CHARACTERISTICS OF SINGLE ISOVOLUMIC LEFT-VENTRICULAR PRESSURE WAVES OF DOG HEARTS IN-SITU

By fitting isovolumic phases of an ejecting beat with a model-wave fun ction, one can predict source pressure of the ejecting beat (Sunagawa et al. Trans Biomed Eng 1980; 27:299-305), this being a major determin ant of systolic performance. Prior applications of this principle have involved two assumptions: (1) that the isovolumic pressure wave is sh aped like an inverted cosine wave, and (2) that duration of an isovolu mic beat is the same as that of an ejecting beat. The first assumption might cause overestimation of source pressure, since an isovolumic pr essure wave begins declining before the midpoint of the wave. The seco nd assumption might cause underestimation of source pressure, since an ejecting beat is always shorter than an adjacent isovolumic beat at t he ejecting beat's end-diastolic volume. Although the two errors tend to cancel, it would be more rational and accurate to use a realistic m odel wave shape and a realistic isovolumic beat duration. To acquire t he information necessary for this, pressure and volume time courses we re measured during ejecting beats and adjacent isovolumic beats in dog s under the following steady-state conditions: basal, atrial pacing at various rates, infusion of dobutamine, infusion of verapamil, coronar y ligation(s), and ventricular pacing at various sites. These conditio ns affected the amplitude and duration of isovolumic pressure waves su bstantially but did not affect the shape of the waves significantly. T he duration of each isovolumic beat exceeded that of the previous ejec ting beat to a degree which corresponded approximately to the ejecting beat's normalized pressure reserve (source pressure minus peak ejecti on pressure)/(source pressure). A more accurate source-pressure predic tion should be possible by use of a realistic isovolumic pressure-wave shape and by taking account of the effect of pressure reserve on cont raction duration.