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 moderate increase in cardiac output (CO) causes systemic hypoxemia, thereby exposing a pulmonary incapacity to fully oxygenate the additional blood flowing through the pulmonary vasculature. The susceptibility of broiler chickens to hypoxemia was evaluated in lightly anesthetized, clinically healthy, 40- to 49-d-old males. A snare placed around one pulmonary artery permitted acute, reversible shunting of the entire CO through the unobstructed lung. Blood samples were withdrawn from arterial and venous cannulas for blood gas analysis, and a pulse oximeter was used for noninvasive measurements of the percentage saturation of hemoglobin 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 for 12 min, and 101 mm Hg within 5 min after releasing the snare. The percentage saturation of hemoglobin with oxygen before, during, and after tightening the snare averaged, respectively, 96, 91, and 96% for arterial blood, 81, 55, and 78% for venous blood, and 87, 67, and 88% for arterialized capillary beds. Tightening the snare increased the partial 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 data constitute direct evidence that clinically healthy broiler chickens are susceptible to hypoxemia during an acute moderate (approximately twofold) increase in pulmonary blood flow.