Alveolar CO2 Measured by Expiration Into the Rapid Infrared Gas Analyzer

Abstract
The normal expiratory curve of CO2 concn. shows a rapid rise as the mixed gas is expired. After the dead space is cleared the slope assumes a gentle rise of approx. 0.1% of CO2 per sec. This seems to be a function of time rather than depth of expiration. It is increased by exercise or hyperventilation. CO2 dead space was measured as 177.cc, decreasing to half after breath holding 20 sec. The expiratory curve of CO2 in a subject with advanced emphysema shows an increase in CO2 concn. with depth of expiration reaching 10% CO2. This curve is interpreted as representing gas from regions of the lung with unequal ventilation perfusion ratios and asynchronous emptying.

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