Peripheral vascular resistance increases after termination of obstructive apneas

The mechanisms by which obstructive apneas produce intermittent surges in a rterial pressure remain poorly defined. To determine whether termination of obstructive apneas produce peripheral vasoconstriction, we assessed forear m blood flow during and after obstructive events in sleeping patients exper iencing spontaneous upper airway obstructions. In all subjects, heart rate was monitored with an electrocardiogram and blood pressure was monitored co ntinuously with digital plethysmography. In 10 patients (protocol 1), we us ed forearm plethysmography to assess forearm blood flow, from which we calc ulated forearm vascular resistance by performing venous occlusions during a nd after obstructive episodes. In an additional four subjects, we used simu ltaneous Doppler and B-mode images of the brachial artery to measure blood velocity and arterial diameter, from which we calculated brachial flow cont inuously during spontaneous apneas (protocol 2). In protocol 1, forearm vas cular resistance increased 71% after apnea termination (29.3 +/- 15.4 to 49 .8 +/- 26.5 resistance units, P< 0.05) with all patients showing an increas e in resistance. In protocol 2, brachial resistance increased at apnea term ination in all subjects (219.8 +/- 22.2 to 358.3 +/- 46.1 mmHg . l(-1) . mi n; P = 0.01). We conclude that termination of obstructive apneas is associa ted with peripheral vasoconstriction.