Published ahead of print on January 11, 2007, doi:10.1164/rccm.200609-1271OC
© 2007 American Thoracic Society doi: 10.1164/rccm.200609-1271OC
Effects of Continuous Positive Airway Pressure on Cerebral Vascular Response to Hypoxia in Patients with Obstructive Sleep Apnea1 Department of Physiology and Biophysics, 2 Department of Medicine, and 3 Department of Clinical Neurosciences, Faculty of Medicine, and 4 Faculty of Kinesiology, University of Calgary, Calgary, Alberta, Canada Correspondence and requests for reprints should be addressed to Marc J. Poulin, Ph.D., D.Phil., Department of Physiology and Biophysics and Clinical Neurosciences, Faculty of Medicine and Faculty of Kinesiology, University of Calgary, Calgary, AB T2N 4N1, Canada. E-mail: poulin{at}ucalgary.ca Rationale: The mechanism leading to increased risk of stroke in patients with obstructive sleep apnea (OSA) is unknown. It may occur through alteration in the regulation of cerebral blood flow, reflected in part by the response of the cerebral vasculature to hypoxia. We hypothesized that the cerebrovascular response to hypoxia is reduced in patients with OSA. Objective: To determine the cerebral blood flow response to hypoxia in patients with OSA. Methods: The cerebral blood flow response to 20 minutes of isocapnic hypoxia was measured in eight male patients with OSA before and after 4 to 6 weeks of continuous positive airway pressure (CPAP) therapy and in 10 matched healthy control subjects. Measurements and Main Results: The cerebral blood flow response to hypoxia was significantly lower in patients with OSA compared with control subjects (0.56 ± 0.10 vs. 0.97 ± 0.09% [mean ± SE] change in blood flow velocity per % desaturation; p = 0.007). After CPAP therapy, the cerebral blood flow response to hypoxia was similar between patients with OSA and control subjects (1.08 ± 0.15 vs. 0.92 ± 0.13% change in blood flow velocity per % desaturation; p = 0.4). Moderately strong correlations were found between the cerebral blood flow response to hypoxia and the apnea–hypopnea index (r = –0.57; p = 0.04) and nocturnal oxyhemoglobin saturation (r = 0.48; p = 0.01). Conclusions: The cerebral blood flow response to hypoxia is significantly reduced in patients with OSA. Treatment of OSA with CPAP increases the cerebral blood flow response to hypoxia to normal levels. An attenuated cerebrovascular response to hypoxia in patients with OSA may contribute to their elevated risk of stroke.
Key Words: patients • cerebrovascular disorders • cardiovascular physiologic processes
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