Determination of extravascular lung water by dilution method. II. Technique and results in dog and man

Central venous injection of tritiated water and albumin labelled with 131I and simultaneous sampling from pulmonary artery and aorta enabled us to calculate extravascular lung water both from extrapolated aortic curves (idQw1) and from the calculated transfer function of water transit times in the extravascular lung space (idcQw1). In 4 control dogs, extravascular lung water found post-mortem, Qw1, averaged 5.6±1.1 ml/kg, idcQw1 5.6±1.5 ml/kg and idQw1 3.8±2.3 ml/kg. In 3 dogs with acute increase of pulmonary microvascular pressure (mean pulmonary artery pressure was 44.0±8.9 mmHg after left ventricle overload), Qw1 averaged 15.5±6.6 ml/kg, idcQw1 16.8±9.8 ml/kg and idQw1 13.6±9.0 ml/kg. In 7 observations in man with diastolic pulmonary artery pressure (DPAP) 14 mmHg or below (DPAP=10.7±3.1 mmHg), idcQw1 was 5.5±1.0 ml/kg and idQw1 3.2±0.9 ml/kg; the normal value reported in the literature for Qw1 being 5.4 ml/kg. In 10 observations in man with DPAP above 14 mmHg (DPAP=23.7±9.3), idcQw1 averaged 9.3±3.8 ml/kg and idQw1 4.3±1.9 ml/kg. The good correspondence of Qw1 and idcQw1 indicates that the latter provided an accurate measure in vivo of the actual content of extravascular lung water in dogs under different hemodynamic conditions. This appears to be true also in man. On the contrary, the double extrapolation method detected only a fraction of idcQw1 and Qw1 (idQw1 was 69% of idcQw1 in dogs and 54% in man). Such underestimation tends to increase where extravascular lung water increases: in 5 patients in whom measurements were done during edema and after recovery, idQw1 averaged 40% and 62% of idcQw1, respectively. The possible explanation for this underestimation and of the discrepancy between dogs and human studies are discussed. The input-output principle applied in this paper can be of practical value for: calibrating simpler methods of assessing pulmonary edema in vivo, and investigating the capillary permeability of the lung and other vascular districts.