Abdominal muscle strength in patients with tetraplegia

The abdominal muscles are completely paralyzed after traumatic transection of the cervical cord. To assess the residual pressure-generating capacity o f these muscles, we first measured the changes in gastric pressure (Delta P ga) during paired bilateral stimulation of the lower thoracic nerve roots i n eight chronic patients with C5-C7 tetraplegia and eight matched unaffecte d subjects in the seated posture. Stimulations were applied with a 90-mm ci rcular magnetic coil positioned at the level of T10 and connected to a Mags tim 250 stimulator. During relaxation at FRC, Delta Pga during maximal stim ulation averaged (mean +/- SE) 76.0 +/- 11.7 cm H2O in the control subjects , whereas in the patients it was only 29.9 +/- 3.7 cm H2O (p = 0.002). Stim ulations were next applied during the course of a forced expiration. All pa tients consistently demonstrated an abrupt increase in esophageal pressure (22.7 +/- 4.5 cm H2O), and six of them also showed an increase in expirator y flow. The cumulative thickness of the four abdominal muscles, as measured with an ultrasound probe, was 34% smaller in the patients than in the cont rol subjects and correlated positively with maximal Delta Pga. We conclude that in patients with tetraplegia, muscle atrophy causes a marked reduction in abdominal muscle strength. However, magnetic stimulation of the abdomin al muscles elicits increases in intrathoracic pressure that are greater tha n those required to initiate dynamic airway compression; it might, therefor e, improve the clearing of airway secretions.