Low positive end expiratory pressures improve the left ventricular workload versus coronary blood flow relationship

Positive end expiratory pressure (PEEP) has desirable effects on blood oxygenation. Nonetheless, PEEP ventilation has an adverse cardiovascular response which limits its utilization. We have studied the effect of PEEP ventilation on the relationship between coronary flow (CBF) to left ventricular workload. In the closed chest of surgically instrumented dogs, increasing PEEP caused a significant decrease in aortic, left ventricular pressures and aortic flow. The coronary blood flow decreased by 5% for PEEP values of 4 cm of H2O and by 25% for 14 cm of H2O of PEEP. The left ventricular (dP/dt)max was markedly decreased. Following the application of 16 cm H2O of PEEP, the predicted myocardial oxygen consumption using Kreb's equation decreased by 42% of base line values, p less than 0.001. The ratio of CBF to predicted oxygen consumption increased with higher PEEP values, a 84% increment at 16 cm H2O of PEEP relative to zero PEEP (p less than 0.001). Our results suggest that PEEP may have beneficial effects on the relationship between CBF and the predicted myocardial oxygen consumption, and therefore may minimize hypoxic myocardial situations. Further studies that will directly measure the myocardial oxygen consumption are essential before clinical conclusions can be drawn from our results.