Association between cognitive dysfunction and nocturnal peaks of blood pressure estimated from pulse transit time in obstructive sleep apnoea

Background: Obstructive sleep apnoea (OSA) is characterised by recurrent episodes of partial or complete cessation of breathing during sleep and an increased effort to breathe. Patients with untreated OSA exhibit cognitive impairment that is only partly accounted for by hypoxia and sleep disruption, suggesting that other factors remain to be identified. OSA can involve repeated spikes of nocturnal blood pressure because of increased activity of the sympathetic nervous system during sleep. While high resting blood pressure is associated with cognitive dysfunction, it is not yet known whether peaks in nocturnal blood pressure are associated with cognitive impairment in OSA. Methods: A cohort of patients participated in overnight polysomnographic studies at a major sleep laboratory to investigate whether nocturnal elevations in blood pressure are associated with cognitive dysfunction in OSA. Nocturnal pulse transit time was measured as a surrogate for arterial blood pressure during sleep. Results: Of the 75 patients, 12 had no obstructive sleep apnoea, 26 had mild OSA, 18 moderate, and 19 severe OSA. The results revealed that systolic blood pressure peaks were associated with OSA severity, while diastolic blood pressure peaks were not. Peaks of nocturnal systolic blood pressure were independently associated with poorer performance on a test of visuospatial function, but not with impairments on tests of sustained attention, reaction time or autobiographical memory. Conclusion: The present findings indicate nocturnal peaks of systolic blood pressure that are substantially higher than normal daytime values may contribute to visuospatial dysfunction in OSA.