Physiological responses to cold exposure in men: a disabled submarine study.

A disabled submarine (DISSUB) lacking power and/or environmental control will become cold, and the ambient air may become hypercapnic and hypoxic. This study examined if the combination of hypoxia, hypercapnia, and cold exposure would adversely affect thermoregulatory responses to acute cold exposure in survivors awaiting rescue. Seven male submariners (33 +/- 6 yrs) completed a series of cold-air tests (CAT) that consisted of 20-min at T(air) = 22 degrees C, followed by a linear decline (1 degrees C x min(-1)) in T(air) to 12 degrees C, which was then held constant for an additional 150-min. CAT were performed under normoxic, normocapnic conditions (D0), acute hypoxia (D1, 16.75% O2), after 4 days of chronic hypoxia, hypercapnia and cold (D5, 16.75% O2, 2.5% CO2, 4 degrees C), and hypoxia-only again (D8, 16.75% O2). The deltaTsk during CAT was larger (P < 0.05) on D0 (-5.2 degrees C), vs. D1 (-4.8 degrees C), D5 (-4.5 degrees C), and D8 (-4.4 degrees C). The change (relative to 0-min) in metabolic heat production (deltaM) at 20-min of CAT was lower (P < 0.05) on D1, D5, and D8, vs. D0, with no differences between D1, D5 and D8. DeltaM was not different among trials at any time point after 20-min. The mean body temperature threshold for the onset of shivering was lower on D1 (35.08 degrees C), D5 (34.85 degrees C), and D8 (34.69 degrees C), compared to D0 (36.01 degrees C). Changes in heat storage did not differ among trials and rectal temperature was not different in D0 vs. D1, D5, and D8. Thus, mild hypoxia (16.75% F1O2) impairs vasoconstrictor and initial shivering responses, but the addition of elevated F1CO2 and cold had no further effect. These thermoregulatory effector changes do not increase the risk for hypothermia in DISSUB survivors who are adequately clothed.

Cold strain index applied to exercising men in cold-wet conditions.

A cold strain index (CSI) based on rectal (T(re)) and mean skin temperatures ((sk)) using data from seminude resting subjects has been proposed (Moran DS, Castellani JW, O'Brien C, Young AJ, and Pandolf KB. Am J Physiol Regulatory Integrative Comp Physiol 277: R556-R564, 1999). The current study determined whether CSI could provide meaningful data for clothed subjects exercising in the cold with compromised insulation. Ten men exercised in cold-wet conditions (CW) for 6 h before (D0) and after 3 days of exhaustive exercise (D3). Each hour of CW consisted of 10 min of standing in rain (5.4 cm/h, 5 degrees C air) followed by 45 min of walking (1.34 m/s, 5.4 m/s wind, 5 degrees C air). The change in T(re) across time was greater (P < 0.05) on D3 than on D0, and the change in (sk) was less (P < 0.05) on D3 than on D0. Although CSI increased across time, the index at the end of both trials (D3 = 4.6 +/- 0.6; D0 = 4.2 +/- 0.8) was similar (P > 0.05). Thus, while (sk) was 1.3 degrees C higher (P < 0.05) and T(re) was 0.3 degrees C lower (P < 0.05) on D3 than on D0, CSI did not discriminate the greater heat loss that occurred on D3. These findings indicate that when vasoconstrictor responses to cold are altered, such as after exhaustive exercise, CSI does not adequately quantify the different physiological strain between treatments. CSI may be useful for indicating increased strain across time, but its utility as a marker of strain between different treatments or studies is uncertain because no independent measure of strain has been used to determine to what extent CSI is a valid and reliable measure of strain.

Thermoregulation during cold exposure after several days of exhaustive exercise.

This study examined the hypothesis that several days of exhaustive exercise would impair thermoregulatory effector responses to cold exposure, leading to an accentuated core temperature reduction compared with exposure of the same individual to cold in a rested condition. Thirteen men (10 experimental and 3 control) performed a cold-wet walk (CW) for up to 6 h (6 rest-work cycles, each 1 h in duration) in 5 degrees C air on three occasions. One cycle of CW consisted of 10 min of standing in the rain (5.4 cm/h) followed by 45 min of walking (1.34 m/s, 5.4 m/s wind). Clothing was water saturated at the start of each walking period (0.75 clo vs. 1.1 clo when dry). The initial CW trial (day 0) was performed (afternoon) with subjects rested before initiation of exercise-cold exposure. During the next 7 days, exhaustive exercise (aerobic, anaerobic, resistive) was performed for 4 h each morning. Two subsequent CW trials were performed on the afternoon of days 3 and 7, approximately 2.5 h after cessation of fatiguing exercise. For controls, no exhaustive exercise was performed on any day. Thermoregulatory responses and body temperature during CW were not different on days 0, 3, and 7 in the controls. In the experimental group, mean skin temperature was higher (P < 0.05) during CW on days 3 and 7 than on day 0. Rectal temperature was lower (P < 0.05) and the change in rectal temperature was greater (P < 0.05) during the 6th h of CW on day 3. Metabolic heat production during CW was similar among trials. Warmer skin temperatures during CW after days 3 and 7 indicate that vasoconstrictor responses to cold, but not shivering responses, are impaired after multiple days of severe physical exertion. These findings suggest that susceptibility to hypothermia is increased by exertional fatigue.