Received August 25, 2006
Revised November 30, 2006
Accepted after revision January 2, 2007

¹ University of Leeds
² Leeds Teaching Hospitals NHS Trust
³ Jordan University of Science and Technology

^* To whom correspondence should be addressed. E-mail: vic.c{at}tiscali.co.uk.

	Abstract

Obstructive events during sleep in patients with obstructive sleep apnoea (OSA) cause large alterations in blood pressure and this may lead to changes in baroreflex function with implications for long term blood pressure control. This study examined the daytime variations in the responses to carotid baroreceptor stimulation in OSA patients. We determined the cardiac and vascular responses every 3 hours between 09:00 and 21:00 in 20 patients with OSA, using graded suctions and pressures applied to a neck collar. These responses were plotted against estimated carotid sinus pressures and, from these plots, baroreflex sensitivities and "operating points" were taken as the maximum slopes and the corresponding carotid sinus pressures, respectively. We found that at 09:00, sensitivity for the control of vascular resistance was at its lowest (-1.2±0.2%.mmHg^-1, compared to -1.9±0.3%.mmHg^-1 at 12:00, P<0.02) and "operating point" for control of mean arterial pressure was at its highest (101.1±5.8 mmHg compared to 94.1± 5.8mmHg to at 12:00, P<0.05). This is in contrast to previous data from normal subjects in whom sensitivity was highest and "operating point" lowest at 09:00. We suggest that the higher baroreflex sensitivity and lower "operating point" seen in the mornings in normal subjects may provide a protective mechanism against hypertension and that this protection is absent in patients with OSA. It is possible that the reduced reflex sensitivity and increased "operating point" in the mornings may actually promote hypertension.

Key Words: Apnoea, Arterial baroreflex, Hypertension