Pulmonary capillary length in dog, cat and rabbit

Abstract

We perfused isolated, air-filled lungs of dog, cat and rabbit via the pulmonary artery with whole blood followed by olive oil stained black. The oil did not pass into the capillary bed so that the arteries were black and the veins red. We rapidly froze the lungs and on random samples we measured the average minimal capillary path between arterioles (less than 60 μ diameter) and venules (less than 60 μ diameter) both on the lung surface and in the interior in different planes. The average length of pulmonary capillaries is 600–800 μ in dog and cat and 550–650 μ in rabbit. On the average each capillary is continued over 5 to 7 different alveoli. Using available data on red cell velocity in capillaries at the pleural surface in closed-thorax, anesthetized animals we calculated the average transit time (contact time) of red cells with alveolar gas to be 0.35 to 1.7 sec (average 0.8 sec). This is essentially the same as determined by the indirect measurement of pulmonary capillary blood volume by carbon monoxide methods. There is thus adequate time of oxygen diffusion and reaction with hemoglobin to reach completion.