A method for non-invasively determining at least one physiological parameter based on a vascular blood flow and/or volume in a thoracic bone or a sternum of a subject, said method comprising: providing a sensor comprising at least one light source and at least one detector adapted to be arranged at a skin site of said thoracic bone or said sternum of said subject, wherein said light source comprises two near-infra-red LEDs (41a-b) having a wavelength in the range of 800 to 810 nm, and two red LEDs (42a-b) having a wavelength in the range of 640 to 680 nm, and said detector comprises four photodetectors (40a-d), said LEDs and said photodetectors arranged in a double lining configuration to cover vessels emerging from left and right internal thoracic arteries and its corresponding collecting veins, wherein the length of said sensor correlates to the volume of blood covered during a measurement, and wherein the optical geometry of the LEDs and photodetectors is arranged so that the light can penetrate and reach the vessels in the thoracic bone or in the sternum bone; transmitting light from said at least one light source to said thoracic bone or sternum; detecting at least a part of said transmitted light being reflected and/or scattered by blood vessels in said thoracic bone or said sternum; analysing and evaluating said reflected and/or scattered light detected by said at least one detector for determining said at least one physiological parameter, wherein the at least one physiological parameter comprises oxygen saturation SaO2 (%) in the sternum bone, which is determined by a quotient between total light reflection and/or scattering of said near-infra-red wavelength and said red wavelength. providing a sensor comprising at least one light source and at least one detector adapted to be arranged at a skin site of said thoracic bone or said sternum of said subject, wherein said light source comprises two near-infra-red LEDs (41a-b) having a wavelength in the range of 800 to 810 nm, and two red LEDs (42a-b) having a wavelength in the range of 640 to 680 nm, and said detector comprises four photodetectors (40a-d), said LEDs and said photodetectors arranged in a double lining configuration to cover vessels emerging from left and right internal thoracic arteries and its corresponding collecting veins, wherein the length of said sensor correlates to the volume of blood covered during a measurement, and wherein the optical geometry of the LEDs and photodetectors is arranged so that the light can penetrate and reach the vessels in the thoracic bone or in the sternum bone; transmitting light from said at least one light source to said thoracic bone or sternum; detecting at least a part of said transmitted light being reflected and/or scattered by blood vessels in said thoracic bone or said sternum; analysing and evaluating said reflected and/or scattered light detected by said at least one detector for determining said at least one physiological parameter, wherein the at least one physiological parameter comprises oxygen saturation SaO2 (%) in the sternum bone, which is determined by a quotient between total light reflection and/or scattering of said near-infra-red wavelength and said red wavelength.