Measurement of patient's oxygen consumption rate - includes addition of measured quantity of pure oxygen to expired air to restore normal level in mixture

摘要

The patient (3) breathes in and out through a first (1) and second pipe (2), with non-return valves (1a, 2a) ensuring that air flows in the required direction only. The second pipe (2) opens into an enclosure (4) of sufficient size that gas flows continuously out through the outlet (5). A further supply (7) of the gas being monitored (oxygen or carbon dioxide) is fed through a control valve (8) with a flow meter (10) attached to the outlet (5). A sensor in the outlet pipe senses the concentration of the detected gas in the mixed output of air. The signal produced is proportiona to this concentration, and is fed to a caomprator (12) whose other input is a reference value. The comparator output is fed to the valve (9) control. The valve (8) is thus regulated to eliminate any difference signal from the comparator. The reading on the flow meter then indicates the rate at which gas is used by the patient.