Does The Reactivity Of The Sympathetic Nervous System Contribute To The Morning Surge In Blood Pressure?

Abstract

We determined whether the reactivity of the sympathetic nervous system (SNS) is related to the morning surge in blood pressure. Ambulatory blood pressure recordings were obtained from 33 subjects (14 males / 19 females ) and the amplitude, the rate of rise (RoR) and the rate x amplitude product (BPPower) of morning mean arterial pressure (MAP) were determined mathematically. Subjects were average age 41 + 4 years (range 18 ‐ 83), BMI 26+1 and 24% of whom were taking antihypertensive therapy. The reactivity of the SNS to an aversive stimulus was assessed on a separate day by microneurographic recording of multiunit, postganglionic muscle sympathetic nerve activity (MSNA), measured from the peroneal nerve. MAP and MSNA were measured concurrently at rest and during a cold pressor test (hand in ice water for 2 min). The cold pressor test increased MSNA and MAP by 24.0 + 2.4 mmHg. MSNA was adjusted for age and BMI. BPPower and RoR were positively correlated to the cold pressor induced increase in total MSNA (r=0.4, P=0.02) and MSN burst amplitude (r=0.5, P=0.01) but were not related to the increase in MSNA frequency. These results suggest that the CNS mechanisms influencing the increase in MSN burst amplitude during arousal may also be fundamental in determining the rate of blood pressure rise during the morning period.Supported by NHMRC project grant 317826