Initial Heat Stress on Subsequent Responses to Cold Water Immersion While Wearing Protective Clothing

SINTEF Technology and Society, Department of Health Research, Trondheim, Norway.
Aviation Space and Environmental Medicine (Impact Factor: 0.88). 08/2012; 83(8):746-50. DOI: 10.3357/ASEM.2844.2012
Source: PubMed


In cold water emergency situations, helicopter aircrew will enter the water with a raised body temperature due to wearing immersion suits. Prewarming has been demonstrated to accelerate core cooling during subsequent cold water immersion (CWI) when wearing swimsuits. For this study we hypothesized that wearing an immersion suit would slow the rate of cooling in subjects who were prewarmed compared to those kept in a normothermic state.
Two different groups of male subjects (age, 24.7 +/- 4.2 yr; height, 183.1 +/- 6.5 cm; weight, 86.7 +/- 15.0 kg; body fat, 16.8 +/- 3.3%) were used to gather data under two conditions: prewarming by exercise (Warm-CWI) and baseline (Base-CWI) when wearing a dry immersion suit (2.97 Clo). In Warm-CWI, seven subjects rested for 20 min and then cycled on an ergometer cycle for 20 min before immersion in water at 5 degrees C for 140 min. In Base-CWI, six subjects were directly immersed in 5 degrees C water after resting.
Tre and Tsk were significantly higher after Warm-CWI at start of CWI, resulting in faster core cooling rate, and a drop in Tre and Tsk during the first 10 min. In the long term, the overall core cooling did not differ between Warm-CWI (0.34 +/- 0.11 degrees C x h(-1)) and Base-CWI (0.31 +/- 0.05 degrees C x h(-1)).
Wearing a dry immersion suit eliminates long-term differences in core cooling between prewarmed subjects and those kept in a normothermic state. When entering cold water with a raised Tre and Tsk, different thermal responses during the first 10 min are expected, but this does not alter long-term core cooling.

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    ABSTRACT: Water covers over 70% of the earth, has varying depths and temperatures and contains much of the earth's resources. Head-out water immersion (HOWI) or submersion at various depths (diving) in water of thermoneutral (TN) temperature elicits profound cardiorespiratory, endocrine, and renal responses. The translocation of blood into the thorax and elevation of plasma volume by autotransfusion of fluid from cells to the vascular compartment lead to increased cardiac stroke volume and output and there is a hyperperfusion of some tissues. Pulmonary artery and capillary hydrostatic pressures increase causing a decline in vital capacity with the potential for pulmonary edema. Atrial stretch and increased arterial pressure cause reflex autonomic responses which result in endocrine changes that return plasma volume and arterial pressure to preimmersion levels. Plasma volume is regulated via a reflex diuresis and natriuresis. Hydrostatic pressure also leads to elastic loading of the chest, increasing work of breathing, energy cost, and thus blood flow to respiratory muscles. Decreases in water temperature in HOWI do not affect the cardiac output compared to TN; however, they influence heart rate and the distribution of muscle and fat blood flow. The reduced muscle blood flow results in a reduced maximal oxygen consumption. The properties of water determine the mechanical load and the physiological responses during exercise in water (e.g. swimming and water based activities). Increased hydrostatic pressure caused by submersion does not affect stroke volume; however, progressive bradycardia decreases cardiac output. During submersion, compressed gas must be breathed which introduces the potential for oxygen toxicity, narcosis due to nitrogen, and tissue and vascular gas bubbles during decompression and after may cause pain in joints and the nervous system. © 2015 American Physiological Society. Compr Physiol 5:1705-1750, 2015.
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