Simulation of acute spinal cord injury: effects on respiration

The respiratory effects of acute spinal injury and paralysis are difficult to study. Urgent medical needs of human spinal cord injury victims usually preclude study, while induction of spinal cord lesions in awake animals is not feasible ethically. We utilized controlled, segmental infusion of epidural anesthetic in awake, highly trained, implanted canines to reversibly simulate the effects of thoracic and cervical (paraplegic and quadriplegic) spinal cord injury. We studied six animals, an average of 29 days after implantation with electromyogram and sonomicrometry transducers in transversus abdominis, external intercostal, parasternal intercostal and costal diaphragm muscles. Anesthetic was infused through an epidural catheter inserted percutaneously, under fluoroscopic guidance. Asymmetrical motor blockade was prevented using repositioning during epidural infusions. By sequential infusion we were able to induce three distinct, functional levels of spinal paralysis showing cumulative paralysis of abdominal, external intercostal, and parasternal intercostal muscles. Paralysis of the abdomen and chest wall, sparing only the diaphragm, showed unexpected bradypnea and failure to maintain minute ventilation.