140 CONTINUOUS COMPUTERIZED DIASTOLIC PRESSURE ANALYSIS (DPA) IN NEONATES

Abstract

DPA and determination of an aortic diastolic time constant, τ, has been utilized to evaluate two groups of neonates: the first with left to right ductal shunting; and the second with no ductal shunting. In earlier studies performed manually, τ, which is the reciprocal of the slope of the log of the diastolic pressure plotted against time, was 400 ± 57 msec (1 S.D.) in group I and 657 ± 62 msec in group II. A microcomputer system suitable for continuous τ determinations is described. Arterial pressure pulses are obtained from umbilical aortic catheters which are connected to a standard amplification system. The analog signal is then transmitted to an analog-to-digital convertor of a microcomputer which samples at the rate of 100 times/sec. These data are then used to determine the instantaneous slopes between successive samples on each pressure cycle to enable the automated recognition of the dicrotic notch and the onset of systole. Once the diastolic portion of each beat is identified and meets certain quality criteria, eight equally spaced points are selected in diastole and a least squares fit is made to an exponential curve and the τ is determined. Current on-line τ determinations are performed over 25 second intervals every ten minutes and the mean τ and standard deviation are recorded. Subsequent trend analysis as a means to determine the predictive value of τ is anticipated.