The effects of abdominal loading on rib cage distortion in premature infants.

The action of the diaphragm in inspiration is to decrease intrathoracic pressure and raise abdominal pressure, which elevates the rib cage. In the supine position, the rise in abdominal pressure is smaller because of the lack of abdominal muscle tone. In premature infants the inward pull of the diaphragm on the very compliant ribs causes inward movement on inspiration (ie, distortion) which is exacerbated by the lack of intercostal muscle activity during rapid eye movement (REM) sleep, their predominant state. We raised abdominal pressure by means of an inflatable cuff in 12 newborn infants (gestation 28 to 40 weeks) to try to improve inspiratory coupling of the rib cage and diaphragm. There was no significant change in minute ventilation, indicating no ventilatory impairment. In all studies in which there was distortion, abdominal loading produced a reduction or abolition of distortion (P less than .01). Abdominal loading may be useful in reducing diaphragmatic activity in premature infants.