Model ft03

Randomly selected rats from normoxia and 48-hr hyperoxia WT and KO groups were anesthetized with pentobarbital sodium (50–100 mg/kg i.p.). The lungs were then removed and suspended from a calibrated force displacement transducer (ModelFT03; Grass Instruments), attached to a rat lung ventilation-perfusion system, and lung weight was monitored continuously (26 (link), 31 (link)). The value of K_f, a measure of vascular permeability, was then determined using the approach described by Bongard et al. (31 (link)). Briefly, after a 10 min stabilization period with the venous pressure (P_V) set at atmospheric pressure, P_V was raised to 3.7 mmHg and the lung perfused for 10 min. Then, P_V was raised to 10 mmHg and perfusion continued for an additional 10 min. K_f was determined by dividing the difference in the rate of lung weight gain measured 10 min after increasing P_V from 3.7 to 10 mmHg and after increasing P_V from 0 to 3.7 mmHg by the difference in pulmonary capillary pressure at these P_V values. For each P_V, the capillary pressure was estimated as the average of arterial and venous pressures. K_f was normalized to gram of dry lung weight.

The heart and lungs from an independent group of rats were isolated at the 2 week time point and suspended from a calibrated force displacement transducer (ModelFT03; Grass Instruments) and lung weight was monitored continuously as described (21 (link)). The lungs were perfused and ventilated (40 breaths/min) with end-inspiratory and end-expiratory pressures of ~ 8 and 4 cm H₂O. The K_f was determined using the approach described by Bongard et al. (22 (link)). The venous pressure (P_V) was set at atmospheric pressure then raised to 5 cm H₂O for 10 min and 13.5 cm H₂O for an additional 10 min. At the end, the lungs were removed from the perfusion system, the arterial and venous cannulas connected, and pressure drop in the cannulas (ΔP_can) was determined. The pulmonary vascular pressure, R_V, was then calculated using
$$R_v=\frac{P_a-\mathrm{\Delta }{P}_{\mathit{can}}}{F}$$ where P_a is the pulmonary arterial pressure measured at the end of the 10-min stabilization period with P_v set at 0 mmHg, and F is the pump flow rate (0.03 ml/min/g body wt).