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Despite clinically available methods of diaphragm pacing, most patients with ventilator-dependent tetraplegia are still dependent on mechanical ventilation. Given the significant disadvantages of these devices, additional pacing options are needed. The objective of this study was to evaluate a novel and potentially more physiological method of inspiratory muscle activation, which involves the application of high-frequency (>200 Hz) stimulation to the ventral surface of the spinal cord in the high thoracic region. Studies were performed in 13 anesthetized dogs. High-frequency spinal cord stimulation (HF-SCS) results in the activation of both the diaphragm and inspiratory intercostal muscles, in concert, at physiological firing frequencies and the generation of large inspired volumes. Mean maximum firing frequencies of motor units in the parasternal (2nd interspace), the external intercostal (3rd interspace), and the diaphragm muscles were 10.6 +/- 0.4, 11.7 +/- 0.4, and 10.4 +/- 0.3 Hz, respectively. These values were not significantly different from those occurring during spontaneous breathing at comparable inspired volumes. Maximum inspired volume was 0.93 +/- 0.01 liter, which approximates the inspiratory capacity of these animals. Moreover, ventilation can be maintained on a chronic basis by this method (6 h) without evidence of system fatigue. Our results suggest that HF-SCS results in activation of spinal cord tracts that synapse with the inspiratory motoneuron pools, allowing processing of the stimulus and consequent physiological activation of the inspiratory muscles. HF-SCS has the potential to provide an effective method of inspiratory muscle pacing.

Objective-To evaluate the clinical effects of spinal cord stimulation (SCS) to restore cough in subjects with cervical spinal cord injury.Design-Clinical trial assessing the clinical outcomes and side effects associated with the cough system. Setting-Out-patient hospital or residenceParticipants-Subjects (N = 9; 8 men, 1 woman) with cervical spinal cord injury Disclosure: We certify that we have affiliations with or financial involvement (eg, employment, consultancies, honoraria, stock ownership or options, expert testimony, grants and patents received or pending, royalties) with an organization or entity with a financial interest in, or financial conflict with, the subject matter or materials discussed in the manuscript and all such affiliations and involvements are disclosed on the title page of the manuscript. Intervention(s)-SCS was performed at home by either the subjects themselves or caregivers on a chronic basis and as needed for secretion management. Explanation ofMain Outcome Measure(s)-Ease in raising secretions, requirement for trained caregiver support related to secretion management and incidence of acute respiratory tract infections.Results-The degree of difficulty in raising secretions improved markedly, and the need for alternative methods of secretion removal was virtually eliminated. Subject life quality related to respiratory care improved with subjects reporting greater control of breathing problems and enhanced mobility. The incidence of acute respiratory tract infections fell from 2.0 ± 0.5 to 0.7 ± 0.4 events/ subject year (p < 0.01), and mean level of trained caregiver support related to secretion management measured over a 2 week period decreased from 16.9 ± 7.9 to 2.1 ± 1.6 and 0.4 ± 0.3 times/week (p < 0.01) at 28 and 40 weeks following implantation of the device, respectively. Three subjects developed mild hemodynamic effects which abated completely with continued SCS. Subjects experienced mild leg jerks during SCS, which were well tolerated. There were no instances of bowel or bladder leakage.Conclusion(s)-Restoration of cough via SCS is safe and efficacious. This method improves life quality and has the potential to reduce the morbidity and mortality associated with recurrent respiratory tract infections in this patient population.

In patients with ventilator-dependent tetraplegia, phrenic nerve pacing (PNP) provides significant clinical advantages compared with mechanical ventilation. This technique however generally requires a thoracotomy with its associated risks and in-patient hospital stay and carries some risk of phrenic nerve injury. We have developed a method by which the phrenic nerves can be activated via intramuscular diaphragm electrodes. In one patient with ventilator-dependent tetraplegia, two intramuscular diaphragm electrodes were implanted into each hemidiaphragm near the phrenic nerve motor points via laparoscopic surgery. The motor points were identified employing a previously devised mapping technique. Because inspired volumes were suboptimal on the right, a second laparoscopic procedure was necessary to position electrodes near the anterior and posterior branches of the right phrenic nerve. During bilateral stimulation, inspired volume was 580 ml. After a reconditioning program of progressively increasing diaphragm pacing, maximum inspired volumes on the left and right hemidiaphragms increased significantly. Maximum combined bilateral stimulation was 1120 ml. Importantly, the patient has been able to comfortably tolerate full-time pacing. If confirmed in additional patients, PNP with intramuscular diaphragm electrodes via laparoscopic surgery may provide a less invasive and less costly alternative to conventional PNP.