Muscle Sympathetic Nerve Activity and Cerebrovascular Responses to Mental Stress.

Mental stress has been shown to elicit increases in arterial blood pressure, heart rate and cerebral blood flow, whereas the degree of sympathoexcitation induced by mental stress has been shown to be inconsistent. Previous studies have examined the relationship between limb vascular responsiveness and muscle sympathetic nerve activity (MSNA) during mental stress; however, this has not been studied in relation to the cerebral vasculature. The purpose of this study was to examine concurrent neural and cerebrovascular responses to mental stress. Thirteen healthy adults (men/women: 7/6; age = 28 ± 5 years; BMI = 25 ± 2 kg/m ) completed the Stroop Color Word Test. Beat-to-beat mean arterial pressure (MAP) using finger photoplethysmograpy, heart rate (HR) using a 3-lead ECG, middle cerebral artery velocity (MCAv) using transcranial doppler ultrasound, and MSNA using microneurography were continuously recorded at baseline and in response to the Stroop Color Word Test. The response to the mental stress was recorded as the change from baseline. Linear regression was used to assess the influence of MSNA on cerebrovascular and hemodynamic variables. As expected, there were increases in HR (baseline = 58 ± 8 bpm vs. Stroop = 66 ± 10 bpm; p = 0.045) and MCAv (baseline = 58 ± 8 cm/s vs. Stroop = 69 ± 13 cm/s; p = 0.016) from baseline during the Stroop test. However, there was no change in MAP (baseline = 96 ± 16 mmHg vs. Stroop = 99 ± 17 mmHg; p > 0.05) or MSNA (baseline = 16 ± 6 bursts/min vs. Stroop = 17 ± 7 bursts/min; p > 0.05) from baseline during the Stroop test. Although the change in MAP was positively associated with the change in MCAv (r = 0.46, p = 0.025), there were no associations between the change in MSNA and the increase in MCAv, MAP, or HR in response to the Stroop test. In conclusion, our results demonstrate a disassociation between the MSNA, MAP and MCAv responses to mental stress. It is also possible that the temporal response to mental stress is different and future studies could examine the time course of the sympathetic and cerebrovascular responses.