Effects of Spinal Cord Section on Inspiratory Pressure Generation During High Frequency Spinal Cord Stimulation (HF‐SCS)

Abstract

ObjectiveHF‐SCS is a novel and more physiologic method of inspiratory muscle activation which involves activation of spinal cord pathways. The specific pathways by which inspiratory motoneurons are activated by this method however are unknown. The aim of the present study was to evaluate the potential role of upper cervical inspiratory neurons on the observed responses.MethodsIn 6 anesthetized and spinalized (C1 level) dogs, HF‐SCS was applied at T2 level. Airway pressure generation (P) was monitored as an index of the degree of inspiratory muscle activation before and following sequential spinal sections at the C4 (to eliminate upper cervical propriospinal neurons) and subsequently the C8 level.ResultsDuring HF‐SCS, P at FRC was 68±6 cmH2O. Sequential bilateral dorsal columns (DC), lateral funiculi (LF) and complete section (CS) at C4, resulted in no significant changes in P (69±5, 67±5 and 65±7 cmH2O respectively, NS). While DC section at C8 resulted in no changes in P (63±5 cmH2O), LF section resulted in significant reduction in P to 18±3 cmH2O (p<0.05). Subsequent CS resulted in no further reduction in P (14±1 cmH2O, NS).ConclusionDuring upper thoracic HF‐SCS, activation of the phrenic motoneuron pools does not involve upper cervical propriospinal inputs. The phrenic motoneuron pools are activated via spinal pathways located bilaterally in the lateral funiculi.Support: NIH‐NINDS (R01NS064157).