In conscious dogs, the isovolumic index (dP/dt)/DP40 is sensitive to acute inotropic changes and less sensitive to LVEDP changes, though it performs poorly at very low LVEDP and shows wide basal variation.
Left ventricular function and isovolumic indices of contractility were examined in the awake, chronically instrumented dog to assess their ability to detect changes in inotropic state, and their response to changes in left ventricular end-diastolic pressure (LVEDP). During the initial 8–10 beats following inferior vena cava (IVC) occlusion, the relation between stroke volume and LVEDP exhibited substantial variations in the basal state and, although useful for defining acute responses to isoproterenol (1 μk), it did not detect a response to propranolol (0-· mg/kg). Of the many isovolumic indices examined in the index (dP/dt)/DP at a developed LVP of 40mmHg (dP/dt)/DP40 offered the least scatter and sensitivity to LVEDP changes and it was sensitive to acutely induced changes in inotropic state. However, this ratio and other isovolumic indices responded poorly to contractility changes originating from LVEDP levels below 4 mmHg. Moreover, its basal level exhibited wide variation in the same animal on different days and in different normal animals.
Davidson et al. (1974) studied this question.