Noninvasive cardiac output determination using inhaled oxygen-15-labeled carbon dioxide

Inhaled oxygen-15-labeled carbon dioxide (CO2*) is hydrated in the alveolar capillary blood to produce oxygen-15-labeled water (H2O*). This allows noninvasive delivery of a traceable indicator into the pulmonary circulation. Removal of oxygen-15 marker from the lung is a function of pulmonary perfusion. Two techniques were evaluated for computing cardiac output (CO) following single bolus inhalation of CO2*: 1) continuous monitoring of arterial blood activity through an external detector and 2) noninvasive positron imaging of oxygen-15-label washout from the chest and simultaneous emergence of activity in arterial blood. In seven mongrel dogs studied using technique 1, 46 determinations of CO were made from 1.2 to 8.0 l/min and compared with simultaneous indocyanine green dye-dilution determination. Correlation coefficient was 0.90 with slope of linear regression of 1.05. In 12 mongrel dogs studied using technique 2, 23 determinations of CO were made from 0.9 to 9.2 l/min and compared with simultaneous indocyanine green dye determination. Correlation coefficient was 0.985 (P less than 0.001) with slope of linear regression of 0.898. This noninvasive technique (2) for determination of CO is independent of assumptions regarding regional ventilation or perfusion of the lung and appears valid in animal studies.