Comparison of wire and disc leads to activate the expiratory muscles in dogs

Abstract

Objective: Respiratory complications account for a major cause of morbidity and mortality in subjects with spinal cord injury (SCI) due to paralysis of the expiratory muscles and the consequent inability to generate effective cough. We demonstrated previously that effective cough can be restored in SCI via spinal cord stimulation (SCS) with disc leads positioned on the lower thoracic and upper lumbar spinal cord via laminotomy incisions. In this study, the effectiveness of wire leads, which can be placed using minimally invasive techniques, to activate the expiratory muscles was evaluated.

Design: Animal study.

Setting: Research laboratory.

Animals: Dogs (n = 8).

Interventions: In separate trials, disc and wire leads were inserted onto the dorsal epidural space at the T9, T11, and L1 spinal cord levels. Effects of electrical stimulation with disc, single wire, and two wire leads placed in parallel were compared.

Outcome measures: Airway pressure generation following stimulation with disc and various configurations of wire leads were compared.

Results: Several different configurations of wire leads resulted in airway pressures that were similar to those generated with monopolar stimulation with disc leads (MSDLs). For example, combined monopolar stimulation with parallel wire leads at the T9 + T11 and T9 + L1 levels resulted in airway pressures that were 103.5 ± 6.4 and 101.9 ± 7.0%, respectively, of those achieved with MSDL. Bipolar stimulation with parallel wire leads at T9-T11 and T9-L1 resulted in airway pressures that were 94.2 ± 3.4 and 96.8 ± 5.0%, respectively, of the pressures achieved with MSDL. Other wire configurations were also evaluated, but were generally less effective.

Conclusion: These results suggest that specific configurations of wire leads, which can be placed via minimally invasive techniques, result in comparable activation of the expiratory muscles compared to disc leads and may be a useful technique to restore cough in persons with SCI.

Figure 1

Effects of monopolar SCS (40 V, 50 Hz, 0.2 millisecond) at the T9, T11, and L1 spinal levels alone and combined T9 + T11 and T9 + L1 stimulation on airway pressure development with the disc and wire leads. A schematic of this configuration is placed at the top of this and all subsequent figures. The effect of SCS is shown for one animal in Panel A; mean results are presented in Panel B. P < 0.05 compared to monopolar disc. See text for further explanation.

Figure 2

Mean relationships between stimulus amplitude and airway pressure generation for disc leads during monopolar stimulation (T9 + T11 and T9 + L1) and wire leads during bipolar stimulation (T9–T11 and T9–L1). *P < 0.05 compared to monopolar disc. See text for further explanation.

Figure 3

Mean relationships between stimulus amplitude and airway pressure generation during monopolar stimulation with disc and parallel wire leads. *P < 0.05 compared to monopolar disc. See text for further explanation.

Figure 4

Mean relationships between stimulus amplitude and airway pressure generation during monopolar stimulation with the disc leads (T9 + T11 and T9 + L1) and bipolar stimulation with the parallel wire configuration (T9–T11 and T9–L1). *P < 0.05 compared to monopolar disc. See text for further explanation.

Figure 5

Mean relationships between stimulus amplitude and airway pressure generation during MSDL and the parallel wire Y-connection configuration. *P < 0.05 compared to monopolar disc. See text for further explanation.