Measurement of the Distribution of Pulmonary Blood Flow by 85kr in Solution

Biologically inert radioactive gases, introduced in solution into the blood stream, have proved to be a very valuable means of investigating pulmonary circulation. This is due to their partition coefficient, which is such that in the lungs the tracer leaves the blood phase and goes into the gas phase. The use of 85Kr in connection with bronchospirometry has therefore made possible quantitative study of the effects of hypoxia and/or hypercapnia on pulmonary vasomotricity and hence on the flow distribution of the lesser circulation. The technique consisted in injecting into a vein a small volume of 85Kr in solution, collecting the gas exhaled from each lung and measuring its radioactivity. Cardiac flow and the partial pressures of the respiratory gases of the pulmonary and peripheral arterial blood were measured at the same time. By varying the oxygen content of the mixture inhaled by one of the lungs, a more or less pronounced local hypoxia was induced. Similarly, it was possible to combine hypercapnia, hyperoxia and homolateral or contralateral hypoxia. Finally, various processes were used to modify separately the pH and the partial pressure of carbon dioxide (PCO2). A comparison of the results obtained on 118 subjects shows that the hypoxic stimulus acts progressively, and that the ratio perfusion of hypoxic lung/perfusion of normoxic lung is linearly related to the PO2 of the alveolar gas and/or the pulmonary venous blood. The slope of the straight line representing this relationship depends on the local PCO2 (of alveoli and/or pulmonary venous blood), which has little vasoconstrictive action on the lung circulation in normoxia but has an increasing effect with a more pronounced hypoxia. (author)