Neurovascular responses to mental stress in the supine and upright postures

Abstract

The purpose of this study was to determine neurovascular responses to mental stress (MS) in the supine and upright postures. MS was elicited in 23 subjects (26 +/- 1 yr) by 5 min of mental arithmetic. In study 1 (n = 9), Doppler ultrasound was used to measure mean blood flow velocity in the renal (RBFV) and superior mesenteric arteries (SMBFV), and venous occlusion plethysmography was used to measure forearm blood flow (FBF). In study 2 (n = 14), leg blood flow (LBF; n = 9) was measured by Doppler ultrasound, and muscle sympathetic nerve activity (MSNA; n = 5) was measured by microneurography. At rest, upright posture increased heart rate and MSNA and decreased LBF, FBF, RBFV, and SMBFV and their respective conductances. MS elicited similar increases in mean arterial blood pressure ( approximately 12 mmHg) and heart rate ( approximately 17 beats/min), regardless of posture. MS in both postures elicited a decrease in RBFV, SMBFV, and their conductances and an increase in LBF, FBF, and their conductances. Changes in blood flow were blunted in the upright posture in all vascular beds examined, but the pattern of the vascular response was the same as the supine posture. MS did not change MSNA in either posture (change: approximately 1 +/- 3 and approximately 3 +/- 3 bursts/min, respectively). In conclusion, the augmented sympathetic activity of the upright posture does not alter heart rate, mean arterial blood pressure, or MSNA responses to MS. MS elicits divergent vascular responses in the visceral and peripheral vasculature. These results indicate that, although the upright posture attenuates vascular responses to MS, the pattern of neurovascular responses does not differ between postures.

Figure 1

Comparable increases in mean arterial pressure (MAP) and heart rate (HR) during mental stress in the supine and upright postures while measuring blood flow velocity in either the renal or superior mesenteric artery. B, baseline, R, recovery.

Figure 2

Vascular conductance decreased from baseline during mental stress in the renal and superior mesenteric arteries in both postures. A significant interaction was recorded when absolute values were compared for both postures in both arteries. However, when changes in conductance were expressed as a percent change from baseline, vascular responses to mental stress did not differ between postures. B, baseline, R, recovery.

Figure 3

Forearm blood flow (FBF) and vascular conductance (FVC) increased from baseline during mental stress in both postures in the renal trials. Greater increases in FBF and FVC were observed in the supine compared to the upright postures. Percent change from baseline in FBF and FVC were not significantly different during mental stress in the supine and upright postures. B, baseline, R, recovery.

Figure 4

Mental stress increased mean arterial pressure (MAP) and heart rate (HR) in both postures (n = 9). Leg blood flow (LBF) and vascular conductance (LVC) increased from baseline during mental stress in both postures. Greater increases in LVC were observed in the supine compared to the upright postures. Percent change from baseline in LBF and LVC were not significantly different during mental stress in the supine and upright postures. B, baseline, R, recovery.

Figure 5

During muscle sympathetic nerve activity (MSNA) trials mental stress increased mean arterial pressure (MAP) and heart rate (HR) in both postures (n = 5). Changes in MSNA burst frequency and total activity did not differ between the two postures. B, baseline, R, recovery.