Analysis of rebreathing measurements of pulmonary tissue volume in pulmonary edema

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Abstract
A rebreathing method (using C18O and C2H2) for the estimation of pulmonary tissue and capillary blood volume (VTPC) was evaluated in 13 dogs. In 7, pulmonary edema was induced by oleic acid injection. Six dogs served as controls. Values of VTPC calculated by 3 algorithms were compared to postmortem lung water. The 1st algorithm uses the C18O intercept to determine time 0 and all data to construct the alveolar disappearance curves. The 2nd uses the beginning of inspiration as time O. The last uses data only during the last 3rd of expiration. The best correlation (r = 0.90) between VTPC and total lung water was obtained utilizing the 1st algorithm. In the control animals, mean VTPC was 188 ml and in the edema dogs was 278 ml. Mean VTPC for all dogs was 96 .+-. 14% of total lung water using the 1st algorithm. Another algorithm was evaluated in the edema dog group. This method gave values of VTPC 53% higher than those obtained by the 1st algorithm.