The invention relates to a method for non-invasive determination of oxygen saturationof blood within a deep vascular structure of a human patient comprising locatingon skin of the patient in a vicinity of the deep vascular structure of interestemitter and receiver elements of a light oximeter device, wherein optimal locationof said elements is achieved through matching of a plethysmography trace obtainedfrom the oximeter device to known plethysmography characteristics of the deepvascular structure of interest, and wherein oxygen saturation is determinedfrom a ratio of light absorbed at different wavelengths by haemoglobin in theblood within the vascular structure of interest. The invention also relatesto modified oximetry devices capable of carrying out the method.
