a 6.1+/-0.9% increase and HDT24 in a 4.3+/-2.3% decrease in PV (delta = 10.4% between experiments, p<0.05) while plasma osmolality remained unchanged (NS). Pre-exercise Tre was elevated after HDT24 (36.71 degrees C +/-0.06 HDT1 vs. 36.93 degrees C+/-0.11 HDT24, p<0.05). The 70 min of exercise did not alter this relationship (p<0.05) with respective end exercise increases in Tre to 38.01 degrees C and 38.26 degrees C (degrees = 1.30 degrees C (HDT1) and 1.33 degrees C (HDT24)). While there were no pre-exercise differences in mean skin temperature (Tsk), a significant (p<0.05) time x treatment interaction occurred during exercise: after min 30 in HDT24 the Tsk leveled off at 31.1 degrees C, while it continued to increase reaching 31.5 degrees C at min 70 in HDT1. A similar response (NS) occurred in skin blood velocity. Neither local sweating rates nor changes in body weight during exercise of -1.63+/-0.24 kg (HDT1) or - 1.33+/-0.09 kg (HDT24) were different (NS) between experiments. CONCLUSION: While HDT24 resulted in elevated pre-exercise Tre, reduced PV, attenuation of Tsk and skin blood velocity during exercise, the absolute increase in exercise Tre was not altered. But if sweat rate and cutaneous vascular responses were similar at different core temperatures (unchanged thermoregulation), the Tre offset could have been caused by the HDT-induced hypovolemia.     

Eighty-four hours of sustained operations alter thermoregulation during cold exposure

PURPOSE; This study examined the effects of short-term (3.5 d) sustained military operations (SUSOPS) on thermoregulatory responses to cold stress. METHODS: Ten men (22.8 +/- 1.4 yr) were assessed during a cold-air test (CAT) after a control week (control) and again after an 84-h SUSOPS (sleep = 2 h.d (-1), energy intake = approximately 1650 kcal.d(-1), and energy expenditure = approximately 4500 kcal.d(-1). CAT consisted of a resting subject (seminude) being exposed to an ambient temperature ramp from 25 degrees C to 10 degrees C during the initial 30 min of CAT, with the ambient temperature then remaining at 10 degrees C for an additional 150 min. RESULTS: SUSOPS decreased (P< 0.05) body weight, % body fat, and fat-free mass by 3.9 kg, 1.6%, and 1.8 kg, respectively. During CAT, rectal temperature decreased to a greater extent (P< 0.05) after SUSOPS (0.52 +/- 0.09 degrees C) versus control (0.45 +/- 0.12 degrees C). Metabolic heat production was lower (P< 0.05) after SUSOPS at min 30 (55.4 +/- 3.3 W.m (-2)) versus control (66.9 +/- 4.4 W.m(-2)). Examination of the mean body temperature-metabolic heat production relationship indicated that the threshold for shivering was lower (P< 0.05) after SUSOPS (34.8 +/- 0.2 degrees C) versus control (35.8 +/- 0.2 degrees C). Mean weighted skin temperatures ( degrees C) were lower during the initial 1.5 h of CAT in SUSOPS versus control. Heat debt was similar between trials. CONCLUSION: These results indicate that sustained (84-h) military operations leads to greater declines in core temperature, due to either a lag in the initial shivering response or heat redistribution secondary to an insulative acclimation.     

Physical exertion tolerance after water immersion

Before and after 24-hour water immersion test subjects performed a submaximal workload on a bicycle ergometer. Changes in their hematocrit, circulating plasma volume and fluid balance were compared with those during immersion. As a result, the test subjects were subdivided into two groups. For one group the workload was very hard; adaptation to immersion was accompanied by significant renal losses of fluid from the intra- and extravascular space. The bicycle ergometry test after immersion demonstrated a decrease of exercise tolerance combined with circulatory disorders. The other group showed a higher exercise tolerance; after immersion exercise tolerance remained high at the expense of the reserves that maintained optimal blood supply to the working muscles.     

Effect of longitudinal physical training and water immersion on orthostatic tolerance in men

To test the hypothesis that moderately intense physical training has no effect on orthostasis, orthostatic and fluid-electrolyte-endocrine responses to 60 degrees head-up tilt were compared before and after 6 h of water immersion (34.5 +/- 0.1 degrees C) up to the neck following 6 months of exercise training. During the tilt test the five male subjects (27-42 years) each wore a lower-body positive-pressure suit (MAST-111A antishock trousers). The tilt procedure consisted of a 40-min supine control period (suit deflated), followed by a maximum 90-min tilt period (suit inflated to 50 +/- 5 mm Hg for 30 min, then deflated for 60 min or until presyncope). The mean +/- S.E. pretraining cycle ergometer peak VO2 was 3.20 +/- 0.14 L.min-1 (39 +/- 2 ml.min-1.kg-1), 3.36 +/- 0.27 L.min-1 (42 +/- 4 ml.min-1.kg-1) after 3 months (N.S.), and increased by 18% to 3.78 +/- 0.36 L.min-1 (48 +/- 5 ml.min-1.kg-1, +22%, p less than 0.05) posttraining. During pretraining, water immersion tilt tolerance decreased from 74 +/- 16 min before to 34 +/- 9 min (delta = 40 min, p less than 0.05) after immersion. During posttraining, water immersion tilt tolerance decreased similarly from 74 +/- 16 min preimmersion to 44 +/- 13 min (delta = 30 min, p less than 0.05) postimmersion (74 vs. 74 min, N.S.; 34 vs. 44 min, N.S.).(ABSTRACT TRUNCATED AT 250 WORDS)     

Human thermoregulation after atropine and/or pralidoxime administration

The effects of intramuscular saline (control), atropine (2 mg), and/or pralidoxime (600 mg) on heat exchange was evaluated in four healthy males during seated, cycle exercise (55% Vo2 peak) in a temperate environment (Ta = 30.3 degrees C, Pw = 1.0 kPa). Esophageal (Tes), rectal (Tre), and mean skin temperatures (Tsk), and chest and forearm sweating (ms) were continuously measured. Skin blood flow (FBF) from the forearm was measured twice each minute by venous occlusion plethysmography. Whole body sweating was calculated from weight changes. The expected result of atropine injection, decreased eccrine sweating (-60%, p less than 0.05) and elevated esophageal (+0.4 degree C, p less than 0.05) and skin temperatures (+2.1 degrees C, p less than 0.05) was observed relative to control. Heart rate (+28 b X min-1) and FBF (+9 ml X 100 ml-1 X min-1) were higher after atropine. Pralidoxime, in general, did not affect the core and skin temperature responses to the exercise differently from control; however, a slightly elevated FBF (+3 ml X 100 cc-1 X min-1, 33%) compensated for the reduction in whole body sweating (-45%, p less than 0.05] that we observed. The combination of the drugs resulted in significantly higher esophageal (0.4 degree C) and skin (0.9 degree C) temperatures than atropine alone, as has been previously shown. The thermoregulatory disadvantage of inhibited sweating by atropine was partially compensated for by enhanced skin blood flow in this environment where Ta less than Tsk. Pralidoxime was shown to decrease whole body sweating, by a mechanism as yet unexplained.     

肢体爆炸伤海水浸泡后皮肤软组织的病理改变

目的探讨肢体爆炸伤海水浸泡后皮肤软组织的病理变化特点，为海战伤中采用组织移植等修复方法处理伤口提供理论依据。方法选用纸壳爆破雷管炸伤家兔后肢，将致伤家兔分别置于海水中浸泡30min和1h，并分别在浸泡后2、6、12h取材，肉眼、光镜观察组织形态变化，并与单纯爆炸伤和淡水浸泡组进行比较。结果肢体爆炸伤海水浸泡后皮肤损伤程度、范围以及炎症反应明显重于单纯火器伤组；浸泡时间越长，组织损伤越重；海水浸泡后嗜酸性粒细胞明显增多，与单纯火器伤组和淡水浸泡组有明显区别。结论爆炸伤后海水浸泡不但加重了皮肤组织的继发损伤，而且伤口全部基染，并司见大量嗜酸性粒细胞。本研究结果对海战中研究伤口修复的方法有一定的指导意义。     

Plasma volume and endocrine responses to water immersion with intermittent positive-pressure breathing in men

The effect of intermittent positive-pressure breathing (PB), induced by expiring against a resistance of 12.5 mm Hg, on plasma volume and endocrine responses to standing water immersion, was studied in seven male subjects, 28-49 years of age. The men were immersed to the neck (35 +/- 0.5 degrees C) for 90 min with PB from 30 to 60 min. Compared to control values, the hematocrit and hemoglobin concentration decreased (p less than 0.001) during immersion while plasma osmolality was unchanged, indicating an isotonic increase in plasma volume (hemodilution) which peaked after 75 min at +15.5% of the preimmersion plasma volume. This hemodilution was not significantly affected by PB. Plasma renin activity and vasopressin and aldosterone concentrations decreased progressively throughout immersion (p less than 0.001) and were unaffected by PB. The magnitude of these hormonal decreases was accentuated by preexisting, presyncopal symptoms in four subjects. It is concluded that intermittent PB as 12.5 mm Hg failed to compensate for the negative-pressure breathing of standing subjects immersed in water to the neck.     

兔烧伤合并人工海水浸泡后血流动力学变化

建立兔烧伤合并海水浸泡的实验模型 ,观察实验动物血流动力学变化 ,为研究救治烧伤合并海水浸泡伤提供依据     

Exercise participation after menopause

Who should exercise? What exercises should be performed and with what frequency and duration? What benefits can be expected from such exercises? These are some of the questions frequently asked of physicians who care for elderly and post-menopausal patients. Data are conflicting, but significant conclusions can be drawn that will help provide the answers to these questions. This article is written to guide physicians' recommendations to their patients regarding postmenopausal exercise.     

Exercise tolerance and thermoregulatory responses during cycling in boys and men

PURPOSE: Physiological responses to exercise in the heat differ between prepubertal children and young adults. Whether these maturity-related variations imply lower exercise tolerance, inferior thermoregulation, and greater risk for heat injury in the child is uncertain. This study directly compared thermoregulatory and cardiovascular responses as well as endurance performance between prepubertal boys and adult males during steady-load cycling in moderately hot and cool ambient conditions with moderate humidity. METHODS: Eight prepubertal boys (age 11.7 +/- 0.4 yr) and eight adult men (age 31.8 +/- 2.0 yr) performed steady-load cycling to exhaustion at an intensity equivalent to approximately 65% peak V O2 in both hot (approximately 31 degrees C) and cool (approximately 19 degrees C) environments, with fluid intake ad libitum. RESULTS: Exercise duration in the heat was shorter for both groups (hot: men 30.46 +/- 8.84 min, boys 29.30 +/- 6.19 min; cold: men 42.88 +/- 11.79 min, boys 41.38 +/- 6.30 min), with no significant difference between men and boys (P > 0.05). Increases in rectal temperature, heart rate, and cardiac index were similar between groups and conditions. Stroke index, mean arterial pressure, and arterial venous oxygen difference were stable and similar in both conditions, without group differences. No significant dehydration was observed in men or boys. CONCLUSIONS: This study failed to reveal differences in exercise tolerance, thermoregulatory adaptation, or cardiovascular response to exercise in the heat between euhydrated prepubertal boys and adult men.     

Renal, endocrine, and cardiovascular responses during head-out water immersion in legless men.

BACKGROUND: The hydrostatic pressure gradient during head-out water immersion (HOI) causes a blood shift from the legs into the thoracic cavity to stretch the receptors in the cardiac atria and results in a diuresis in hydrated subjects. The present study was conducted to examine whether the HOI-induced diuresis and related circulatory and hormonal changes were attenuated in the subjects who had no legs (legless men). METHODS: Two legless men served as the subjects. They lost both legs 15 and 17 yr ago by accidents and were otherwise healthy. Six normal males participated as controls. The experimental protocol was consisted of a 1-h control, a 3-h HOI (water temperature, 34.5 degrees C) and a 1-h recovery. RESULTS: Average urine flow (0.6 ml x min(-1)), urinary excretion of sodium (90 microeq x min(-1)), and osmolal clearance (1.4 ml x min(-1)) of the legless subjects increased in the first h of immersion to 0.7 ml x min(-1), 139 microeq x min(-1), and 1.8 ml x min(-1), respectively. These values remained elevated during HOI, however, the magnitude of the increase was smaller compared with the control subjects. Plasma arginine vasopressin was significantly (p < 0.05) decreased from 1.0+/-0.4 microU x 100 ml(-1) to 0.4+/-0.2 microU x 100 ml(-1) during HOI in the normal subjects, but was not in the legless subjects (from 0.5 at control period to 0.4 microU x 100 ml(-1) during HOI). A concurrent reduction of aldosterone and plasma renin activity was observed with an increase in atrial natriuretic peptide during HOI in both subject groups, however, the magnitude of the changes was smaller in the legless subjects compared with the control subjects. Similarly, the average increase in cardiac output during HOI in the legless subjects (by 17%) was less compared with the control subjects (by 31%). CONCLUSION: The magnitude of renal, endocrine, and cardiovascular changes in response to HOI in the legless subjects were less than in control subjects, but the responses were qualitatively similar. Accordingly, we suggest that the cephalad blood expansion during immersion is not only due to translocation of blood from the legs but also the abdominal region.     

Long-term, irradiation-induced effects on thermoregulation in the skin after thermal stimulation

PURPOSE: The morphological effect of radiation on the skin has been adequately analyzed, but the functional effect has received little attention. The purpose of this study was to examine the long-term effects of radiation on the skin from the viewpoint of function. MATERIALS AND METHODS: Physiological changes in the irradiated skin of patients who had undergone breast-conserving therapy for the treatment of breast cancer were examined throughout the follow-up period. Thermal stimulation was applied to both breasts, and changes in skin temperature and sweating reactivity of irradiated and non-irradiated skin were measured. RESULTS: From three weeks to the end of radiotherapy, the resting skin temperature of the irradiated region was significantly elevated, while the rate of sweating was lower. More than two years after radiotherapy, the elevated resting skin temperature of the irradiated region had returned to within the range observed for non-irradiated skin, although an abnormally high increase in skin temperature after thermal stimulation continued to be observed for more than two years after radiotherapy. At the same time, sweating after thermal stimulation continued to be suppressed. CONCLUSION: Present observations suggest that functional effects, such as the skin temperature and sweating ability of irradiated skin, persist longer than readily visible morphological changes.     

Exercise training after cardiac transplantation

During the last decade, cardiac transplantation has become the accepted form of treatment for selected patients with end-stage heart disease, which usually results from dilated cardiomyopathy or coronary artery disease. Although 5-yr survival is currently 85%, patients have complicated courses after surgery, with an ever present risk of infection and graft rejection. Because of physical inactivity and severe limitation of cardiac output preoperatively, these deconditioned patients are excellent candidates for medically supervised rehabilitative exercise training programs. Denervation of the myocardium, which occurs with cardiac transplantation, results in a loss of autonomic nervous system modulation of cardiac output, with reliance on circulating catecholamines and with a delayed heart rate and cardiac output response to the onset of exercise. Oxygen uptake kinetics are prolonged, and maximal oxygen uptake is reduced. Additional abnormalities in cardiac and pulmonary artery pressures and in ventilation during exercise have been described. The literature contains seven studies concerning the effects of exercise training in cardiac transplant recipients. Benefits resulting from training include increases in maximal oxygen uptake, peak exercise power output, anaerobic threshold, and lean body mass, reduced perceived exertion, heart rate, and blood pressure during submaximal exercise, and a lowered resting heart rate and blood pressure. There are no data to suggest that exercise training alters the incidence of infection or rejection or improves longevity or return to pre-illness lifestyle.     

Exercise cardiac contractility in men and boys: a recovery echocardiographic study

Previous reports have suggested that children possess limited cardiac functional reserve during exercise compared to young adults. In this study, echocardiography was performed immediately after maximal treadmill exercise to measure left ventricular dimensions and shortening fraction (SF) in college men, and these values were compared to previous results in a post-exercise echocardiographic study of prepubertal boys. Post-exercise SF, change in SF from rest, and percent change in SF from rest were all significantly greater in the post-pubertal subjects. In both men and boys changes in SF following exercise were related to reductions in left ventricular end-systolic dimension, with only minor reductions observed in end-diastolic dimension. These findings support the concept that prepubertal subjects may have inferior myocardial function with exercise when compared to young adults.     

Cardiovascular and metabolic responses at rest and to exercise during 48 hours of head-out immersion: a case report

Head-out immersion in water (HIW) leads to several cardiovascular adjustments. Cardiac output increases by increasing stroke volume with no substantial changes in heart rate (HR) at rest. Therefore, total peripheral resistance to blood flow declines, leading to elevated O₂ delivery. During exercise, cardiac output increases for a given workload while the HR response differs in relation to exercise intensity: it does not change during moderate exercise, but decreases during intense exercise. Oxygen uptake does not change either at rest or during exercise. In this case report, we report data on the cardiovascular and metabolic responses in a 29-year-old man at rest and during constant-load exercise during 48 h of HIW. The subject performed constant-load exercise on cycloergometer at 50% VO_2max in the laboratory and during 48 h of HIW. Pulmonary gas exchange, VO₂ kinetics, HR and rate of perceived exertion were determined. At rest, HR was similar but $\dot VO_2 $ increased during HIW relative to the laboratory. During exercise, the metabolic cost of exercise was similar and HR was the same during HIW and in the laboratory. $\dot VO_2 $ kinetics were faster during HIW. The cardiovascular and metabolic responses at rest and during moderate exercise to a few hours of HIW are not different from those during 48 h of HIW.