[A method to predict pulmonary blood flow by nitrous oxide washout curve]

The study was performed to obtain a relationship between the pulmonary blood flow and the tau b (time constant) calculated from multiple-breath nitrous oxide (N2O) washout curve. Elimination of N2O depends on pulmonary blood flow and alveolar ventilation. From the theoretical consideration, tau b can be calculated by the following formula; tau b = Vd[1/Qt-Qs) + 0.47/VA) Vd = N2O volume of distribution in the body Qt = cardiac output, Qs = shunt blood flow VA = alveolar ventilation. Relationship between observed Qt-Qs and observed tau b was admitted to the predicted formula. The method was compared with the thermodilution method in almost simultaneous measurement of the cardiac output. A good correlation was obtained between them (r = 0.87). Washout curve of nitrous oxide can be used for a reliable measurement of pulmonary perfusion.