The first derivative of the transthoracic electrical impedance as an index of changes in myocardial contractility in the intact anaesthetised dog.

The suitability of the peak value of the first derivative of the thoracic electrical impedance dZ/dtmax has been investigated in dogs as a non-invasive index of changes in myocardial contracility by comparing if with the peak left ventricular dP/dt and the peak values of aortic blood velocity and acceleration. An increase in the inspired halothane concentration was used to produce changes in contracility. In 5 dogs the combined values for the correlation coefficient between dZ/dtmax peak velocity and acceleration were respectively 0.937, 0.954 and 0.950. In 14 out 15 comparisons p less than 0.001 and in one, p less than 0.01. On these grounds, dZ/dt max is proposed as a variable worthy of sconsideration in patient monitoring.