Adjustment of the Regional Pulmonary Circulation to the Profile of Oxygen Pressure Along the Parabronchus in the Duck

Summary

Radioactively labeled microspheres were used in the duck in order to study the distribution of pulmonary blood flow. In the awake, spontaneously breathing animal, blood flow to the parabronchial gas exchange tissue decreased in the same direction as gas flows through, and thus as ${\text{P}}_{{\text{O}}_{\text{2}} }$ decreased along, the parabronchi. Hypoxia could be shown to exert a vasoconstriction in the lung of the duck and thus provides a potential mechanism for the blood flow pattern in the awake duck. However, when the direction of parabronchial gas flow was artificially reversed, the pattern of perfusion did change only slightly, suggesting that the ${\text{P}}_{{\text{O}}_{\text{2}} }$ profile is not the main determinant of the perfusion profile within the parabronchi of the spontaneously breathing animals. It can be shown in theory that any inhomogeneity of lung perfusion in birds results in a reduction of the gas exchange efficiency. However, at the level of inhomogeneity observed in this study the impairment is expected to be insignificant.