Department of Biomedical Engineering, The City College of New York, New York, NY, USA.
Department of Psychiatry, Division of Neuropsychiatry and Neuromodulation, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA.
Neuromodulation. 2023 Oct;26(7):1362-1370. doi: 10.1016/j.neurom.2022.07.006. Epub 2022 Aug 25.
High-density (HD) spinal cord stimulation (SCS) delivers higher charge per time by increasing frequency and/or pulse duration, thus increasing stimulation energy. Previously, through phantom studies and computational modeling, we demonstrated that stimulation energy drives spinal tissue heating during kHz SCS. In this study, we predicted temperature increases in the spinal cord by HD SCS, the first step in considering the potential impact of heating on clinical outcomes.
We adapted a high-resolution computer-aided design-derived spinal cord model, both with and without a lead encapsulation layer, and applied bioheat transfer finite element method multiphysics to predict temperature increases during SCS. We simulated HD SCS using a commercial SCS lead (eight contacts) with clinically relevant intensities (voltage-controlled: 0.5-7 V) and electrode configuration (proximal bipolar, distal bipolar, guarded tripolar [+-+], and guarded quadripolar [+--+]). Results were compared with the conventional and 10-kHz SCS (current-controlled).
HD SCS waveform energy (reflecting charge per second) governs joule heating in the spinal tissues, increasing temperature supralinearly with stimulation root mean square. Electrode configuration and tissue properties (an encapsulation layer) influence peak tissue temperature increase-but in a manner distinct for voltage-controlled (HD SCS) compared with current-controlled (conventional/10-kHz SCS) stimulation. Therefore, depending on conditions, HD SCS could produce heating greater than that of 10-kHz SCS. For example, with an encapsulation layer, using guarded tripolar configuration (500-Hz, 250-μs pulse width, 5-V HD SCS), the peak temperature increases were 0.36 °C at the spinal cord and 1.78 °C in the epidural space.
As a direct consequence of the higher charge, HD SCS increases tissue heating; voltage-controlled stimulation introduces special dependencies on electrode configuration and lead encapsulation (reflected in impedance). If validated with an in vivo measurement as a possible mechanism of action of SCS, bioheat models of HD SCS serve as tools for programming optimization.
高密度（HD）脊髓刺激（SCS）通过增加频率和/或脉冲持续时间来提高每时间的电荷量，从而增加刺激能量。先前，通过体模研究和计算建模，我们证明了在 kHz SCS 期间，刺激能量会驱动脊髓组织发热。在这项研究中，我们预测了 HD SCS 引起的脊髓温度升高，这是考虑加热对临床结果潜在影响的第一步。
我们改编了一个高分辨率计算机辅助设计衍生的脊髓模型，同时具有和不具有导联封装层，并应用生物传热有限元法多物理场来预测 SCS 期间的温度升高。我们使用商业 SCS 导联（八个触点）模拟了 HD SCS，该导联具有临床相关的强度（电压控制：0.5-7 V）和电极配置（近端双极、远端双极、保护三极[+-+]和保护四极[+--+]）。结果与传统和 10-kHz SCS（电流控制）进行了比较。
HD SCS 波形能量（反映每秒电荷量）控制脊髓组织中的焦耳加热，刺激均方根与温度呈超线性增加。电极配置和组织特性（封装层）会影响组织温度的峰值增加，但与电流控制（传统/10-kHz SCS）刺激相比，其影响方式不同。因此，根据情况，HD SCS 产生的加热可能比 10-kHz SCS 更大。例如，在封装层的情况下，使用保护三极配置（500-Hz，250-μs 脉冲宽度，5-V HD SCS），脊髓处的峰值温度增加为 0.36°C，硬膜外腔处的温度增加为 1.78°C。
由于更高的电荷量，HD SCS 会增加组织加热；电压控制刺激会对电极配置和导联封装（反映在阻抗中）产生特殊的依赖性。如果通过体内测量得到验证，作为 SCS 作用机制的一种可能机制，HD SCS 的生物热模型可作为编程优化的工具。
