Modulation of arterial baroreflex control of heart rate by skin cooling and heating in humans

The purpose of this study was to examine the effects of skin cooling and he ating on the heart rate (HR) control by the arterial baroreflex in humans. The subjects were 15 healthy men who underwent whole body thermal stress (e sophageal temperatures, similar to 36.8 and similar to 37.0 degrees C; mean skin temperatures, similar to 26.4 and similar to 37.7 degrees C, in skin cooling and heating, respectively) produced by a cool or hot water-perfused suit during supine rest. The overall arterial baroreflex sensitivity in th e RR control was calculated from spontaneous changes in beat-to-beat arteri al pressure and HR during normothermic control and thermal stress periods. The carotid baroreflex sensitivity was evaluated from the maximum slope of the HR response to changes in carotid distending pressure, calculated as me an arterial pressure minus neck pressure. The overall arterial baroreflex s ensitivity at existing arterial pressure increased during cooling(-1.32 +/- 0.25 vs. -2.13 +/- 0.20 beats . min(-1) . mmHg(-1) in the control and cool ing periods, respectively, P < 0.05), whereas it did not change significant ly during heating (-1.39 +/- 0.23 vs. -1.40 +/- 0.15 beats . min(-1) . mmHg (-1) in the control and heating periods, respectively). Neither the cool no r heat loadings altered the carotid baroreflex sensitivity in the HR contro l. These results suggest that the sensitivity of HR control by the extracar otid (presumably aortic) baroreflex was augumented by whole body skin cooli ng, whereas the sensitivities of HR control by arterial baroreflex remain u nchanged during mild whole body heating in humans.