Local regulation of pulmonary blood flow and ventilation perfusion ratios in the coatimundi

Small catheters (ca. 3 mm diameter at tip) were wedged in subsegmental bronchi in anesthetized coatimundi (Nasua nasua) during spontaneous breathing. Mixed expired gases of a group of lobules were sampled continuously without contamination from neighboring units, and local tidal volume, frequency, carbon dioxide production, and oxygen consumption were measured, as well as mixed venous PO₂ and PCO₂. Local ventilation perfusion ratio, alveolar PO₂, PCO₂, and blood flow were calculated. There was a 22% reduction (range 15 to 38) in local perfusion (as percent of flow at PAO₂, 100 mmHg) per 10 mmHg fall in local alveolar oxygen tension over the PAO₂ range 150-36 mmHg. Local hypercapnia had little effect on local flow. Local tidal volume (ca 1% of total tidal volume) was unaffected by changes in alveolar gas tensions. The contribution of vasoconstriction or vasodilatation, as a negative feedback system, to the stability of local PAO₂ was greatest close to the physiologic range (65 to 85 mmHg) falling off outside these values, but at best the system had only a moderate efficiency.