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 of these muscles, we first measured the changes in gastric pressure (Delta Pga) during paired bilateral stimulation of the lower thoracic nerve roots in eight chronic patients with C5-C7 tetraplegia and eight matched unaffected subjects in the seated posture. Stimulations were applied with a 90-mm circular magnetic coil positioned at the level of T10 and connected to a Magstim 250 stimulator. During relaxation at FRC, Delta Pga during maximal stimulation 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). Stimulations were next applied during the course of a forced expiration. All patients consistently demonstrated an abrupt increase in esophageal pressure (22.7 +/- 4.5 cm H2O), and six of them also showed an increase in expiratory flow. The cumulative thickness of the four abdominal muscles, as measured with an ultrasound probe, was 34% smaller in the patients than in the control 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 abdominal muscles elicits increases in intrathoracic pressure that are greater than those required to initiate dynamic airway compression; it might, therefore, improve the clearing of airway secretions.