Effects of Spinal Segmental Afferents on Intercostal Muscles Activity during High Frequency Spinal Cord Stimulation (HF-SCS)

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. Objective: To examine the effects of spinal segmental afferents on1) inspiratory intercostal muscle activation during loaded breathing and 2) post-inspiratory activity following HF-SCS. Methods: In 6 anesthetized and C2 spinalized dogs, a laminectomy was performed over the thoracic spine from the T1 to T5 levels. A stimulating disc electrode was positioned on the ventral surface of the spinal cord at the T2 level. Recording electrodes were placed in the parasternal (PA) and external (EI) intercostal muscles (2 nd and 3 rd interspaces respectively) to record multiunit EMG activity. During HF-SCS inspiratory intercostal muscle activity was assessed before and after bilateral dorsal rhizotomy (from T1-T5) following single 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 174±6% of that observed during control breaths (p<0.01) whereas PA activity was unchanged (105±2%; NS). Following dorsal rhizotomy, facilitation of EI activity was significantly reduced (121±4%, p<0.05), and PA activity was unchanged (99±2%, NS). Under control conditions, there was significant post-inspiratory activity in the EI but only minimal activity in the PA. Following dorsal rhizotomy, post-inspiratory activity was absent. Summary: Similar to observations in spontaneously breathing animals, these results, demonstrate that during HF-SCS in C2 spinalized dogs: 1) airway occlusion results in compensatory increases in EI muscle activation, but not PA and 2) afferent inputs from muscle receptors, presumably muscle spindles, are a primary determinant of post-inspiratory EI activity. Conclusion: 1)Airway obstruction, duringHF-SCS to support ventilation in tetraplegic patients, may elicit compensatory increases in EI but not PA muscle activation and 2) post-inspiratory activity is mediated primarily by spinal afferents. National Institutes of Health grant no. R01 NS105785. This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.