Fig 1: Measurement of temperature increases in phantom preparation across rates, waveforms (SCS, sinusoidal, square) and conductivities and verification of FEM SCS heat model.

Dark grey box: standard error of the mean; Light grey box: standard deviation; black line: mean of the data, and the dots are the individual ΔT measurements. (A) Schematic of a salt bath experimental set up with an experimental SCS lead in a salt bath heated in a water bath, function generator driving custom isolator energizing to the experimental SCS lead, and optical temperature probe mounted on a micro-manipulator. (B) ΔT measured at a radial direction away from the electrode contact (E4, positive polarity) when applying a 10 KHz Symmetric biphasic pulsed waveform at 5 mA peak in a low conductivity saline bath, and the corresponding FEM heat model. Spatial temperature field decreased with increasing radial distance as predicted with the highest temperature increases (mean ~ 0.5 °C) measured proximal to the lead (1 mm). (C1) For 10 KHz sinusoidal waveform, temperature increases as a function of peak stimulation intensity in varied saline bath conductivities: Green: 0.047 Sm⁻¹; Blue: 0.47 S/m; Red: 1.62 S/m. Experimental (dots) and predicted (broken lines) ΔT significantly increased with stimulation intensity with higher sensitivity in lower conductivity saline baths. (C2) For 10 KHz sinusoidal waveform, ΔT measurement at varied stimulation frequencies (0.1, 1, 5, 10, 20 kHz) and conductivities. Temperature increases were independent of frequency and consistently higher for low saline conductivity (p < 0.01). (D1) ΔT across different waveforms and stimulation intensities (Main Panel: Peak; Inset: RMS matched) with frequency fixed at 10 KHz. (D2) ΔTs for the different waveforms across various frequencies at RMS stimulation intensities (Square, 5 mA; Sinusoidal, 4.95 mA; Symmetric biphasic pulsed, frequency-dependent RMS).