[Calf impedance plethysmographic evaluation of peripheral sympathetic nerve activity--comparison with...

Although the method of impedance plethysmography made it possible to evaluate the vascular resistance of lower extremities, the actual correlation to the sympathetic nerve activity is not known. We performed examinations of microneurography and impedance plethysmography of the lower extremities, in six healthy volunteers, placed on a tilting table. Blood pressure, heart rate, muscle nerve sympathetic activity to calf muscles (microneurography), calf vascular resistance (impedance plethysmography) were simultaneously recorded with increasing angles of the head-up tilting (0, 30, 60 degrees). With the increase of tilting angles, sympathetic nerve activity and the calf vascular resistance significantly increased and these values were statistically correlated to the increase of tilting angles (expressed as sine function). Moreover, a statistically significant positive correlation was observed between the sympathetic nerve activity and vascular resistance. We concluded that the impedance plethysmographic method for measurement of calf vascular resistance is a good indicator for evaluating the peripheral sympathetic nerve activity.