Left ventricular contractility using isovolumic phase indices during PEEP in ARDS patients

The effects of incremental increases in PEEP during mechanical ventilation on left ventricular (LV) contractility before and after intravascular volume expansion (IVE) were studied in 10 patients treated for ARDS. A pulmonary artery (PA) catheter, a LV catheter-tip micromanometer, and an esophageal balloon catheter were inserted in these patients. We measured transmural right atrial and PA pressures, transmural LV end-diastolic and systemic arterial pressures, the first derivative of LV pressure (LV dP/dt), the ratio of LV dP/dt at transmural developed LV pressure (dP/dt/DPt) with DPt = 5, 10, 40 mm Hg, cardiac index (CI) at every level of PEEP and after IVE at the highest PEEP. Stepwise increases in PEEP (from 0-20 cm H2O) were associated with progressive fall in CI whereas heart rate remained unchanged. Transmural right atrial and PA pressures did not change; transmural LV end-diastolic and systemic arterial pressures and peak dP/dt decreased significantly with PEEP, except for dT/dt/dPt. IVE reversed this fall in CI and peak dP/dt. Whereas transmural LV end-diastolic pressure rose markedly. We conclude that the observed fall in LV performance during PEEP is not the result of a depressed LV contractility because PEEP does not induce a decrease in dP/dt/DPt, the least sensitive to change in preload isovolumic phase indices of contractility.