Rate of generation of myocardial power density normalized by cardiac frequency.
We introduce a frequency normalized, power averaged, rate of generation of power density (FARPD) that extends the range of applicability of the averaged rate of generation of power density (ARPD) to any cardiac frequency encountered in experimental or clinical situations. Normalization eliminates the frequency-dependent mathematical artifacts arising during the computation of quantities containing time derivatives of the pressure, while preserving the effects of changes in heart rate on the cardiac muscle itself (Bowditch type of phenomena). The distribution of normal values in a group of 51 control dogs was very close to the standard normal distribution. These values had no statistically significant differences with those of a smaller control group studied by independent investigators. Isoproterenol and propranolol produced highly significant statistical changes in FARPD. Alterations in pre- and afterload produced changes that were not significant for the former and significant at the 5% level for the latter. These changes were small when compared to those resulting from typical inotropic interventions.