Abstract P364: Altered Circadian Rhythm in Blood Pressure in Obstructive Sleep Apnea

Abstract

Background: In people with obstructive sleep apnea (OSA), adverse cardiovascular (CV) events occur most commonly during the night, about 6 hours earlier than the morning peak of events observed in the general population. In healthy individuals, circadian rhythms in many CV risk markers peak in the morning, around the common time of occurrence of adverse CV events. We therefore tested whether circadian rhythms are advanced in those with OSA, which might explain the earlier time of adverse CV events. Methods: Eleven volunteers (4 healthy controls and 7 OSA; 55 ± 5 years of age) completed a 5-day laboratory protocol with sleep and all other behaviors evenly spaced across the 24 h circadian period. To achieve this, after a baseline night, participants completed 10 consecutive short-day cycles of 2 h 40 min each of wakefulness and sleep opportunity. Blood pressure and heart rate were recorded 10 min after each wake time. Salivary melatonin and cortisol concentration were measured at 1-1.5h intervals during wakefulness. Cosinor analyses were performed to determine the rhythmicity of the all variables. We also compared OSA data with larger groups of historical healthy controls from our laboratory. Results: The circadian times of peak systolic and diastolic blood pressure were significantly advanced (up to 7 hours) in OSA as compared to healthy controls, p<0.05. Circadian peaks in all other measured variables were not different between OSA and controls. Conclusions: These results suggest that OSA is associated with a change in the timing of endogenous circadian blood pressure rhythms. This may be specific to the cardiovascular system as there was no evidence for altered phase of melatonin or cortisol secretion patterns. The relatively advanced blood pressure rhythms in OSA is similar to the advancement of the time of adverse CV events in OSA and should be further investigated.