抄録
A new approach has been developed for evaluating uneven distribution of ventilation/perfusion ratio, VA/Q, based on a two-compartment model with a reciprocal VA/Q relation. TheVA/Q ratios were expressed by μ•(1-ρ)/ρ and μ•ρ/(1-ρ), where μ and ρ were referred to as the "ideal" VA/Q ratio and unevenness factor, respectively. During steady state breathing, arterial blood was analyzed for PO2 and PCO2, and end-tidalPCO2 as well as the gas exchange ratio, R, was measured. After steady state breathing a rebreathing experiment was performed, and the arterial-venous O2 content difference, (a-v) CO2, was measured, and then, multiplying it by R, the venous-arterial CO2content difference, (v-a) CCO2, was obtained. Referring to these values the mixed venous PO2 and PCO2 were estimated from arterial PO2 and PCO2, using the O2 and CO2 dissociation curves. TheVA/Q line and iso-R line were drawn to find μ, and further, total arterial, and alveolar PO2 and PCO2 of the two-compartment model were computed by changing both ρ and the mixing weight factor, Φ. The Φ value was determined so as to make the abovePO2-PCO2-locus pass through the measured arterial PO2 and PCO2. The ρ value was selected so that the computed alveolar PCO2 fitted to the end-tidal one. The experiments were performed on 8 normal subjects in normoxia and hyperoxia with PIO2 245Torr. The mean .Φ values in normoxia and hyperoxia were 0.50 and 0.56, respectively. The mean ρ values in normoxia and hyperoxia were 0.438 and 0.428, respectively. The VA/Q ratio was decreased in hyperoxia because of a decrease inVA value.
