Pulmonary arteriovenous anastomoses in the avian lung: do they exist?

Study of Stress Induced Failure of the Blood-gas Barrier and the Epithelial-epithelial Cells Connections of the Lung of the Domestic Fowl, Gallus gallus Variant Domesticus after Vascular Perfusion

Complete blood-gas barrier breaks (BGBBs) and epithelial-epithelial cells connections breaks (E-ECCBs) were enumerated in the lungs of free range chickens, Gallus gallus variant domesticus after vascular perfusion at different pressures. The E-ECCBs surpassed the BGBBs by a factor of ~2. This showed that the former parts of the gas exchange tissue were structurally weaker or more vulnerable to failure than the latter. The differences in the numbers of BGBBs and E-ECCBs in the different regions of the lung supplied with blood by the 4 main branches of the pulmonary artery (PA) corresponded with the diameters of the blood vessels, the angles at which they bifurcated from the PA, and the positions along the PA where they branched off. Most of the BGBBs and the E-ECCBs occurred in the regions supplied by the accessory- and the caudomedial branches: the former is the narrowest branch and the first blood vessel to separate from the PA while the latter is the most direct extension of the PA and is the widest. The E-ECCBs appeared to separate and fail from tensing of the blood capillary walls, as the perfusion- and intramural pressures increased. Compared to the mammalian lungs on which data are available, i.e., those of the rabbit, the dog, and the horse, the blood-gas barrier of the lung of free range chickens appears to be substantially stronger for its thinness.

Structural failures of the blood-gas barrier and the epithelial-epithelial cell connections in the different vascular regions of the lung of the domestic fowl, Gallus gallus variant domesticus, at rest and during exercise

Structural failure of blood–gas barrier (BGB) and epithelial–epithelial cell connections (EECCs) in different vascular regions of the exchange tissue of the lung was studied in rested and exercised chickens. The number of red blood cells (nRBCs) was counted and protein concentration (PC) measured after lavaging the respiratory system, and blood was sampled to determine the blood lactate levels (BLLs). The numbers of complete BGB breaks (nBGBBs) and those of the EECCs (nEECCBs) were counted in the different vascular territories of the lung. The nRBCs and the PCs increased with increasing exercise intensities but the rate of increase decreased at higher workloads. From rest to the fastest experimental treadmill speed of 2.95 m.sec⁻¹, BLLs increased 4-fold. In all cases, the nEECCBs exceeded those of the BGB, showing that structurally the BGB is relatively weaker than the EECC. The increase in the number of breaks with increasing exercise can be attributed to increase in the pulmonary capillary blood pressure (PCBP) from faster heart rates and higher cardiac outputs, while the leveling out of the measurements made at higher workloads may have arisen from hemodynamic changes that initially ensued from exudation of blood plasma and then flow of blood into the air capillaries on failure of the BGB. The relative differences in the nBGBBs and the nEECCBs in the different vascular regions of the lung were ascribed to diameters of the branches and their points of origin and angles of bifurcation from the pulmonary artery. Presence of RBCs in the air capillaries of the lungs of rested chickens showed that failure of the BGB commonly occurs even in healthy and unstressed birds. Rapid repair and/or defense responses, which were observed, may explain how birds cope with mechanical injuries of the BGB.

Control of respiration in the chicken: effects of venous CO2 loading

To determine if ventilation in unanesthetized chickens is adjusted sufficiently to prevent alterations in the partial pressure of carbon dioxide in arterial blood (PaCO2) when the CO2 content of mixed venous blood is changed, hypercapnic (PCO2 about 533 Torr) and hypocapnic (PCO2 less than 10 Torr) blood was infused into the left jugular vein of decerebrate chickens at 38 ml . min-1 for 30 sec. Ventilation and PaCO2 were assessed by determining respiratory frequency (f), tidal volume (VT), and the end-tidal CO2 fraction while serial samples of arterial blood were withdrawn from the sciatic artery. Infusion of hypercapnic blood resulted in an increase VT and minute ventilation (VE) as well as an increase in PaCO2. Infusion of hypocapnic blood resulted in a decrease in VT and VE and a small, transient decrease in PaCO2; the PaCO2 often returned to control levels before the end of the infusion period. The respiratory control system in the chicken appears to be better able to maintain a constant PaCO2 when perturbed by a reduced venous CO2 load reaching the lung than when perturbed by a reduced venous CO2 load reaching the lung than when perturbed by an increased CO2 load. These results are consistent with the hypothesis that intrapulmonary CO2 receptors, whose sensitivity to PCO2 is highest at low PCO2, are involved in the breath-to-breath control of breathing in birds.

Observations on the avian pulmonary and bronchial circulation using labelled microspheres

Domestic fowl, ducks, geese, Guinea-fowl, quail and pigeons were anaesthetised with intravenous pentabarbitone sodium. Carbonised microspheres (40,000-60,000), 15 micrometer +/- 5 micrometer in diameter and labelled with 85Sr (3M Company) were injected into the cannulated right atrium. After spontaneous breathing of room air the birds were killed and the radioactivity measured in the spleen, kidneys, brain, lungs and extrapulmonary primary bronchi. Small pieces of lung tissue were removed from the beginning (costal region), middle (costovertebral region), and the end (vertebral region) of the paleopulmonic parabronchi, in the direction of air flow. Microspheres found in samples of parabronchial tissue indicated the relative perfusion rates of the three regions. Thermal panting was induced in six domestic fowl and six pigeons, followed by injection of microspheres. No arteriovenous anastomoses were found to exist across the pulmonary bed in any of the species examined at rest or in the panting domestic fowl and pigeons. The extrapulmonary primary bronchus was found to be well perfused from the pulmonary artery in the domestic fowl and to a lesser extent in the other species. The perfusion of the parabronchi in the domestic fowl and pigeons at rest decreased in the direction of ventilatory gas flow. This blood flow gradient was significantly increased during thermal panting in the domestic fowl, but not in the pigeon.