The effect of the absence of abdominal muscles on pulmonary function and exercise

In order to determine the long-term sequelae of prune belly syndrome (PBS) and whether the absence of abdominal wall musculature impairs exercise performance we studied nine patients 6 to 31 yr of age with PBS. Conventional spirometry, lung volumes, DLCO, and respiratory muscle strength were measured. A progressive 1-min incremental exercise test was performed on a cycle ergometer, and relative abdominal and chest wall displacements were measured by respiratory inductive plethysmography (RIP). Mean values of TLC, FRC, and RV were 94 +/- 12, 88 +/- 13, and 94 +/- 41%, respectively. Mean values of PEFR, FEV1, and FEF25-75 were 83 +/- 24, 92 +/- 23, and 83 +/- 28%, respectively. Maximal expiratory pressures were significantly reduced in seven of nine patients, with marked reduction in four (>3 SD below the mean). Percent predicted maximal VO2 achieved, % maximal work, and % maximal heart rate were 79 +/- 13, 78 +/- 14, and 87 +/- 2%, respectively. All seven subjects with absent abdominal musculature had paradoxical motion of the abdomen during quiet respiration in the erect or sitting position and while exercising. These subjects had synchronous breathing at rest in the supine position. Although the etiology of the relatively low work rates and VO2 achieved was multifactorial, we speculate that the abdominal paradox in these subjects necessitates abnormally large rib cage displacements during exercise, which may be a significant contributing factor to exercise limitation in some of these subjects.