Cui Jian, Durand Sylvain, Crandall Craig G
Institute for Exercise and Environmental Medicine, Presbyterian Hospital of Dallas, 7232 Greenville Ave., Dallas, TX 75231, USA.
J Appl Physiol (1985). 2007 Oct;103(4):1284-9. doi: 10.1152/japplphysiol.00115.2007. Epub 2007 Aug 2.
Skin surface cooling improves orthostatic tolerance through a yet to be identified mechanism. One possibility is that skin surface cooling increases the gain of baroreflex control of efferent responses contributing to the maintenance of blood pressure. To test this hypothesis, muscle sympathetic nerve activity (MSNA), arterial blood pressure, and heart rate were recorded in nine healthy subjects during both normothermic and skin surface cooling conditions, while baroreflex control of MSNA and heart rate were assessed during rapid pharmacologically induced changes in arterial blood pressure. Skin surface cooling decreased mean skin temperature (34.9 +/- 0.2 to 29.8 +/- 0.6 degrees C; P < 0.001) and increased mean arterial blood pressure (85 +/- 2 to 93 +/- 3 mmHg; P < 0.001) without changing MSNA (P = 0.47) or heart rate (P = 0.21). The slope of the relationship between MSNA and diastolic blood pressure during skin surface cooling (-3.54 +/- 0.29 units.beat(-1).mmHg(-1)) was not significantly different from normothermic conditions (-2.94 +/- 0.21 units.beat(-1).mmHg(-1); P = 0.19). The slope depicting baroreflex control of heart rate was also not altered by skin surface cooling. However, skin surface cooling shifted the "operating point" of both baroreflex curves to high arterial blood pressures (i.e., rightward shift). Resetting baroreflex curves to higher pressure might contribute to the elevations in orthostatic tolerance associated with skin surface cooling.
皮肤表面冷却通过一种尚未明确的机制提高直立耐受能力。一种可能性是，皮肤表面冷却增加了压力反射对传出反应的控制增益，有助于维持血压。为了验证这一假设，在正常体温和皮肤表面冷却条件下，记录了9名健康受试者的肌肉交感神经活动（MSNA）、动脉血压和心率，同时在药理学诱导的动脉血压快速变化期间评估了MSNA和心率的压力反射控制。皮肤表面冷却降低了平均皮肤温度（从34.9±0.2℃降至29.8±0.6℃；P<0.001），并增加了平均动脉血压（从85±2 mmHg升至93±3 mmHg；P<0.001），而MSNA（P = 0.47）或心率（P = 0.21）没有变化。皮肤表面冷却期间MSNA与舒张压之间关系的斜率（-3.54±0.29单位·次-1·mmHg-1）与正常体温条件下（-2.94±0.21单位·次-1·mmHg-1；P = 0.19）无显著差异。描述心率压力反射控制的斜率也未因皮肤表面冷却而改变。然而，皮肤表面冷却将两条压力反射曲线的“工作点”都转移到了较高的动脉血压水平（即向右移位）。将压力反射曲线重置为更高的压力可能有助于提高与皮肤表面冷却相关的直立耐受能力。
