Effect of body orientation on regional lung expansion: a computed tomographic approach

TLDR

The Dynamic Spatial Reconstructor (DSR) was employed to image in vivo lung geometry and function, and its accuracy was validated by scanning dog phantoms with known air content, yielding lung density estimates within 7 % and internal consistency of ±3 %. DSR measurements confirmed that changes in total lung air content matched known inflation steps within 7 %, revealed a ventral‑dorsal gradient at functional residual capacity in supine dogs, showed greatest regional change in dependent lung areas, uniform distribution in prone posture, and suggested that mediastinal positioning, rather than gravity alone, governs regional lung air content.

Abstract

The Dynamic Spatial Reconstructor (DSR) was used to study in vivo lung geometry and function. By replacing the lungs of three dogs with potato flakes and ping-pong balls of known air content and scanning these realistic phantoms in the DSR we have estimated accuracy of lung density to be within 7% and have demonstrated a high (+/- 3%) internal consistency (relative density within dogs). Change in total lung air content (y) as calculated from DSR volume imaging of anesthetized dogs matched the known inflation steps (x) to within 7% [range was 1–7% with a mean of 3 +/- 0.5% (SE)]. A gradient of decreasing percent lung air content was measured in the ventral-dorsal direction at functional residual capacity (FRC) in the supine body posture (y = 3.29% air content/cm lung height + 46.48% air content; r = 0.90). Regional lung air content change with lung inflation was greatest in the dependent lung regions. In contrast, regional lung air content at FRC was approximately uniform along the ventral-dorsal direction with the dog in the prone posture and was 66 +/- 0.6% (SE). Ventral-dorsal gradients in lung air content measured within an isogravimetric plane of the dogs in the left or right lateral body posture suggest that regional differences in lung air content cannot be explained solely on the basis of a direct gravitational effect on the lung. Evidence is presented to suggest a possible major role of the intrathoracic position of the mediastinal contents in determining these lung air content distributions.