Validation of a two-compartment model of ventilation/perfusion distribution.

Ventilation (V (A)) to perfusion (Q ) heterogeneity (V (A)/Q ) analyses by a two-compartment lung model (2C), utilizing routine gas exchange measurements and a computer solution to account for O(2) and CO(2) measurements, were compared with multiple inert gas elimination technique (MIGET) analyses and a multi-compartment (MC) model. The 2C and MC estimates of V (A)/Q mismatch were obtained in 10 healthy subjects, 43 patients having chronic obstructive pulmonary disease (COPD) and in 14 dog experiments where hemodynamics and acid-base status were manipulated with gas mixtures, fluid loading and tilt-table stressors. MIGET comparisons with 2C were made on 6 patients and 32 measurements in healthy subjects before and after exercise at normoxia and altitude hypoxia. Statistically significant correlations for logarithmic standard deviations of V (A)/Q distributions (SD(V (A)/Q )) were obtained for all 2C comparisons, with similar values between 2C and both other methods in the 1.1-1.5 range, compatible with mild to moderate COPD. 2C tended to overestimate MC and MIGET values at low and underestimate them at high SD(V (A)/Q ) values. SD(V (A)/Q ) weighted by Q agreed better with MC and MIGET estimates in the normal range, whereas SD(V (A)/Q ) weighted by V (A) was closer to MC at higher values because the V (A)-weighted SD(V (A)/Q ) is related to blood-to-gas PCO(2) differences that are elevated in disease, thereby allowing better discrimination. The 2C model accurately described functional V (A)/Q characteristics in 26 normal and bronchoconstricted dogs during non-steady state rebreathing and could be used to quantify the effect of reduced O(2) diffusing capacity in diseased lungs. These comparisons indicate that 2C adequately describes V (A)/Q mismatch and can be useful in clinical or experimental situations where other techniques are not feasible.