Abstract: A computer-implemented method for assessing peripheral arterial tone (100), PAT, of an individual (1) monitored by optical plethysmography and for detecting therefrom occurrence of a sleep-related event, comprising:—obtaining: o an optical plethysmography signal (101) measured at an investigated volume (11); and o light intensities (102;103) acquired at two or more points in time (12;13) along said optical plethysmography signal (101);—determining changes in arterial blood volume (16) in said investigated volume (11) between said two or more points in time (12;13) by determining a logarithm (17) or a function approximation thereof (17) of a function of said light intensities (102;103), thereby assessing PAT (100) of said individual (1); and—determining a drop in said PAT (100) indicative for a vasoconstriction of arteries and arterioles in said investigated volume (11), thereby detecting occurrence of a sleep-related event.