Effects of the cold pressor test on muscle sympathetic nerve activity in humans

Abstract

The purpose of this study was to determine the effects of the cold pressor test on sympathetic outflow with direct measurements of nerve traffic in conscious humans and to test the strength of correlation between sympathetic nerve discharge and the changes in arterial pressure, heart rate, and plasma norepinephrine. In 25 healthy subjects, arterial pressure, heart rate, and muscle sympathetic nerve activity were measured with microelectrodes inserted percutaneously into a peroneal muscle nerve fascicle in the leg during immersion of the hand in ice water for 2 minutes. Arterial pressure rose steadily during the first and second minutes of the cold pressor test. Muscle sympathetic activity (burst frequency × amplitude) did not increase in the first 30 seconds of the test but increased from 230 ± 27 to 386 ± 52 units (mean ± SE, p < 0.05) by the end of the first minute of the test and to 574 ±73 (p < 0.01) during the second minute. In contrast, heart rate increased maximally during the first 30 seconds of the cold pressor test and returned to control during the second minute. The increases in heart rate were abolished by β-adrenergic blockade. The increases in muscle sympathetic activity during the cold pressor test were correlated with the increases in both mean arterial pressure (r = 0.86, p < 0.01) and peripheral venous norepinephrine (r = 0.72, p < 0.05); however, large changes in nerve traffic were associated with small changes in plasma norepinephrine. The major new conclusions from this study are that 1) stimulation of sympathetic neural outflow to skeletal muscle is an important component of the sympathetic response to the cold pressor test, 2) the cold pressor test appears to produce differentia] effects on sympathetic outflow to the heart and to the skeletal muscles, and 3) the arterial pressure response to the cold pressor test provides an approximate index of muscle sympathetic activity in this setting.© 1987 American Heart Association, Inc.