Distribution function of pulmonary blood flow and ventilation-perfusion ratio in man.

Abstract

The distribution function of pulmonary blood flow was determined in 5 healthy subjects and 5 patients showing signs of diffuse obstructive pulmonary syndrome. The method used is based on the fact that at any time the mixed arterial O2 content is related to the blood flow through the various compartments and to the respective O, contents. A procedure is described to overcome the alinearity of the O2 dissociation curve. The rate of increase in O2 content during a lung N2 washout is represented by the superposition of an infinite number of double exponential functions. The blood flow distribution as a function of clearance time constant was obtained with the aid of an iteration procedure and from the inversion of the Laplace transform by an approximation method. The comparison of this distribution function with that of ventilation and pulmonary lung volume lead to the construction of the continuous distribution of blood flow and lung volume as a function of VA/Q [ventilation/per-fusion]. In both groups of subjects a relative underperfusion of the low VA/Q units is almost consistently observed. This is viewed as an adjustment which limits the hypoxia in patients.