Department of Mechanical Engineering, The University of Auckland, Auckland, New Zealand. Dodd Walls Centre for photonic and Quantum Technologies, Dunedin, New Zealand.
Physiol Meas. 2019 Apr 3;40(3):034006. doi: 10.1088/1361-6579/ab0c24.
To establish suitable frequency spacing and demodulation steps to use when extracting impedance changes from frequency division multiplexed (FDM) carrier signals in peripheral nerve.
Experiments were performed in vitro on cadavers immediately following euthanasia. Neural activity was evoked via stimulation of nerves in the hind paw, while carrier signals were injected, and recordings obtained, with a dual ring nerve cuff implanted on the sciatic nerve. Frequency analysis of recorded compound action potentials (CAPs) and extracted impedance changes, with the latter obtained using established demodulation methods, were used to determine suitable frequency spacing of carrier signals, and bandpass filter (BPF) bandwidth and order, for a frequency multiplexed signal.
CAPs and impedance changes were dominant in the frequency band 200 to 500 Hz and 100 to 200 Hz, respectively. A Tukey window was introduced to remove ringing from Gibbs phenomena. A ±750 Hz BPF bandwidth was selected to encompass 99.99% of the frequency power of the impedance change. Modelling predicted a minimum BPF order of 16 for 2 kHz spacing, and 10 for 4 kHz spacing, were required to avoid ringing from the neighbouring carrier signal, while FDM experiments verified BPF orders of 12 and 8, respectively, were required. With a notch filter centred on the neighbouring signal, a BPF order of at least 6 or 4 was required for 2 and 4 kHz, respectively.
The results establish drive frequency spacing and demodulation settings for use in FDM electrical impedance tomography (EIT) experiments, as well as a method for their selection, and, for the first time, demonstrates the viability of FDM-EIT of neural activity on peripheral nerve, which will be a central aspect of future real-time neural-EIT systems and EIT-based neural prosthetics interfaces.
确定在提取周围神经中频分复用（FDM）载波信号中的阻抗变化时，应使用的合适频率间隔和解调步骤。
在安乐死后立即对尸体进行了体外实验。通过刺激后爪的神经来诱发神经活动，同时将双环神经袖套植入坐骨神经上以注入载波信号并进行记录。通过记录的复合动作电位（CAP）的频率分析和提取的阻抗变化（使用已建立的解调方法获得），确定载波信号的合适频率间隔以及带通滤波器（BPF）带宽和阶数，以实现频率复用信号。
CAP 和阻抗变化分别在 200 至 500 Hz 和 100 至 200 Hz 的频段中占主导地位。引入了 Tukey 窗口以消除 Gibbs 现象的振铃。选择了 ±750 Hz 的 BPF 带宽来包含阻抗变化频率功率的 99.99％。建模预测，为避免来自相邻载波信号的振铃，2 kHz 间隔需要最小 BPF 阶数为 16，4 kHz 间隔需要 10，而 FDM 实验分别验证需要 BPF 阶数为 12 和 8。使用中心位于相邻信号的陷波滤波器，2 和 4 kHz 分别需要至少 6 或 4 的 BPF 阶数。
该结果确定了 FDM 电导率断层成像（EIT）实验中使用的驱动频率间隔和解调设置，以及选择它们的方法，并且首次证明了 FDM 对周围神经神经活动的可行性，这将是未来实时神经-EIT 系统和基于 EIT 的神经假体接口的核心方面。
