[Simultaneous analysis of the distribution of ventilation and diffusive conductance to perfusion in the lungs]

Theoretical analysis and experimental observations were performed to establish an essential method allowing demonstration of the characteristics of distribution of ventilation (VA) as well as of diffusive conductance (G) to perfusion (Q) in the lungs. O2, CO2 and CO binding to hemoglobin molecules within erythrocytes, together with six inert gases including SF6, ethane, cyclopropane, halothane, diethyl ether and acetone, possessing various degrees of solubility in blood and different degrees of diffusibility in lung tissue were used as indicator gases. Fifteen patients with interstitial pneumonia of unknown etiology, placed in a supine position, were given a mixture of 21% O2 and 0.1% CO in N2 as the inspired gas and normal saline containing appropriate amounts of the six inert gases via the antecubital vein. After a steady state was established, the expired gas was collected and both arterial and mixed venous blood were simultaneously sampled through the catheter inserted either into the femoral or pulmonary artery. The concentrations of the indicator gases in the samples were measured by gas chromatography, with electrodes or with Scholander gas analyzer. Assuming that the mass transfer efficiency of a given indicator gas at each gas exchange unit would be limited by the ratio of VA to Q (VA/Q) and by that of G/Q, the data obtained from the human subjects were analyzed in terms of a lung model having 20 units along the VA/Q and G/Q axes, respectively. The numerical analysis including the procedure of a simultaneous Bohr integration for O2, CO2 and CO in a pulmonary capillary and the method of weighted least-squares combined with the idea of constrained optimization permitted the data to be transformed into a virtually continuous distribution of Q against VA/Q and G/Q axes. The numerical procedure was strictly tested based on many artificial distributions of VA/Q and G/Q ratios, showing that it could characterize distributions containing up to at least two modes in the VA/Q-G/Q field with a substantial accuracy. Analytical results estimated from the patients with interstitial lung disease revealed: 1) most of the lung is operating in the range of normal VA/Q in an early stage of their illness, while widening of VA/Q distribution accompanied with a significant contribution of both high and low VA/Q areas is observed in an advanced stage of the disease.(ABSTRACT TRUNCATED AT 400 WORDS)