Pattern of Inspiratory Intercostal Muscle Activation during High Frequency Spinal Cord Stimulation (HF‐SCS)

Abstract

ObjectiveHF‐SCS is a novel technique of inspiratory muscle activation involving spinal cord pathways. The purpose of the present study was to compare the distribution of motor drive to the intercostal muscles during spontaneous breathing with that occurring during HF‐SCS.MethodsIn 4 anesthetized dogs, electrical stimulation was applied via a stimulating electrode on the ventral surface of the upper thoracic spinal cord at the T2 level. Fine wire recording electrodes were used to assess single motor unit (SMU) pattern of activation of the parasternal (PA, 2nd interspace) and external [dorsal portions of the 3rd (EI‐3D) and 5th (EI‐5D) and ventral portion of the 3rd (EI‐3V) interspaces] intercostal muscles.ResultsMean maximum discharge frequency of PA was 10.6±0.3 Hz. Mean maximum discharge frequency of EI‐3D (13.7±0.5Hz) was significantly greater than that of the EI‐3V (8.8±0.3Hz) and the EI‐5D (9.9±0.3Hz) (p<0.05). Importantly, these values were not significantly different than those occurring in the same animals during spontaneous breathing.ConclusionThis study demonstrates that HF‐SCS results in the same differential pattern of activation of the various intercostal muscles as that which occurs during spontaneous breathing. Moreover, the neural circuitry resulting in physiologic activation of the rib cage muscles exists within the spinal cord.Support: NIH‐NINDS (R01NS064157)