Published ahead of print on January 11, 2007, doi:10.1164/rccm.200609-1271OC
Am. J. Respir. Crit. Care Med., Volume 175, Number 7, April 2007, 720-725
A more recent version of this article appeared on April 1, 2007
Submitted on September 7, 2006
Accepted on January 10, 2007
Effects of CPAP on Cerebral Vascular Response to Hypoxia in Obstructive Sleep Apnea Patients
Glen E Foster1, Patrick J Hanly2, Michele Ostrowski2, and Marc J Poulin3*
1 Department of Physiology and Biophysics, University of Calgary, Calgary, Alberta, Canada,
2 Department of Medicine, University of Calgary, Calgary, Alberta, Canada,
3 Department of Physiology and Biophysics, University of Calgary, Calgary, Alberta, Canada; Department of Clinical Neurosciences, University of Calgary, Calgary, Alberta, Canada; Faculty of Kinesiology, University of Calgary, Calgary, Alberta, Canada
* To whom correspondence should be addressed. 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 twenty minutes of isocapnic hypoxia was measured in eight male patients with OSA before and after 4-6 weeks of continuous positive airway pressure (CPAP) therapy and in ten matched healthy control subjects.
Measurements and Main Results: The cerebral blood flow response to hypoxia was significantly lower in patients with OSA compared to controls (0.56±0.10 vs.0.97±0.09 % change in blood flow velocity per % desaturation, p=0.007, mean ± SE). Following CPAP therapy, the cerebral blood flow response to hypoxia was similar between OSA patients and control (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 apneahypopnea 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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