Effects of wave reflection timing on left ventricular mechanics

The aim of this study was to evaluate how the timing of the pressure pulse produced by peripheral reflection affects the left ventricle (stroke volume, ventricular work, coronary driving pressure). Ten isolated perfused rabbit hearts were attached to rubber tubes of different lengths (0.5, 0.8 and 1 m) connected to a hydraulic resistance. The different lengths produced reflections at different times and the reflected pulse returned to the ventricle in early (at 84 ms), middle (at 134 ms) and late systole (at 168 ms) for the three tubes, respectively. The loading parameters (ventricular filling pressure and hydraulic resistance) were not changed during the procedure. Ventricular and aortic pressure and aortic flow were monitored continuously and recorded; cardiac cycle was fixed at 800 ms. An operator-independent procedure was used to calculate instantaneous and total systolic external work, mean diastolic aorto-ventricular pressure difference and ventricular stroke volume. Results: The mean value of stroke volume for the three different length rubber tubes was 320±71, 348±77 and 368±87 μl, respectively. The mean value of total external work was 20.3±8.3, 22.5±8.8 and 24.2±9.6 mJ, respectively. The mean aorto-ventricular pressure difference was 40±12, 46±13, 50±14 mmHg, respectively (1 mmHg=133 Pa). The differences between the parameters measured in the three conditions were statistically significant (p<0.05). A reduction of reflection timing, reduces, on a pure mechanical basis, cardiac output and external ventricular work and has a negative effect on coronary driving pressure.