Reliability of the maximum derivatives of left ventricular pressure and internal diameter as indices of the inotropic state of the depressed myocardium.

The effects of inotropic stimulation and increases in end-diastolic diameter, aortic pressure, left ventricular end diameter size, mean arterial pressure, and heart rate on maximum rate of change of left ventricular pressure (dP/dtmax) and diameter (dD/dtmax) were studied in eight dogs. Responses were studied in the normal conscious state, during myocardial depression due to high doses of pentobarbital or propranolol, and after bilateral cardiac sympathectomy. In all states studied, both dP/dtmax and dD/dtmax were substantially augmented by inotropic stimulation with isoprenaline and were less influenced by changes in end-diastolic diameter, mean arterial pressure and heart rate. It is concluded that both indices are highly sensitive to the contractile state of the left ventricle and relatively insensitive to haemodynamic alterations in both normal and depressed hearts.