David Nguyen – Abstract

Neural drive to the diaphragm in cervical spinal cord injury

Nguyen DAT[1,2], Lewis RHC[1,2,3], Boswell-Ruys CL[1,2,3], Hudson AL[1,2], Gandevia SC[1,2,3] and Butler JE[1,2]
1. NeuRA, Sydney, Australia
2. University of New South Wales, Sydney, Australia
3. Prince of Wales Hospital, Sydney, Australia

In people with cervical spinal cord injury (cSCI), inspiratory muscle strength decreases by ~60% compared to able-bodied individuals. Paralysed or weak respiratory muscles in cSCI compromises lung function, increases the incidence of respiratory infections and can cause dyspnoea (1). Reduced muscle strength in cSCI may result in altered neural drive to the inspiratory muscles to maintain ventilation. This study assessed the neural drive to the diaphragm by recording the discharge properties of single motor units from the diaphragm in participants with chronic cSCI (6 males, 48-78 years, C3-C6 injury, AIS A-C) and able-bodied control participants (6 males matched for age and BMI). In each group, 98 and 166 single motor units, respectively, were discriminated from recordings in the costal diaphragm using a monopolar electrode. A linear mixed-effects model analysis showed higher peak discharge frequencies of motor units during quiet breathing in cSCI (17.2 ± 5.0 Hz; mean ± SD) compared to controls (12.4 ± 2.2 Hz) (P < 0.001). There were no significant differences in tidal volume (0.63-0.76 l), inspiratory time (1.62-1.81 s) or mean air flow (0.39-0.42 l/s). Motor unit potentials in cSCI, compared to controls, were larger in amplitude (1.0 ± 0.7 mV and 0.5 ± 0.3 mV, respectively, P = 0.025) and area (1.79 ± 1.56 µV/s and 0.69 ± 0.53 µV/s, respectively, P = 0.016). This study definitively shows an increase in the neural drive to the diaphragm during quiet breathing and indicates that neurogenic changes occur in diaphragm motor units after cSCI.

1. Raab AM, Krebs J, Perret C, Michel F, Hopman MT & Mueller G (2016) Respir Care 61, 1636-1643