(763.2) Evaluation of Loaded Breathing on Inspiratory Intercostal Muscle Activation During High Frequency Spinal Cord Stimulation to Restore Breathing in Spinal Cord Injury – Animal Model

Poster Board Number: E542

Krzysztof Kowalski (MetroHealth System and Case Western Reserve University), Anthony DiMarco (MetroHealth System and Case Western Reserve University)

Background: High Frequency Spinal Cord Stimulation (HF-SCS) is a unique method of inspiratory muscle activation and has the potential to restore breathing in ventilator dependent tetraplegic subjects.  However, these subjects are 3-4 times more likely to have sleep disordered breathing (SDB) and have a higher incidence of obstructive airways disease than individuals in the general population, resulting in an increased inspiratory load. 

Objective: To examine the effects of increased inspiratory load (airway occlusion) on inspiratory intercostal muscle activation during HF-SCS.

Methods: In 3 spinalized (C2 level) anesthetized dogs, recording electrodes were positioned in the parasternal (PA) and external (EI) intercostal muscles (2nd and 3rd interspaces respectively) to record multiunit (integrated) and single motor units (SMU) EMG activities. During HF-SCS at functional residual capacity (FRC), respiratory muscle activity was assessed before and after single and multi-breath airway occlusion. 

Results: During HF-SCS, tracheal occlusion resulted in augmentation of peak multi-unit integrated EI, but little change in PA EMG activity. During the occluded breath, EI activity increased to 148 ± 3% of that observed during control breaths (plt;0.01) whereas PA activity was little changed (105 ± 5%; NS). EI instantaneous SMU peak firing frequency (PFF) was also greater during the occluded breath (15.7 ± 1.6Hz vs. 11.3 ± 0.3Hz; plt;0.05). whereas there was only a small increase in PA PFF (10.8 ± 0.6Hz vs. 10.0 ± 0.6Hz; NS).

Summary: HF-SCS during airway occlusion results in significant increases in activation of the EI but not PA muscles.

Conclusion: HF-SCS applied to support ventilation in high tetraplegics with airway obstruction may elicit compensatory increases in EI muscle activation.  These results support the concept that spinal reflex effects remain functional during HF-SCS. The EI have a much higher density of muscle spindles compared to the PA muscles, which may mediate the differential activation of these muscles.

lt;bgt;Support:lt;/bgt; National Institutes of Health grant no. R01 NS105785.

lt;b style="font-size: 1em;"gt;Conflict of interest: lt;/bgt; Drlt;b style="font-size: 1em;"gt;. lt;/bgt;A. DiMarco is a founder of and has a significant financial interest in Synapse BioMedical, a manufacturer of diaphragm pacing systems and holds patents for spinal cord stimulation to restore cough and respiration (nos. 5,678,535; 5,911,218; 5,999,855; and 8,751,004). Dr. A. DiMarco and Dr. K. Kowalski hold the U.S. patents for technology related to the content of this manuscript, Respiratory Muscle Activation by Spinal Cord Stimulation (no. 8,352,036).