Cardiac Output in Healthy Subjects Determined with a CO2Rebreathing Method

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Abstract
The cardiac output is measured with a CO2rebreathing method suggested by Defares(1956). The mixed vmous CO2pressure is determined graphically from the breath by breath‐determined CO2content in a rubber bag during rebreathing from the bag. Arterial CO2pressure is assumed to be the same as in end‐tidal air. CO2eliminated per time unit is measured by collecting the expired air in a Douglas bag and the cardiac output is determined with the Fick equation. For the CO2analysis a rapid infrared CO2metcr is used. The obtained values at rest are of the same size as those obtaincd with the Crollman acetylene method. The values from the work cxperiments arc of the same magnitude as those obainted with dye‐diliution or direct Fick methods. Stroke volume shows increasr from rrst to work about 60–80 per cent.