To investigate whether the central blood volume (CBV) reflects the pulmonary vasculature, we measured CBV before and after the inhalation of 100 % or 13 %O2 for 15 min in patients with chronic pulmonary diseases. Using the Stewart-Hamilton technique, we measured CBV using a lung water computer, employing sodium as an indicator. Thirteen patients inhaled 100 % O2, while 8 patients breathed 13 % O2. Hyperoxia increased CBV significantly and the delta change in CBV(△CBV)correlated significantly with the change in total pulmonary resistance index(△TPPI;r=-0.65, p<0.02),the change in mixed venous oxygen tension(△PvO2; r = - 0.58, p < 0.05) and the change in the coefficient of oxygen delivery (△COD;r=0.71, p<0.02). Hypoxic breathing caused little or no change in CBV, but △CBV correlated well with△TPRI(r=-0.74, p<0.05)and△PvO2 (r=0.85,p<0.01)。 Our results suggest that△CBV provides a good index of the pulmonary vascular bed, on which efficient gas-exchange occurs
