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This Article Full Text Full Text (PDF) All Versions of this Article: 92/2/391    most recent expphysiol.2006.035584v1 Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Cooper, V. L. Articles by Hainsworth, R. Search for Related Content PubMed PubMed Citation Articles by Cooper, V. L. Articles by Hainsworth, R.

¹ Institute for Cardiovascular Research, University of Leeds, Leeds LS2 9JT, UK ² Department of Respiratory Medicine, Leeds Teaching Hospitals NHS Trust, Leeds LS1 3EX, UK ³ Department of Physiology, Medical School, Jordan University of Science and Technology, Irbid, Jordan

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 h between 09.00 and 21.00 h 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 maximal slopes and the corresponding carotid sinus pressures, respectively. We found that at 09.00 h, sensitivity for the control of vascular resistance was at its lowest (–1.2 ± 0.2% mmHg^–1, compared with –1.9 ± 0.3% mmHg^–1 at 12.00 h, P < 0.02) and operating point for control of mean arterial pressure was at its highest (101.1 ± 5.8 mmHg, compared with 94.1 ± 5.8 mmHg at 12.00 h, 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 h. 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.

(Received 25 August 2006; accepted after revision 2 January 2007; first published online 4 January 2007)
Corresponding author V. L. Cooper: Institute for Cardiovascular Research, University of Leeds, Leeds LS2 9JT, UK. Email: victoria.cooper{at}leedsth.nhs.uk