Changes in blood pressure and plasma norepinephrine during sleep in essential hypertension.

A fall in blood pressure (BP) and the presence of a period of unstable BP during sleep has been reported in humans. However the mechanisms responsible for these phenomena are unclear. In order to examine the role of the sympathetic nervous system in these phenomena, plasma norepinephrine (PNE) was measured in patients with essential hypertension. Blood pressure was monitored under unrestricted conditions by a canula inserted into the brachial artery. During sleep, systolic (SBP) and diastolic blood pressure (DBP) fell by 18.8/13.7 mmHg, respectively. The magnitude of the fall in SBP correlated significantly (p less than 0.05) with the level of PNE in the daytime and with the magnitude of the fall in PNE during sleep. The period of unstable BP and pulse rate was observed during sleep. During this unstable period, BP changed periodically with 20 to 120-second cycles associated with parallel changes in pulse rate. PNE during this period was higher (p less than 0.05) than that during the period of stable BP during sleep. These data suggest that the sympathetic nervous system may play an important role in the fall in BP and unstability of BP during sleep.