THE MEASUREMENT OF CARDIAC OUTPUT. AN IMPROVEMENT OF THE ACETYLENE METHOD PROVIDING AN INHERENT CHECK

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Abstract
By modification of the apparatus described by Marshall and Grollman for the detn. of arteriovenous O2 difference, to permit the collection of multiple samples of "alveolar" and "bag" gas, it is possible to identify the establishment of lung-bag equilibrium of the acetylene-air mixture and the beginning of recirculation of acetylene-containing blood to the lungs in each instance. Analytical inaccuracies and leaks, as well as most of the many irregularities encountered in a procedure of this type, are identified. The time required to achieve lung-bag equilibrium and the time of the first appearance of recirculation are variable, but they usually occur much earlier in the period of rebreathing than Grollman indicated. The interval between the establishment of equilibrium and the occurrence of recirculation varies, but is usually long enough to allow at least 2 complete respirations. This is sufficient for an accurate detn. of arteriovenous O2 difference. 76% of 82 detns. were in error by less than 7.5%.

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