eFigure 25-10.

Face-on views of freeze-dried, stained alveolar walls (200-µm-thick section) showing the distribution of the pulmonary capillary bed in anesthetized cats.

A, Zone I lobe. B, Zone II lobe. C, Zone III lobe. Morphometric analysis showed that 21% of the alveolar walls were occupied by red blood cells in zone I lobes, 43% in zone II lobes, and 61% in zone III lobes. Independent changes in pulmonary arterial or venous pressure were associated with changes in the pulmonary capillary blood volume over a threefold range.

(From Vriem CE, Staub NC: Pulmonary vascular pressures and capillary blood volume changes in anesthetized cats. J Appl Physiol 36:275–279, 1974.)