O'Brien C, Young A J, Sawka M N
United States Army Research Institute of Environmental Medicine, Natick, Massachusetts 01760, USA.
J Appl Physiol (1985). 1998 Jan;84(1):185-9. doi: 10.1152/jappl.1998.84.1.185.
This study examined the effects of hypohydration on thermoregulation during cold exposure. In addition, the independent influences of hypohydration-associated hypertonicity and hypovolemia were investigated. Nine male volunteers were monitored for 30 min at 25 degrees C, then for 120 min at 7 degrees C, under three counterbalanced conditions: euhydration (Eu), hypertonic hypohydration (HH), and isotonic hypohydration (IH). Hypohydration was achieved 12 h before cold exposure by inducing sweating (HH) or by ingestion of furosemide (IH). Body weight decrease (4.1 +/- 0.2%) caused by hypohydration was similar for HH and IH, but differences (P < 0.05) were found between HH and IH in plasma osmolality (292 +/- 1 vs. 284 +/- 1 mosmol/kgH2O) and plasma volume reduction (-8 +/- 2 vs. -18 +/- 3%). Heat debt (349 +/- 14 among) did not differ (P > 0.05) among trials. Mean skin temperature decreased throughout cold exposure during Eu but plateaued after 90 min during HH and IH. Forearm-finger temperature gradient tended (P = 0.06) to be greater during Eu (10.0 +/- 0.7 degrees C) than during HH or IH (8.9 +/- 0.7 degrees C). This suggests weaker vasoconstrictor tone during hypohydration than during Eu. Final mean skin temperature was higher for HH than for Eu or IH (23.5 +/- 0.3, 22.6 +/- 0.4, and 22.9 +/- 0.3 degrees C, respectively), and insulation was lower on HH than on IH (0.13 +/- 0.01 vs. 0.15 +/- 0.01 degree C.W-1.m-2, respectively), but not with Eu (0.14 +/- 0.01 degree C.W-1.m-2). This provides some evidence that hypertonicity impairs the vasoconstrictor response to cold. Although mild hypohydration did not affect body heat balance during 2-h whole body exposure to moderate cold, hypohydration-associated hypertonicity may have subtle effects on vasoconstriction that could become important during a more severe cold exposure.
本研究考察了低水合状态对冷暴露期间体温调节的影响。此外，还研究了与低水合相关的高渗状态和血容量减少的独立影响。9名男性志愿者在三种平衡条件下接受监测：正常水合状态（Eu）、高渗性低水合状态（HH）和等渗性低水合状态（IH）。在25℃下监测30分钟，然后在7℃下监测120分钟。低水合状态在冷暴露前12小时通过诱导出汗（HH）或摄入速尿（IH）来实现。HH组和IH组因低水合导致的体重下降（4.1±0.2%）相似，但HH组和IH组在血浆渗透压（292±1与284±1毫摩尔/千克H₂O）和血浆量减少（-8±2与-18±3%）方面存在差异（P<0.05）。各试验间热债（349±14）无差异（P>0.05）。在Eu组冷暴露期间平均皮肤温度持续下降，但在HH组和IH组90分钟后趋于平稳。前臂-手指温度梯度在Eu组（10.0±0.7℃）往往（P=0.06）比HH组或IH组（8.9±0.7℃）更大。这表明低水合状态下血管收缩张力比Eu组弱。HH组最终平均皮肤温度高于Eu组或IH组（分别为23.5±0.3、22.6±0.4和22.9±0.3℃），HH组的隔热性低于IH组（分别为0.13±0.01与0.15±0.01℃·W⁻¹·m⁻²），但与Eu组无差异（0.14±0.01℃·W⁻¹·m⁻²）。这提供了一些证据表明高渗状态会损害对寒冷的血管收缩反应。尽管轻度低水合在2小时全身中度冷暴露期间不影响身体热平衡，但与低水合相关的高渗状态可能对血管收缩有细微影响，在更严重的冷暴露期间可能变得重要。
