Quantitative measurement of intrapulmonary and extrapulmonary right-to-left shunt

We have developed a new technique that enables the shunting of blood from the right to the left side of the circulation to be partitioned into a cardiac and a lung component. The effects of recirculation are minimal, and the method does not require on-line data analysis. Quantitative estimates of these components have been made in two normal dogs and in five patients with raised pulmonary arterial pressures, some of whom were known to have a patent foramen ovale. The results were compared with oxygen shunt measured during air breathing. A poorly soluble gas, nitrogen, radiolabelled with 13N in solution is injected first into a central vein while matched samples of blood are drawn from the pulmonary artery and the aorta. A second solution containing 13N is injected into the right ventricle and sampled from the aorta only. Standardized gamma-counting techniques were used to analyze both the injected radioactivity and the radioactivity in the samples. These two measurements enable us to calculate the total right-to-left shunt, the pulmonary shunt, and by subtraction the extrapulmonary cardiac shunt.