Pulsatile uptake of CO in the human lung

The instantaneous uptake of CO in the lungs was measured with a water-filled body plethysmograph in normal man. First, control measurements of plethysmograph pressure were made while the subject held his breath for 7 sec after breathing gas mixtures prepared to bring his alveolar P(O2) and P(CO2) close to mixed venous levels. Then, CO uptake measurements were made while he held his breath after inhaling the same gas mixtures with added CO (2.0%). The change in lung volume on CO minus the change in lung volume during the control measurement was a measure of the CO uptake in the lungs. Cardiopneumatic changes in lung gas volume were subtracted electrically. All of five subjects showed pulsatile CO uptake. The mean CO uptake was 103 ml/min. A peak uptake of 2.0 (range 1.6-2.3) times the mean uptake occurred 0.3-0.4 sec after the R wave of the EKG and a minimum uptake of 0.4 (range 0.2-0.5) times the mean uptake occurred during the tenth of a second before the R wave of the EKG. These results suggest that pulmonary capillary blood volume is pulsatile during the cardiac cycle.