Left ventricular diastolic suction with zero left atrial pressure in open-chest dogs

We investigated left ventricular (LV) diastolic volume changes (suction inflows) with left atrial pressure (LAP) clamped to ambient pressure in six open-chest, anesthetized dogs. The left atrium was cannulated and connected to a servo pump, and LAP was clamped to a set point near 0 mmHg for four beats by withdrawing blood. LAP averaged 5.88 ± 1.44 mmHg before the clamp and fell to 0.74 ± 0.61 mmHg (P < 0.0001) after the clamp. During the first clamped beat a transmitral pressure gradient of 1.0 ± 0.6 mmHg was observed, resulting in LV filling of 2.6 ± 1.8 ml. Subsequent beats developed suction-driven (mean negative LV pressure: -1.5 ± 1.3 mmHg; P < 0.005 vs. zero) LV filling of 4.5 ± 2.8 ml/beat with a peak transmitral pressure gradient of 1.7 ± 0.6 mmHg. These data are consistent with the hypothesis that LV suction can be an important filling mechanism under conditions in which LV end-systolic volume is reduced, e.g., reduced filling pressures, high heart rates, exercise, or increased inotropic drive.