Effects of lateral recumbency on regional lung function in anesthetized horses

Six horses were anesthetized and placed in lateral recumbency for 1 hour and then were turned to the opposite side for an additional hour. A short-lived radioactive gas, 81mKr, was used to determine the relative spatial distribution of ventilation (V) and perfusion (Q) in these horses. Effects of time, side down, and turning on the distribution were evaluated. A consistent gradient of V/Q was found at all times, with the highest V/Q values at the top (non-dependent) portion of the lung field and the lowest at the bottom (dependent). This gradient was also present within each lung, as well as between lungs. Effects of time were not observed. Horses starting in right lateral recumbency had larger gradients of V/Q than did those starting on the left. The gradient decreased after turning in both groups. After turning, the gradients in the right lung were again greater han those in the left lung.