The present invention relates to a therapy system comprising: a patient interface (16) for delivering a flow of breathable gas to a patient (10), wherein the patient interface (16) comprises a detection unit (24) for detecting reflected light from a skin area (22) of the patient (10) and generating an image signal from the detected light； a processing unit (26) for processing the image signal； and an evaluation unit (28) for deriving information on a vital state of the patient (10) based on an evaluation of a development of the image signal over time； wherein the processing unit (26) is configured to identify a blood vessel of the patient (10) within the skin area (22) and to determine a size measure for the blood vessel, and wherein the evaluation unit (28) is configured to evaluate a development of the determined size measure over time to derive information on the vital state of the patient (10).
