NEONATAL PULMONARY VASCULTURE: RECOVERY FROM POSITIVE END—EXPIRATORY PRESSURE (PEEP) IN IMPACT AND ISOLATED LUNGS

Abstract

Unilateral PEEP (UPEEP) reduces ipsilateral pulmonary blood flow (PBF) in the intact (INT) newborn lamb. On cessation of UPEEP, ipsilateral PBF returns slowly to baseline. Intact and isolated lungs of 9 infant lambs were studied to examine the mechanism of this vascular hysteresis. Flow probes were placed on R and L pumonary arteries (PA) of 4 infant lambs. R and L lungs were intubated endobronchially and synchronously ventilated (Siemens-Elena Servo 900C). UPEEP was applied to the L lung for 4 min, abruptly discontinued and recovery of L lung blood flow (LPBF) followed for 4 min (11 trials). LPA was then occluded (LOC) for 4 min using a balloon catheter and recovery of LPBF on deflation followed for 4 min (11 trials). Recovery of PA pressure (P) after stopping PEEP was studied in 5 infant lambs after median sternotomy. Isolated in situ perfused lungs (ISO) were prepared; pulmonary vasculature paralysed; and recovery of PAP on cessation of PEEP studied. In the INT, on cessation of UPEEP, airway and vascular pressures, lung volumes, and RPBF returned to baseline within 10 sec but LPBF recovered slowly. LPBF returned promptly to baseline after balloon deflation and PAP recovered promptly after stopping PEEP in ISO after paralysis of pulmonary vasomotion. These data suggest that lung distension has a direct effect on pulmonary vascular tone in the intact infant lamb.