The Determination of Uneven Pulmonary Blood Flow From the Arterial Oxygen Tension During Nitrogen Washout

Abstract

Many tests are available for measuring unevenness of pulmonary ventilation. In recent years tests of unevenness of pulmonary blood flow have been described, which utilize radioactive krypton (1) in patients with emphysema, radioactive oxygen in patients with mitral stenosis (2), and radioactive carbon dioxide in normal subjects (3). These studies provide quantitative data on the degree of unevenness of pulmonary blood flow but require expensive and complicated apparatus and are not easily adapted to clinical pulmonary function testing. Simpler methods of estimating unevenness of blood flow in relation to ventilation have been suggested. These are based on the rate of rise of arterial oxygen saturation (ear oximeter) during the inhalation of oxygen (4-6), analysis of gas samples obtained from various lobes of the lungs (7), continuous analysis of a single expiration (8), and the difference between the nitrogen tension of alveolar gas and urine (9, 10). These simpler methods do not provide quantitative data on the degree of unevenness of pulmonary blood flow.An ingenious graphical method of determining unevenness of perfusion of the lung in patients with chronic pulmonary emphysema has been worked out by Briscoe and co-workers (11). This method utilizes a nitrogen washout and wash-in technique and the arterial saturation (luring air-breathing. Its disadvantage is that other causes of arterial desaturation i.e., shunts and diffusion barriers cause an overestimation of the degree of unevenness of perfusion.In this laboratory we have devised a test which yields quantitative data for the determination of the fractional alveolar ventilation and pulmonary capillary blood flow that go to the well and poorly ventilated regions of the distribution of pulmonary blood flow to these regions and the anatomical shunts. The theory, method and results of these studies in normal subjects and in patients with cardiac and pulmonary disease are presented here. THEORYThe lungs can be divided into a well ventilated region (which need not be homogeneous) and a poorly ventilated region (subscripts 1 and 2, respectively). Arterial blood is a mixture of blood that has passed through these regions or through venous-to-arterial shunts. Its oxygen content (Ca) is related to the blood flows through the capillaries of the various regions (Q1, Q2) and through the shunt (Q8), and to their respective oxygen contents (Cl, C2 and Cv) as follows:Ca QT = C1 Q1 + C2Q2 + CQ9 [1] where Qi + Q2 + Qs = QT, the cardiac output. In this and subsequent formulations we omit, from our otherwise conventional (12) symbolization, the subscript c for capillary and the chemical subscript 02-It follows from Equation 1 that at any time (t) during the N2 washout:[2]Wre assume the following are constant in the later stages of the N2 washout: 1) the magnitude of the various blood flOwS (QI, Q2, Q., QT) relative to each other; 2) the arteriov5eiious 02) content difference (Ca -Cv). When we then 1 727(C. C.,) t -. 0.1.Ql + Q2

The Cause of Arterial Hypoxemia at Rest in Patients With “Alveolar-Capillary Block Syndrome”*

“…Each patient was then studied by the technique described by Finley (7) for the determination of uneven ventilation-blood flow distribution in the lungs. Briefly, the technique consists of a) continuous measurement of arterial Po.…”

Regional Emphysema of a Non-Small Cell Tumor Is Associated with Larger Tumors and Decreased Survival

“…Emphysema is associated with marked ventilationperfusion mismatch and results in worsening alveolar hypoxia (4,5). We hypothesized that emphysema in the region (not merely lobe) where a tumor occurs may result in larger non-small cell lung cancer tumors and worse overall survival.…”

Venous Admixture to the Pulmonary Circulation in Human Subjects Breathing 100 Per Cent Oxygen*

“…The role of diffusion impairment in the causation of arterial hypoxemia has been recently reevaluated ( 10), and a number of newer approaches have permitted a more precise definition of the distribution of ventilation-perfusion ratios and of its importance in gas exchange (11)(12)(13)(14)(15).…”

“…The role of diffusion impairment in the causation of arterial hypoxemia has been recently reevaluated ( 10), and a number of newer approaches have permitted a more precise definition of the distribution of ventilation-perfusion ratios and of its importance in gas exchange (11)(12)(13)(14)(15) incidence and magnitude of increased "direct" venous admixture in pulmonary disease (10,(16)(17)(18)(19). The paucity of such reports has probably been due to the lack of practical techniques for the accurate measurement of blood oxygen tension at high levels.…”