Steady-state ventilatory responses to expiratory resistive loading in quadriplegics

Patients with quadriplegia have a limited capacity to recruit expiratory muscles and are deprived of respiratory-related feedback from the rib cage and abdominal wall. We wished to evaluate the compensatory strategies available to such patients during expiratory resistive loading (ERL) and to compare their responses with those of normal healthy individuals. In addition, to determine whether the quadriplegic subjects have a blunted sensory appreciation of added ERL, we also compared sensory detection thresholds (delta R50). Steady-state ventilatory responses to ERL (delta R = 12 cm H2O/L/s) were compared in seven quadriplegic patients (level of injury, C6, C7) and six age-matched normal subjects. Highly significant intergroup differences were evident in the extent of prolongation of expiratory time (TE) and total cycle duration (Ttot) during ERL; values of delta TE and delta Ttot in quadriplegics were, on average, 46% of those of normals (p < 0.001). Minute ventilation (VE) was defended to an equal or better extent in quadriplegics. ERL-induced changes in tidal volume, inspiratory duration, mean inspiratory and expiratory flows, and end-expiratory lung volume (EELV) were not significantly different. Average delta R50 in quadriplegics and normals were (mean +/- SD), 1.73 +/- 0.039 cm H2O/L/s and 1.62 +/- 0.4 cm H2O/L/s, respectively (p = ns). Quadriplegics, therefore, despite substantial sensory and motor deficits, defend ventilation and EELV as effectively as normal individuals and show no attenuation in the ability to detect an added expiratory resistance.