Transpulmonary pressure gradient verifies pulmonary hypertension is initiated by increased arterial resistance in broilers.

Previous hemodynamic evaluations demonstrated that pulmonary arterial pressure (PAP) is higher in broilers that are susceptible to pulmonary hypertension syndrome (PHS, ascites) than in broilers that are resistant to PHS. We compared key pulmonary hemodynamic parameters in broilers from PHS-susceptible and PHS-resistant lines (selected for 12 generations under hypobaric hypoxia) and in broilers from a relaxed (control) line. In experiment 1 the PAP was measured in male broilers in which a flow probe positioned on one pulmonary artery permitted the determination of cardiac output and pulmonary vascular resistance (PVR). The PAP and relative PVR were higher in susceptible broilers than in relaxed and resistant broilers, whereas absolute and relative cardiac output did not differ between lines. In experiment 2 male and female broilers from the 3 lines were catheterized to measure pressures in the wing vein, right atrium, right ventricle, pulmonary artery, and pulmonary veins (WP, wedge pressure). The transpulmonary pressure gradient (TPG) was calculated as (PAP-WP), with PAP quantifying precapillary pressure and WP approximating postcapillary pulmonary venous pressure. When compared with resistant and relaxed broilers, PAP values in susceptible broilers were > or =10 mmHg higher, TPG values were > or =8 mmHg higher, and WP values were < or =2 mmHg higher, regardless of sex. The combined hemodynamic criteria (elevated PAP and PVR combined with a proportionally elevated TPG) demonstrate that susceptibility to PHS can be attributed primarily to pulmonary arterial hypertension associated with increased precapillary (arteriole) resistance rather than to pulmonary venous hypertension caused by elevated postcapillary (venous and left atrial) resistance.