Abstract: Device for the measurement of oxygen consumption which, by use of a mixing chamber of small dimensions, allows compensation of the time delay between the measurement of the ventilation VE and that of average oxygen concentration of the exhaled air volume FeO2. The time delay between measurement of VE and FeO2 maintains a constant value under all ventilations, thanks to a dynamic control of the air quantity collected and introduced in the microchamber and to a dynamic update of proportion factor K, performed by a control system. This enables a precise measurement of oxygen consumption also with rapid ventilation changes.