Objective. To determine whether elevations in pulmonary vascular pressure i
nduced by mechanical ventilation are more injurious than elevations of pulm
onary vascular pressure of similar magnitude occurring in the absence of me
chanical ventilation.
Design: Prospective comparative laboratory investigation.
Setting. University research laboratory.
Subjects: Male New Zealand white rabbits.
Interventions: Three groups of isolated, perfused rabbit lungs were exposed
to cyclic elevation of pulmonary artery pressures arising from either inte
rmittent positive pressure mechanical ventilation or from pulsatile perfusi
on of lungs held motionless by continuous positive airway pressure. Peak, m
ean, and nadir pulmonary artery pressures and mean airway pressure were mat
ched between groups (35, 27.4 +/- 0.74, and 20.8 +/- 1.5 mm Hg, and 17.7 +/
- 0.22 cm H2O, respectively).
Measurements and Main Results: Lungs exposed to elevated pulmonary artery p
ressures attributable to intermittent positive Pressure mechanical ventilat
ion formed more edema (6.8 +/- 1.3 vs. 1.1 +/- 0.9 g/g of lung), displayed
more perivascular (61 +/- 26 vs. 15 +/- 13 vessels) and alveolar hemorrhage
(76 +/- 11 % vs. 26 +/- 18% of alveoli), and underwent larger fractional d
eclines in static compliance (88 +/- 4.4% vs. 48 +/- 25.1% decline) than lu
ngs exposed to similar peak and mean pulmonary artery pressures in the abse
nce of tidal positive pressure ventilation.
Conclusions: Isolated phasic elevations of pulmonary artery pressure may ca
use less damage than those occurring during intermittent positive pressure
mechanical ventilation, suggesting that cyclic changes in perivascular pres
sure surrounding extra-alveolar vessels may be important in the genesis of
ventilator-induced lung injury.