Sleep and blood pressure: spontaneous baroreflex sensitivity in dippers and non-dippers

Baroreflex sensitivity (BRS) increases during sleep, whereas arterial blood pressure falls. Some hypertensive patients do not have a nocturnal fall in blood pressure (non-dippers). The objective was to ascertain whether there is a difference between 24 h BRS values in dippers and non-dippers that might account for the difference in nocturnal blood pressure behaviour.

In a group of consecutive untreated hypertensive patients undergoing 24 h ambulatory intra-arterial blood pressure (IABP) monitoring, 18 were non-dippers i.e., their mean IABP during sleep failed to drop by 10% of their waking IABP. Each non-dipper was matched for age and waking IABP with two dippers. The BRS had previously been assessed with the "Oxford' bolus phenylephrine technique; spontaneous BRS was assessed throughout the 24 h period by off-line computer analysis of spontaneous variations in IABP and R-R interval.

In both groups there was a significant increase in spontaneous BRS during sleep (P < 0.0001 for dippers, P < 0.0001 for non-dippers). There was no significant difference between spontaneous BRS in dippers and non-dippers, when they were either awake or asleep.

BRS did not differ significantly between dippers and non-dippers, when they were either awake or asleep. Changes in BRS during sleep are not likely to account for the abnormal dipping pattern in a minority of hypertensives and are not likely to contribute to the normally observed nocturnal fall in blood pressure.