Introduction and History

Abstract

After Rahn and Fenn published A Graphical Analysis of the Respiratory Gas Exchange in 1955, understanding of the importance of ventilation-perfusion matching to pulmonary gas exchange grew rapidly. Rahn and Fenn highlighted that alveolar gas concentrations were intimately related to the associated ventilation-perfusion (${\dot{V}}_A/\dot{Q}$) ratio. Riley and Cournand expanded this into the three-compartment lung model with shunt, ideal, and deadspace compartments. This early work was important since the multiple inert gas technique (MIGET) uses the same principles of mass conservation. MIGET also built on the work of Kety, who showed that the fractional retention of an inert gas in arterial blood was function of solubility and ${\dot{V}}_A/\dot{Q}$ ratio. Later, Farhi and Yokoyama devised a method for measuring retention of inert gases during washout, from which a two-compartment model of ${\dot{V}}_A/\dot{Q}$ inequality was derived. Lenfant and Okubo exploited the fact that arterial partial pressure of oxygen (${P}_{{\mathrm{O}}_2}$) response to inspired O₂ depended on the ${\dot{V}}_A/\dot{Q}$ ratio and modeled a continuous distribution of ${\dot{V}}_A/\dot{Q}$ ratios to compute the underlying ${\dot{V}}_A/\dot{Q}$ ratios explaining the response. Using computer algorithms to solve the gas exchange equations of these pioneering investigators and to quantify the O₂ and CO₂ dissociation curves, Kelman, Olszowka, and West studied complex gas exchange behavior by taking theoretical ${\dot{V}}_A/\dot{Q}$ distributions and evaluating the effect on O₂ and CO₂ exchange. Wagner and West working with Saltzman realized that by using the inert gas approach of Farhi and Yokoyama, and measuring the elimination, simultaneously, of several inert gases of widely varying solubility, continuous distributions of ${\dot{V}}_A/\dot{Q}$ could be measured. This is what gave rise to the multiple inert gas elimination technique.