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Introduction: Little is known regarding local differences in foot sweat secretion. Since such information is important to our understanding of sweat gland control for thermoregulatory modeling and for the design of footwear we explored this topic., Methods: Local sweat rates were investigated across core temperatures from 37-39 degrees C, achieved using endogenous (cycling) and exogenous heat (water-perfusion garment: 46 degrees C). Six healthy adults (three men, three women) performed one-legged, incremental cycling in a heated, climate-controlled chamber (36 degrees C, 60% relative humidity). Sweat rates were measured at the forehead and stationary (left) foot (capsules 3.16 cm2): three dorsal sites (base of toes, second metatarsal, and mid point), the lateral, and the central plantar surfaces., Results: Terminal core temperatures ranged between 38.3-39.1 oC, with peak heart rates of 155-187 bpm. Most foot sweat rates were < 50% of that observed at the forehead: dorsal 1 (38%); dorsal 2 (54%); dorsal 3 (37%); lateral (24%); and plantar surfaces (18%). When averaged across the trial, local sweat rates were: 2.61 (forehead); 0.98 (dorsal 1); 1.39 (dorsal 2); 0.95 (dorsal 3); 0.62 (lateral); and 0.47 mg cm2 2 min-1 (plantar)., Conclusion: Two key observations emerged. First, sweat secretion from the experimental foot averaged 30 ml x h(-1), peaking in the last 5 min at 50 ml x h(-1). Second, approximately 70% of the measured sweat flow emanated from the upper skin surfaces, with only 30% coming from the plantar surface.

Background: Motion sickness is a common aeromedical problem that may occur in pilots exposed to increased gravitoinertial load in the head-to-foot direction (+Gz). Since motion sickness may affect autonomic nervous functions including cardiovascular control, it was hypothesized that it might interfere with cardiovascular responses to high +Gz, thereby decreasing G tolerance., Methods: G tolerance and cardiovascular responses to increased G load were studied in nine subjects in a centrifuge environment under two conditions. In the motion sickness condition, the subject was exposed to a motion sickness provocation (MSP) comprising repeated rapid changes in G load in combination with a regimen of head movements. In the control condition the subject was exposed to similar cumulative G-time stress, but without the MSP. Mean arterial pressure (MAP) was measured. An index of peripheral vascular resistance was achieved by measuring the difference in skin temperature between the forearm and fingertip (deltaT(forearm-fingertip))., Results: MSP decreased gradual-onset rate G tolerance from 5.1 +/- 1.0 G (mean +/- SD) to 4.6 +/- 0.9 G. There was no change in gradual-onset rate G tolerance in the control condition. Rapid-onset rate G tolerance was lower in the motion sickness (2.9 +/- 0.5 G) than in the control (3.4 +/- 0.3 G) condition. MSP reduced MAP by 11 mmHg and deltaT(forearm-fingertip) by 4.2 +/- 4.1 degrees C. In the control condition MAP and deltaT(forearm-fingertip) were unaffected., Conclusions: Motion sickness may reduce the arterial pressure response to the extent that the capacity of an individual to withstand increased G loads in the head-to-foot direction is significantly diminished.

Introduction: Selection of preferred skin temperature is a consequence of complex central neural integration of thermoafferent information in the polysynaptic pathway for behavioral thermoregulation. The present study tested the hypothesis that hypoxia alters behavioral temperature regulation., Methods: Eight male volunteers participated in two separate trials. In each trial they were immersed in 28 degrees C water for 90 min, and inspired either room air (air trial) or a hypoxic gas mixture (hypoxia trial; 11.5% O2/88.5% N2). Their left hand was placed in a separate bath perfused with water. At regular intervals they were instructed to adjust the temperature of the water perfusing the hand bath to a comfortable temperature, defined as the 'preferred hand temperature' (Tpref). At minute intervals, esophageal (Tes), rectal (Tre), and skin (Tsk) temperatures, along with heat flux from the skin (Q) and ventilation (VI) were recorded. The observed responses were compared with a one-way ANOVA., Results: With the exception of VI, there were no significant differences in any of the recorded variables between the two conditions. During the immersion, Tes and Tre decreased by 1.0 and 0.7 degrees C, respectively, in the air trial, and by 0.8 and 0.7 degrees C, respectively, in the hypoxia trial. Concomitant with decreases in core temperature, there was a significant increase (p < 0.05) in Tpref of 2.1 degrees C in the air trial and 2.4 degrees C in the hypoxia trial. The difference in Tpref between the air and hypoxia trials was not significant., Discussion: Assuming that the selection of preferred hand temperature represents a behavioral thermoregulatory response, the present results suggest that moderate normobaric hypoxia does not affect human behavioral thermoregulation.