EVIDENCE OF A VENTILATION-PERFUSION MISMATCH DURING ACUTE UNILATERAL PULMONARY-ARTERY OCCLUSION IN BROILERS

A ventilation-perfusion (V/Q) mismatch can be diagnosed when a moderat e increase in cardiac output (CO) causes systemic hypoxemia, thereby e xposing a pulmonary incapacity to fully oxygenate the additional blood flowing through the pulmonary vasculature. The susceptibility of broi ler chickens to hypoxemia was evaluated in lightly anesthetized, clini cally healthy, 40- to 49-d-old males. A snare placed around one pulmon ary artery permitted acute, reversible shunting of the entire CO throu gh the unobstructed lung. Blood samples were withdrawn from arterial a nd venous cannulas for blood gas analysis, and a pulse oximeter was us ed for noninvasive measurements of the percentage saturation of hemogl obin with oxygen in arterialized capillary beds. The partial pressure of oxygen in arterial blood averaged 103 mm Hg during control periods, 79 mm Hg (hypoxemia) when the pulmonary artery snare was tightened fo r 12 min, and 101 mm Hg within 5 min after releasing the snare. The pe rcentage saturation of hemoglobin with oxygen before, during, and afte r tightening the snare averaged, respectively, 96, 91, and 96% for art erial blood, 81, 55, and 78% for venous blood, and 87, 67, and 88% for arterialized capillary beds. Tightening the snare increased the parti al pressure of carbon dioxide and the hydrogen ion concentration above control levels in both arterial and venous blood, and these variables returned to control levels upon release of the snare. The combined da ta constitute direct evidence that clinically healthy broiler chickens are susceptible to hypoxemia during an acute moderate (approximately twofold) increase in pulmonary blood flow.