[Methods for the determination of VA/QC ratio].

Physiological considerations relevant to a general understanding of the question are put forward and the main methods used for determining the ventilation-perufsion ratio are described. Over-all methods offer generic evaluation of a change, particularly the method whereby the alveolus/arterial PO2 gradient is measured on straight lines expressing the different points of gas and blood respiratory exchanges, and that which measures the triple CO2, O2 and N2 alveolus/arterial gradient. Methods employed to evaluate the distribution of ratio changes are also explained: evaluation with CO2 labelled with 15O2, 133Xe, 13N2 and 85Kr, using pairs of scintillators, scanning detectors, gamma camera or special cuvettes, and analysis of respiratory He, Ar, O2, CO2, N2O and CHF2Cl at the mouth and inside the lung, using rapid analysers and single or multiple breath methods, or analysis of gas elimination coefficients. It is felt that measurement of the VA:Qc ratio is now within the capacity of all laboratories, so that qualitative, semi-quantitative and quantitative assessment can be made not only of the ability to ensure efficient alveolar exchange on the part of ventilation and circumation, but also of the presence of compensated changes, or the simultaneous presence of other alterations of various kinds, which cannot be readily detected by using conventional methods.