Impaired vascular regulation in patients with obstructive sleep apnea: effects of continuous positive airway pressure treatment.
BACKGROUND
Impaired endothelium-dependent vasodilation has been documented in patients with sleep apnea. This impairment may result in blood flow dysregulation during apnea-induced fluctuations in arterial blood gases.


OBJECTIVE
To test the hypothesis that hypoxic and hypercapnic vasodilation in the forearm and cerebral circulation are impaired in patients with sleep apnea.


METHODS
We exposed 20 patients with moderate to severe sleep apnea and 20 control subjects, to isocapnic hypoxia and hyperoxic hypercapnia. A subset of 14 patients was restudied after treatment with continuous positive airway pressure.


RESULTS
Cerebral flow velocity (transcranial Doppler), forearm blood flow (venous occlusion plethysmography), arterial pressure (automated sphygmomanometry), oxygen saturation (pulse oximetry), ventilation (pneumotachograph), and end-tidal oxygen and carbon dioxide tensions (expired gas analysis) were measured during three levels of hypoxia and two levels of hypercapnia. Cerebral vasodilator responses to hypoxia (-0.65 +/- 0.44 vs. -1.02 +/- 0.72 [mean +/- SD] units/% saturation; P = 0.03) and hypercapnia (2.01 +/- 0.88 vs. 2.57 +/- 0.89 units/mm Hg; P = 0.03) were smaller in patients versus control subjects. Hypoxic vasodilation in the forearm was also attenuated (-0.05 +/- 0.09 vs. -0.10 +/- 0.09 unit/% saturation; P = 0.04). Hypercapnia did not elicit forearm vasodilation in either group. Twelve weeks of continuous positive airway pressure treatment enhanced hypoxic vasodilation in the cerebral circulation (-0.83 +/- 0.32 vs. -0.46 +/- 0.29 units/% saturation; P = 0.01) and forearm (-0.19 +/- 0.15 vs. -0.02 +/- 0.08 units/% saturation; P = 0.003), and hypercapnic vasodilation in the brain showed a trend toward improvement (2.24 +/- 0.78 vs. 1.76 +/- 0.64 units/mm Hg; P = 0.06).


CONCLUSIONS
Vasodilator responses to chemical stimuli in the cerebral circulation and the forearm are impaired in many patients with obstructive sleep apnea. Some of these impairments can be improved with continuous positive airway pressure.
Reichmuth
Kevin J
KJ
Departments of Medicine, School of Medicine and Public Health, University of Wisconsin-Madison and Middleton Veterans Administration Hospital, Madison, WI, USA.
Dopp
John M
JM
Barczi
Steven R
SR
Skatrud
James B
JB
Wojdyla
Piotr
P
Hayes
Don
D
Morgan
Barbara J
BJ
D000328:Adult; D001783:Blood Flow Velocity; D001794:Blood Pressure; D002560:Cerebrovascular Circulation; D045422:Continuous Positive Airway Pressure / Q000379:methods*; D005260:Female; D005500:Follow-Up Studies; D005542:Forearm / Q000098:blood supply; D006801:Humans; D006935:Hypercapnia / Q000503:physiopathology; D000860:Hypoxia / Q000503:physiopathology; D008297:Male; D010092:Oximetry; D010100:Oxygen / Q000378:metabolism; D010991:Plethysmography / Q000379:methods; D012891:Sleep Apnea Syndromes / Q000503:physiopathology; D020181:Sleep Apnea, Obstructive / Q000503:physiopathology* / Q000628:therapy*; D017585:Ultrasonography, Doppler, Transcranial / Q000379:methods; D014664:Vasodilation
D010100:Oxygen