Patients with complete spinal cord injury above the phrenic motor nucleus need full ventilatory support to survive. As an alternative to external ventilators, implanted phrenic nerve 'pacemakers' have been available for more than 30 years (Glenn, 1980). However, these have potential problems, including synchronous activation of motor units and reversal of the normal recruitment order.Recently DiMarco &Kowalski (2009,2010) performed proof-of-principle experiments to overcome these difficulties. They applied high-frequency electrical stimulation (50-300 s"1) to the T2 spinal cord in anaesthetised dogs, acutely spinalised at C2. The stimulation was applied in bursts to simulate inspiration and it activated widely spaced inspiratory motoneurone pools (diaphragm, intercostal and scalene muscles) in a remarkably physiological manner. Motoneurones were activated asynchronously, as in normal breathing, and the resulting contractions maintained ventilation for several hours.
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