Computer processing of transaortic valve blood pressures in the horse using the first derivative of the left ventricular pressure trace

A method is described of processing transaortic valve pressures in the horse using the first derivative of the left ventricular pressure to define the beginning and end of each systolic complex. To determine the beginning of each systole three definitions of left ventricular end diastolic pressure (LVEDP), based on a 100, 150 or 200 mmHg/sec rate of left ventricular diastolic pressure rise, were evaluated. These definitions were also evaluated for their ability to determine isovolumic contraction time (ICT) and pulse interval. The best of these, LVEDP 150, was defined as the last point in diastole before a rate of rise of left ventricular pressure (LVdP/dt) equal to or exceeding 150 mmHg/sec sustained over 44 msecs. The end of left ventricular ejection was estimated from the left ventricular pressure trace as the point at which--LVdP/dtmax occurred. There was good agreement between the values of left ventricular ejection time (LVET) measured to the incisura of the aortic pressure trace and LVET calculated to the time of--LVdP/dtmax (r = 0.991). The importance of visually examining the waveforms before committing them to automatic processing is emphasised.