Clapping or percussion causes atelectasis in dogs and influences gas exchange

We examined the effects of 10 min of lower lateral chest wall percussion with a mechanical percussor or hand clapping in groups of anesthetized, paralyzed, and ventilated supine dogs. Mechanical percussion was applied at 10-16 Hz and caused an esophageal pressure swing (delta Pes) of 10-17 cmH2O. Hand clapping was applied at 4-7 Hz and caused a delta Pes of 6-17 cmH2O. At necropsy there were large reddened areas on the lateral surface of the underlying lung as well as smaller reddened areas on the hilar surfaces of both lungs and on the lateral surface of the opposite lung. These reddened regions were demonstrated to be atelectatic by postmortem lung inflation (which caused the reddened areas to disappear) and by microscopic examination. Despite the atelectasis, gas exchange improved toward the end of the percussion or clapping period. In four dogs that were ventilated for an additional 20 min after percussion, there was a tendency for gas exchange initially to worsen and then to gradually improve.