We investigated a non-invasive measurement for changes in finger blood flow during wakefulness and sleep. Changes in finger blood flow, reflected by pulse wave amplitude (PWA) derived from finger plethysmography, were compared with changes in forearm vascular flow assessed by venous occlusion plethysmography after intra-arterial infusion of norepinephrine (NE), phentolamine, and isoproterenol (n=15, 15, 14 subjects, respectively). Moreover, PWA was assessed during obstructive breathing during sleep (n=8 patients). Vasoconstriction in the finger (PWA) was stronger than that obtained in the forearm vascular bed in the higher NE dose range both without (ANOVA, P=0.002) and with concomitant phentolamine-induced alpha-receptor blockade (P=0.02). Isoproterenol increased forearm blood flow but did not induce flow changes detectable by the finger plethysmographic technique (P<0.001). PWA was significantly reduced during arousal from obstructive sleep apnea (-37.5+/-16.1%, P=0.002, n=6 patients), suggesting vasoconstriction in the digital vascular bed. PWA derived from finger plethysmography allows continuous, non-invasive measurement of changes in finger blood flow during wakefulness and sleep. However, as may be expected from the anatomical and functional differences between the finger and forearm vascular beds and demonstrated by the lack of response to beta(2)-receptor stimulation, PWA does not mimic forearm vascular flow characteristics. Thus, finger plethysmography may be a useful complement to current vascular research techniques, in particular to monitor sympathetic influences on skin blood flow in the finger.