RELATIONSHIPS BETWEEN REGIONAL VENTILATION AND VASCULAR AND EXTRAVASCULAR VOLUME IN SUPINE HUMANS

With the use of positron emission tomography, alveolar ventilation (VA), lung density, and pulmonary blood volume (V-B) were measured regionally in eight nonsmokers in the supine posture and one nonsmoker in the prone posture during quiet breathing in a transaxial thoracic section at midheart level. Regional values of alveolar volume (V-A) and extravascular tissue volume (V-EV) were derived from the inherent relationships between different compartments in the lung. Ratios proportional to gas volume (V-A/V-EV) and ventilation (VA/V-EV) per alveolar unit, respectively, were calculated. No differences between right acid left lung were found. Variations in the vertical direction could explain similar to 65% of the total within-group variation in V-A, V-B, and In (VA), whereas the corresponding value for horizontal variation was only 3-9% (right lung, supine subjects). Similar gravitational gradients were found in the single prone subject. There was a significant linear correlation between V-A and In (VA). When V-A and VA are related to a given number of alveolar units (V-EV), the data are consistent with a linear relationship between VA/V-EV and V-A/V-EV, indicating that ventilation might be explained by the elastic properties of lung tissue according to Salazar and Knowles (J. Appl. Physiol. 19: 97-104, 1964). Regional V-B was closely associated with the gradient of regional alveolar volume (V-A/V-EV) (by virtue of weight of blood and competition for space) and therefore, indirectly, closely associated with the vertical gradient of ventilation.