EFFECT OF CYCLOPROPANE AND HALOTHANE ON VENTRICULAR MECHANICS; A CHANGE IN VENTRICULAR DIASTOLIC PRESSURE-VOLUME RELATIONSHIPS

¹ Cardiovascular Research Institute and Departments of Medicine and Anesthesia, University of California School of Medicine, San Francisco, California, and The Department of Anesthesia, University of Iowa College of Medicine, Iowa City, Iowa

We compared the effects of cyclopropane and halothane on ventricular mechanics in dogs. The agents were given in concentrations which produced similar depressions of cardiac output. Very high concentrations of cyclopropane were associated with marked alterations in left ventricular diastolic pressure-volume relationships; extremely high end-diastolic pressures were observed without changes in end-diastolic volume, resulting in a marked decrease in calculated ventricular diastolic compliance. In contrast, high concentrations of halothane produced no significant change in left ventricular end-diastolic pressure at a time when end-diastolic volumes slightly increased. Arterial pressure was better maintained with maximum concentrations of cyclopropane than with halothane. Despite this, the increasing metabolic acidosis during cyclopropane anesthesia suggests that perfusion of the organism was less well maintained. Ventricular performance should not be evaluated from end-diastolic pressures alone; diastolic compliance and therefore diastolic fiber length can also vary. Increased ventricular rigidity may explain the high venous pressures noted clinically with cyclopropane anesthesia.