PEEP-induced pulmonary vasoconstriction in neonatal piglets: analysis by pressure-flow curves

We analyzed the effect of two levels of positive end-expiratory pressure (PEEP: 10 and 15 cm H2O) on pulmonary hemodynamics in neonatal piglet lungs isolated in situ and perfused extracorporeally using pulmonary artery pressure-flow (Pa/Q) relationships. Pulmonary artery pressure (Pa) was measured at flow rates of 50, 75, 100, 125, and 150 mL/kg/min. Pa/Q relationship was evaluated by the slope of the Pa/Q plot and the zero-flow intercept pressure (Pi). Pa/Q relationship with PEEP was studied before and after verapamil. Both levels of PEEP increased the slope of the Pa/Q plot and Pi. PEEP of 15 cm H2O resulted in a steeper slope and a higher Pi compared to 10 cm H2O of PEEP (P < 0.05). Verapamil abolished the increase in slope of the pulmonary artery Pa/Q plot but did not affect the increase in Pi with PEEP. The increase in Pi was equal to the increase in mean airway pressure. Verapamil did not affect changes in ventilatory parameters. PEEP increased pulmonary vascular resistance (PVR) both by increasing the Pi, which reflects the weighted average of the critical closing pressure, and represents a "Starling resistor" phenomenon, and an increase in the slope of the P-Q plot, reflecting an increase in pulmonary vascular tone. This response may be unique to the neonatal pulmonary circulation.