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

TLDR

The study aimed to assess how the cold pressor test influences sympathetic nerve activity and its correlation with arterial pressure, heart rate, and plasma norepinephrine in conscious humans. Twenty‑five healthy volunteers had arterial pressure, heart rate, and peroneal muscle sympathetic nerve activity recorded while their hand was immersed in ice water for two minutes. During the test, arterial pressure rose steadily, muscle sympathetic activity increased markedly after 30 s (to 386 units by minute 1 and 574 units by minute 2), while heart rate spiked in the first 30 s and then returned to baseline; beta‑adrenergic blockade eliminated the heart‑rate rise, and sympathetic activity correlated strongly with mean arterial pressure and venous norepinephrine but only weakly with plasma norepinephrine. The abstract was truncated at 250 words.

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 X amplitude) did not increase in the first 30 seconds of the test but increased from 230 +/- 27 to 386 +/- 52 units (mean +/- SE, p less than 0.05) by the end of the first minute of the test and to 574 +/- 73 (p less than 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 beta-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 less than 0.01) and peripheral venous norepinephrine (r = 0.72, p less than 0.05); however, large changes in nerve traffic were associated with small changes in plasma norepinephrine. (ABSTRACT TRUNCATED AT 250 WORDS)