Abstract: A new method and a device are disclosed to determine physiologic parameters of a subject by analyzing it's breathing gas with an electrochemical sensor. The measured components of the breathing gas allow for many conclusions about the condition of the subjects's pulmonary system. It is therefore an objective of this invention to determine physiologic parameters from measuring the partial pressure of oxygen in the mainstream of the breathing gas. According to the invention the measurement can be performed non invasive and allows for conclusions about the respiratory and metabolic system of a subject. The invention makes a continuous measurement of the oxygen partial pressure possible, that almost shows no time delay. The invention allows for instance the determination of parameters like the oxygen concentration in the breathing gas, the oxygen consumption of the subject, the heart frequency, the respiratory quotient, the compliance of the pulmonary tract and other physiologic parameters.