STUDIES OF CYCLOPROPANE Iv. CARDIAC OUTPUT IN DOGS UNDER CYCLO- PROPANE ANESTHESIA

Since the introduction of cyclopropane as an anesthetic agent by Lucas and Henderson (1) in 1929, the question of deleterious action upon the heart had been present in the minds of most laboratory investigators and clinical anesthetists. This possibly harmful action was first suggested by Lucas and Henderson be-cause of the definitely toxic action of propylene, an isomer of cyclopropane, shown by Caine and Reynolds in 1926 (2). In an investigation by Seevers et al. (3) in 1934, it was found that at the time of or after respiratory arrest marked changes occur in the heart of dogs anesthetized with cyclopropane as shown by electrocardiographic records. They also found that when artificial respiration was instituted, the rhythm returned to normal and that the concentration of cyclopropane in the in-spired air could be further increased without the recurrence of arrhythmias until the concentration reached 60 per cent or more. Kurtz, Bennett, and Shapiro (4) in 1936 reported their findings of an electrocardiographic study on 109 patients during surgical anesthesia produced by various anesthetic agents including cyclo-propane. Similar changes were found with each anesthetic agent, but the frequencies of the various abnormalities varied with the different anesthetics. Displacement of the pacemaker occurred in approximately 60 per cent of the patients under ether and nitrous oxide and in 48 per cent of the patients anesthetized with cyclopropane; ventricular extrasystoles were recorded in 55 per cent of the patients under cyclopropane anesthesia and i