Journal of Applied Physiology AJP: Renal Physiology
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J Appl Physiol (August 2, 2007). doi:10.1152/japplphysiol.00115.2007
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Submitted on January 25, 2007
Accepted on July 17, 2007

Baroreflex control of muscle sympathetic nerve activity during skin surface cooling

Jian Cui1, Sylvain Durand2, and Craig G. Crandall3*

1 Institute for Exercise and Environmental Medicine, Presbyterian Hospital of Dallas, Dallas, Texas, United States; Penn State College of Medicine, Penn State Heart & Vascular Institute, Hershey, Pennsylvania, United States
2 Institute for Exercise and Environmental Medicine, Presbyterian Hospital of Dallas, Dallas, Texas, United States
3 Institute for Exercise and Environmental Medicine, Presbyterian Hospital of Dallas, Dallas, Texas, United States; Internal Medicine, University of Texas Southwestern Medical Center at Dallas, 5323 Harry Hines Blvd, dallas, California, United States

* To whom correspondence should be addressed. E-mail: craigcrandall{at}texashealth.org.

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 9 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 °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/mmHg) was not significantly different from normothermic conditions (-2.94 ± 0.21 units/beat/mmHg, 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.






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