Baroreflex control of muscle sympathetic nerve activity during skin surface cooling.
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.
Institute for Exercise and Environmental Medicine, Presbyterian Hospital of Dallas, 7232 Greenville Ave., Dallas, TX 75231, USA.
Jian
J
Cui
Sylvain
S
Durand
Craig G
CG
Crandall
D000328:Adult; D017704:Baroreflex / Q000502:physiology*; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology; D001833:Body Temperature Regulation / Q000502:physiology*; D004359:Drug Therapy, Combination; D005260:Female; D006339:Heart Rate; D006801:Humans; D008297:Male; D009055:Mouth; D018482:Muscle, Skeletal / Q000294:innervation*; D009599:Nitroprusside; D010656:Phenylephrine; D012867:Skin / Q000098:blood supply*; D012881:Skin Temperature / Q000502:physiology*; D013564:Sympathetic Nervous System / Q000502:physiology*; D014662:Vasoconstrictor Agents; D014665:Vasodilator Agents
D014662:Vasoconstrictor Agents; D014665:Vasodilator Agents; D009599:Nitroprusside; D010656:Phenylephrine