Article révisé par les pairs
Résumé : The left-to-right shunts increase the oxygen content in the right heart, but it may he difficult to reveal these changes in small shunts, whose theoretical and practical interest must he emphasized however. During deep and rather quick breathing of a gas mixture with a high nitrous oxide concentration, the N20 content rapidly becomes very important in the arterial blood and, so. in the shunted blood, while it begins to increase slowly in the normal venous blood; thus, if simultaneous samples are then obtained from the systemic artery and from the right heart, and if the level in the lallcr is expressed as percentages of the level in the former, the results are very low when there is no shunt: since the arterial eontent is of course lOO/o, a very small shunt gives relatively high percentages in the right heart. The synchronism of the samples, the similitude of the content in the various veins and the large arteriovenous difference justify the interest of the method. The evolution of the arterial and venous N20 levels was analysed in normal patients and in left-to-right shunts; the results have led to important changes in the technics described by other authors: these changes chiefly concern the timing of the sampling (from the 5th to the 15th second of the N20 breathing), the N20 concentration in the gas mixture (N20 79% and 02 21%), the technic of the sampling (emptying of the catheter up to the beginning of the sampling), and finally the “blank” determination (sampling when breathing 02 100%). The normal levels, observed in the right heart and the pulmonary artery of 40 patients, were-1.3 to 6.9% (mean 1.9% SD = 1.7%58 tests); these values, small and very close together, indicate the sensitivity of the technic. 15 patients with a left-lo-right shunt had levels between 10 and 82.9% (mean 40,9%- 16 tesls); the relative increase is quite evident. :t tesls, performed in a left ventricle, a left auricle and a pulmonary vein, showed the precision of the method (99.9-100.0 and 100.2%). Finally, the relative errors due to the analysis become negligible as a result of the absolute content in the systemic arteries (2.08 to 19.77 vo!.%, mean 11.82-77 tests). According to these characteristics, a venous level higher than 7% of the arterial level is abnormal, and the method should reveal lefl-to-riglil shunts about 5-10% of the systemic output. The iffiiocuity and the practical .simplicity of the method are emphasized, for it requires only a classical right heart catheterization and an usual apparatus. © 1961 S. Karger AG, Basel.