Table 1.

Calculations for derived measures.

Measure	Calculation
PVR	$\frac{(\mathrm{PAP}-\mathrm{LAP})}{\mathrm{PBF}}$
AaDO2	$\left[\mathrm{Fi}{\mathrm{O}}_2\times ({\mathrm{P}}_{\mathrm{atm}}-{\mathrm{P}}_{{\mathrm{H}}_2\mathrm{O}})-\frac{\mathrm{PaC}{\mathrm{O}}_2}{\mathrm{RQ}}\right]-\mathrm{Pa}{\mathrm{O}}_2$

PVR, pulmonary vascular resistance; PAP, pulmonary artery pressure (mmHg); LAP, left atrial pressure, assumed to equal 9 mmHg based on previous studies (22); PBF, pulmonary blood flow (ml/min); AaDO₂, alveolar-arterial difference in oxygen; FiO₂, fraction of inspired oxygen (%); P_atm, atmospheric pressure (760 mmHg); P_H2O, water vapor pressure at body temperature (47 mmHg at 39°C); PaCO₂, partial pressure of carbon dioxide (mmHg); RQ, respiratory quotient (0.8); PaO₂, partial pressure of oxygen (mmHg).