Continuous Distributions of Ventilation-Perfusion Ratios in Normal Subjects Breathing Air and 100% O2

Abstract

A B S T R A C T A new method has been developed for measuring virtually continuous distributions of ventilation-perfusion ratios (VA/Q) based on the steadystate elimination of six gases of different solubilities. The method is applied here to 12 normal subjects, aged 21-60. In nine, the distributions were compared breathing air and 100% oxygen, while in the remaining three, effects of changes in posture were examined. In four young semirecumbent subjects (ages 21-24) the distributions of blood flow and ventilation with respect to VA/Q were virtually log-normal with little dispersion (mean log standard deviations 0.43 and 0.35, respectively). The 95.5% range of both blood flow and ventilation was from VA/Q ratios of 0.3-2.1, and there was no intrapulmonary shunt (VA/Q of 0). On breathing oxygen, a shunt developed in three of these subjects, the mean value being 0.5% of the cardiac output. The five older subjects (ages 39-60) had broader distributions (mean log standard deviations, 0.76 and 0.44) containing areas with VA/Q ratios in the range 0.01-0.1 in three subjects. As for the young subjects, there was no shunt breathing air, but all five developed a shunt breathing oxygen (mean value 3.2%,) and in one the value was 10.7%. Postural changes were generally those expected from the known effects of gravity, with more ventilation to high VA/Q areas when the subjects were erect than supine. Measurements of the shunt while breathing oxygen, the Bohr CO2 dead space, and the alveolar-arterial oxygen difference were all consistent with the observed distributions. Since the method involves only a short infusion of dissolved inert gases, sampling of arterial blood and expired gas, and measurement of cardiac output and minute venti-

Pulmonary vascular dilatation and diffusion-dependent impairment of gas exchange in liver cirrhosis

“…Similarly, in two of the three patients with liver disease and arterial hypoxaemia recently reported by EDELL et al [10], the measured Pa,O 2 values were greater than those predicted by MIGET during O 2 breathing. These findings contrast with previously published studies using the MIGET analysis in both normal and patient groups breathing 100% O 2 , in whom the measured Pa,O 2 values were invariably substantially less than those predicted by MIGET [14,21,22]. In our own laboratory, using essentially the same experimental protocol and technical equipment as in the current study, we have never previously observed the measured Pa,O 2 to exceed that predicted by MIGET in a large number of both normal subjects and patients with varying lung disorders when breathing 100% O 2 [23].…”

“…In our own laboratory, using essentially the same experimental protocol and technical equipment as in the current study, we have never previously observed the measured Pa,O 2 to exceed that predicted by MIGET in a large number of both normal subjects and patients with varying lung disorders when breathing 100% O 2 [23]. Indeed, inevitable leaks in the O 2 delivery system, deterioration of the arterial blood samples prior to analysis, and insensitivity of the MIGET analysis to detect physiological postpulmonary shunt should all conspire to produce a positive P-M Pa,O 2 during 100% O 2 breathing [14,21]. Particularly in view of our limited data base, experimental error could explain our observation, the most likely sources being in the actual measurement of Pa,O 2 and/or in the MIGET analysis.…”

“…Nevertheless, it has frequently been proposed that both in health and disease, diffusion-limitation of individual MIGET gases should be readily detectable by consideration of the respective retentions (R) and blood:gas partition coefficents (i.e. l) of all six gases [14,21,27]. The theoretical basis for such an approach is that, in a homogeneous gas-exchanging lung in which there is complete alveolo-capillary inert gas equilibration, the inverse of individual gas R and l values (and corresponding logarithmic transformations ln (1-R/R) and In l) are linearly related [14,26].…”

“…The latter analysis has been described in detail by WAGNER and co-workers [14], and our application of it has been published [15]. Six inert gases (acetone, diethyl ether, enflurane, cyclopropane, ethane and sulphur hexafluoride (SF 6 ) dissolved in normal saline) were infused intravenously, and mixed venous and arterial blood was sampled from indwelling pulmonary and radial arterial catheters.…”

A Model of the Effects of Fluid Variation due to Body Position on Cheyne–Stokes Respiration

“…Mathematically this is represented asV A /Q whereV A is the ventilation (volume of gas the reaches the alveoli per unit time) andQ is the perfusion (blood flow rate which reaches the alveoli). Medical literature suggests that typically the ratio should be between 0.2 and 2.1 with a mean of one [7,15,43]. A low ratio means that there is a large amount of excess CO 2 in the lungs, which is representative of hypoventilation (very slow rate of breathing).…”