THE EFFECT OF ALTERING PULMONARY BLOOD FLOW ON PULMONARY GAS EXCHANGE IN THE TURTLE TRACHEMYS (PSEUDEMYS) SCRIPTA

摘要

In resting reptiles, the P-O2 of pulmonary venous return (PLA(O2); left atrial blood) may be 20 mmHg (1 mmHg=0.1333 kPa) lower than the P-O2 of gas in the lung, This level of P-O2 is considerably higher than that observed in resting mammals and birds and results from ventilation-perfusion (V over dot/Q over dot) heterogeneity, pulmonary diffusion limitation and intrapulmonary shunting. However, the relative contribution of each of these factors is unknown, Many reptiles, particularly chelonians, exhibit an intermittent ventilation pattern where pulmonary blood flow (Q over dot L) increases during the ventilatory periods and, therefore, we hypothesized that V over dot/Q over dot matching would improve with increasing Q over dot L. We applied the multiple inert gas elimination technique in anaesthetized turtles at 22 degrees C, Turtles were continuously ventilated at a rate of 140 mlkg(-1)min(-1), equivalent to the rate of ventilation within a ventilatory period, Trace amounts of six inert gases were infused through the jugular vein, Blood samples from the pulmonary artery and the left atrium and mixed expired gases were collected for analysis, Q over dot L was reduced by a factor of six (low flow) using a vascular occluder placed around the common pulmonary artery or increased by a factor of two (high flow) through bolus injection of adrenaline, V over dot/Q over dot heterogeneity was significantly reduced with increasing pulmonary blood flow (P<0.05). Consistent with these changes, the effective lung-pulmonary artery P-O2 difference (PL(O2)-PLA(O2)) was reduced (P<0.05) from 58+/-1.6 mmHg to 29+/-5 mmHg (means+/-S.E.M.) and PLA(O2) increased significantly (P<0.05) from 88+/-17 mmHg (low flow) to 120+/-14 mmHg (high flow), There was evidence of pulmonary diffusion limitation under all conditions, which was unchanged with increasing blood flow, These findings suggest that increased pulmonary blood flow during a ventilatory period results in both temporal and spatial matching of ventilation and perfusion, without altering pulmonary diffusion limitation. [References: 45]