Study objective: To characterize the role of alpha-receptors in autonomic control of digital skin blood flow change in response to obstructive apnea-hypopnea events.
Design: Experimental intervention study.
Setting: Sleep laboratory in a university hospital.
Patients: Eight male patients with severe obstructive sleep apnea (OSA).
Interventions: Patients received four cumulative dosage steps of phentolamine (0.066, 0.2, 2 and 5 [n=3] microg/min/100 ml forearm tissue) via brachial artery infusion during nonrapid eye movement sleep (stage 1 and 2).
Measurements and results: The pulse amplitude determined with peripheral arterial tonometry (PAT) was periodically attenuated during the immediate post apnea-hypopnea period coinciding with arousal. PAT ratio (smallest pulse amplitude post apnea divided by largest pulse amplitude during apnea), was determined as a measure of digital vasoconstriction. We found that, compared with baseline, PAT ratio dose-dependently increased during phentolamine (0.2, 2 and 5 microg) infusion by 11.2+/-1.7%, 24.4+/-2.1% and 30.9+/-4.1%, respectively (P<0.001). Systemic blood pressure and heart rate were largely unaffected by the pharmacological intervention.
Conclusion: OSA related alteration of the pulse amplitude includes a constriction of digital skin vasculature that to a large extent is mediated via sympathoadrenergic alpha-receptors.