Sympathetic neural responses to mental stress: responders, nonresponders and sex differences

Abstract

Mental stress consistently increases heart rate (HR) and blood pressure (BP) in humans, despite inconsistent sympathetic neural responses that include increases, decreases, or no change in muscle sympathetic nerve activity (MSNA). The purpose of the present study was to examine associations between MSNA, BP, and HR responses to mental stress. Leg MSNA, BP, HR, and perceived stress levels were recorded during 3–5 min of mental arithmetic in 82 subjects (53 men and 29 women). Subjects were divided into positive responders (≥Δ3 bursts/min; n = 40), negative responders (≤Δ−3 bursts/min; n = 9), and nonresponders ( n = 33). Mental stress increased MSNA in positive responders (Δ6 ± 1 bursts/min), decreased MSNA in negative responders (Δ−6 ± 1 bursts/min), and did not change MSNA in nonresponders (Δ1 ± 1 bursts/min). Mental stress increased mean BP and HR similarly in positive responders (Δ15 ± 1 mmHg and Δ16 ± 1 beats/min; P < 0.001), nonresponders (Δ15 ± 1 mmHg and Δ19 ± 2 beats/min; P < 0.001), and negative responders (Δ12 ± 2 mmHg and Δ19 ± 3 beats/min; P < 0.001). Perceived stress levels and sex distributions were similar across responders and nonresponders; thus, perceived stress and sex do not appear to influence MSNA during mental stress. However, men demonstrated higher increases of mean BP during mental stress when compared with women (Δ16 ± 1 vs. Δ12 ± 1 mmHg; P < 0.05), despite no differences in MSNA responses. In conclusion, our results demonstrate marked differences in MSNA responses to mental stress and a disassociation between MSNA and BP responses to mental stress, suggesting complex patterns of vascular responsiveness during mental stress.