Pulmonary wedge pressures confirm pulmonary hypertension in broilers is initiated by an excessive pulmonary arterial (precapillary) resistance

High retrograde pressure through the pulmonary venous system caused by fail ure of the left ventricle or left atrio-ventricular valve may result in the elevated pulmonary arterial pressure and right ventricular hypertrophy ass ociated with pulmonary hypertension syndrome (PHS; ascites) in broiler chic kens. In the present study, unanaesthetized male broilers from an ascites-r esistant line, the base population from which the resistant line was derive d, and a separate unselected line were used to determine whether changes in wedge pressure (thought to be similar to left atrial pressure) are predict ive of differences in the pulmonary arterial pressure of clinically healthy and pre-ascitic broilers. Venous, right atrial, right ventricular, pulmona ry arterial, and wedge pressures were obtained by inserting a catheter into a wing vein and progressively advancing the catheter into a pulmonary bran ch artery until the catheter tip became wedged in and occluded the flow thr ough a terminal artery. Mean right ventricular and pulmonary arterial press ures were lower in the resistant line than in the base population, but wedg e pressures did not differ between the resistant, base, and unselected line s. Right:total ventricular weight ratios (RV:TV) and the percentage saturat ion of hemoglobin with oxygen in arterial blood ranged in value from 0.18 t o 0.44 and 65 to 96%, respectively. Wedge pressure, however, remained simil ar when preascitic broilers with high RV:TV Values and low oximetry values were compared with clinically healthy broilers. In all birds, whether healt hy or showing pre-ascitic characteristics, the wedge pressure was slightly higher than the right atrial pressure but substantially lower than pulmonar y arterial pressure. These observations provide definitive proof that pulmo nary hypertension is initiated as a consequence of excessive pulmonary arte rial or arteriole resistance. Pulmonary venous pressure is estimated by mea suring the pulmonary arterial wedge pressure, and high wedge pressures woul d be evident if pulmonary hypertension was caused by the elevated downstrea m resistances associated with left-sided heart failure.