Effects of emotional and mental stress on muscle sympathetic nerve activity in humans

Abstract

Mental stress consistently increases arterial blood pressure and heart rate, but sympathetic neural responses remain controversial. The purpose of this study was to investigate cardiovascular and neural responses to viewing negative pictures, and compare those responses to a standard mental stress protocol. Muscle sympathetic nerve activity (MSNA), mean arterial pressure (MAP), heart rate (HR), and perceived stress levels were recorded in 12 healthy men in the prone position during three trials: 1) neutral pictures, 2) negative pictures, and 3) mental arithmetic. MAP and HR increased during mental arithmetic (Δ13±3 mmHg and A13±2 beats/min; P<0.001), but did not change during negative or neutral pictures. MSNA did not change during neutral pictures (Δ2±l bursts/min; n=11), negative pictures (Δ0±l bursts/min; n=11), or mental arithmetic (Δ0±l bursts/min; n=8). MSNA increased during recovery from mental arithmetic (Δ4±2 bursts/min; P<0.05), but did not change during recovery from negative or neutral pictures. Perceived stress levels increased more dramatically during mental arithmetic (3±0 a.u.) compared to negative pictures (2±0 a.u.; P<0.001). These findings demonstrate that emotional stress evoked by negative pictures does not alter cardiovascular and muscle sympathetic neural activity in humans, and challenges the concept that the perception of stress modulates MSNA responses to mental stress in humans.