Ambulatory oxygen uptake measurement system

An apparatus for monitoring prolonged measurement of oxygen uptake without discomfort has been developed. The system is based on the open flow-through principle. The subject wears a hood through which air is drawn by an exhaust blower. Oxygen concentration is kept constantly by a servo-controlled blower, so that flow rate is essentially proportional to oxygen uptake. The flow rate of the main stream and oxygen concentration are measured. All of the equipment is assembled in a small package (wt=3 kg), which the subject carries on his back. Data are transferred from the memory to a microcomputer and an oxygen uptake trend is estimated. Response of the system to a step input is about 30 s. Compared with a commercially available oxygen monitoring system (Magna 88, P. K. Morgan Ltd., Rainham, UK), the maximum difference was 0.15 L/min within an oxygen uptake range of 0.25-2.3 L/min.