Effects of overground locomotor training on the ventilatory response to volitional treadmill walking in individuals with incomplete spinal cord injury: a pilot study

Abstract

Introduction: Although there has been substantial emphasis on the neuromuscular and cardiovascular adaptations following rehabilitation, pulmonary adaptations in individuals with incomplete SCI (iSCI) in response to locomotor training have been less frequently studied. In healthy individuals, effective transition from rest to work is accomplished by a hyperpneic response, which exhibits an exponential curve with three phases. However, the degree to which our current understanding of exercise hyperpnea can be applied to individuals with iSCI is unknown. The purpose of this case series was to characterize exercise hyperpnea during a rest to constant work rate (CWR) transition before and after 12-15 weeks of overground locomotor training (OLT).

Case presentation: Six subjects with cervical motor incomplete spinal cord injury participated in 12-15 weeks of OLT. Subjects were trained in 90-min sessions twice a week. All training activities were weight-bearing and under volitional control without the assistance of body-weight support harnesses, robotic devices or electrical stimulation. Six minutes of CWR treadmill walking was performed at self-selected pace with cardiorespiratory analysis throughout the tests before and after OLT. Averaged group data for tidal volume, breathing frequency or V_E showed no difference before and after training. V_E variability was decreased by 46.7% after OLT.

Discussion: CWR V_E from rest to work was linear throughout the transition. Following OLT, there was a substantial reduction in V_E variability. Future research should investigate the lack of a phasic ventilatory response to exercise, as well as potential mechanisms of ventilatory variability and its implications for functional performance.

Keywords: Rehabilitation; Trauma.

Figure 1

The ventilatory response in a representative subject without SCI during a constant work rate test at a self-selected walking speed of 3.2 mph. A typical mono-exponential fit with residuals are shown. Fit parameters were as follows: tau=74 s, amplitude=15 l min⁻¹.

Figure 2

The ventilatory response for a subject with miSCI during a constant work rate test at a self-selected walking speed of 1.7 mph, performed before (a) and following (b) ABR. A mono-exponential fit with residuals and parameters are shown. This was the only subject out of six to display a typical ventilatory response.

Figure 3

The ventilatory response for a representative subject with miSCI during a constant work rate test at a self-selected walking speed of 0.5 mph, performed before (a) and following (b) ABR. A linear fit with residuals are shown. Five of the six subjects had an atypical response, where the mono-exponential model could not be used. A linear model was used instead.