New Paper: Temperature increases by kHz frequency spinal cord stimulation
Zannou, A. L.*, Khadka, N.*, Truong, D. Q., Zhang, T., Esteller, R., Hershey, B., & Bikson, M. 2018. Temperature increases by kilohertz frequency spinal cord stimulation.
Kilohertz frequency spinal cord stimulation (kHz-SCS) deposits significantly more power in tissue compared to SCS at conventional frequencies, reflecting increased duty cycle (pulse compression). We hypothesize kHz-SCS increases local tissue temperature by joule heat, which may influence the clinical outcomes. To establish the role of tissue heating in KHZ-SCS, a decisive first step is to characterize the range of temperature changes expected during conventional and KHZ-SCS protocols. Fiber optic probes quantified temperature increases around an experimental SCS lead in a bath phantom. These data were used to verify a SCS lead heat-transfer model based on joule heat. Temperature increases were then predicted in a seven-compartment (soft tissue, vertebral bone, fat, intervertebral disc, meninges, spinal cord with nerve roots) geometric human spinal cord model under varied parameterization. The experimentally constrained bio-heat model shows SCS waveform power (waveform RMS) determines tissue heating at the spinal cord and surrounding tissues. For example, we predict temperature increased at dorsal spinal cord of 0.18e1.72 ° C during 3.5 mA peak 10 KHz stimulation with a 40-10- 40 ms biphasic pulse pattern, 0.09e0.22 ° C during 3.5 mA 1 KHz 100-100-100 ms stimulation, and less than 0.05 ° C during 3.5 mA 50 Hz 200-100-200 ms stimulation. Notably, peak heating of the spinal cord and other tissues increases superlinearly with stimulation power and so are especially sensitive to in- cremental changes in SCS pulse amplitude or frequency (with associated pulse compression). Further supporting distinct SCS intervention strategies based on heating; the spatial profile of temperature changes is more uniform compared to electric fields, which suggests less sensitivity to lead position. Tissue heating may impact short and long-term outcomes of KHZ-SCS, and even as an adjunct mechanism, suggests distinct strategies for lead position and programming optimization.