Chest wall motion in paraplegic subjects.

To assess the isolated effect of an abnormal increase in abdominal compliance on the pattern of chest wall motion during breathing, we have studied seven patients with complete transection of the midthoracic cord (Th4-Th7). Measurements of chest wall motion were obtained with magnetometers, and concentric needle electrodes were used to record the electromyograms of various respiratory muscles. When breathing quietly in the seated posture, all patients had phasic inspiratory activity in both the scalenes and the parasternal intercostals in the cranial interspaces, and the upper and lower rib cage anteroposterior (AP) diameters increased proportionately and in phase. This confirms that the scalenes and the cranial parasternal intercostals are important determinants of the inspiratory expansion of the rib cage in humans. In six of the seven patients, however, the inspiratory increase in abdomen AP diameter was disproportionately larger than the increase in lower rib cage AP diameter. As a result, the tidal breathing loop was displaced to the right of the relaxed thoracoabdominal configuration. Binding the abdomen reduced or suppressed this deformation. These observations thus indicate that an isolated increase in abdominal compliance may cause the chest wall to depart from its relaxed configuration during breathing. This departure probably results from a combination of two factors: (1) a reduction in the rib cage expanding action of the diaphragm, and (2) a decrease in the activation of the rib cage inspiratory muscles relative to the diaphragm.