BackgroundElectrical stimulation is widely used in experimental pain research but it lacks selectivity towards small nociceptive fibers. When using standard surface patch electrodes and rectangular pulses, large fibers are activated at a lower threshold than small fibers. Pin electrodes have been designed for overcoming this problem by providing a higher current density in the upper epidermis where the small nociceptive fibers mainly terminate. At perception threshold level, pin electrode stimuli are rather selectively activating small nerve fibers and are perceived as painful, but for high current intensity, which is usually needed to evoke sufficient pain levels, large fibers are likely co-activated. Long duration current has been shown to elevate the threshold of large fibers by the mechanism of accommodation. However, it remains unclear whether the mechanism of accommodation in large fibers can be utilized to activate small fibers even more selectively by combining pin electrode stimulation with a long duration pulse.ResultsIn this study, perception thresholds were determined for a patch- and a pin electrode for different pulse shapes of long duration. The perception threshold ratio between the two different electrodes was calculated to estimate the ability of the pulse shapes to preferentially activate small fibers. The perception threshold ratios were compared between stimulation pulses of 5- and 50 ms durations and shapes of: exponential increase, linear increase, bounded exponential, and rectangular. Qualitative pain perception was evaluated for all pulse shapes delivered at 10 times perception threshold. The results showed a higher perception threshold ratio for long duration 50 ms pulses than for 5 ms pulses. The highest perception threshold ratio was found for the 50 ms, bounded exponential pulse shape. Results furthermore revealed different strength-duration relation between the bounded exponential- and rectangular pulse shapes. Pin electrode stimulation at high intensity was mainly described as “stabbing”, “shooting”, and “sharp”.ConclusionThese results indicate that long duration pulses with a bounded exponential increase preferentially activate the small nociceptive fibers with a pin electrode and concurrently cause elevated threshold of large non-nociceptive fibers with patch electrodes.

中文翻译：

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通过小针电极优先激活小皮肤纤维也取决于长时间电流的形状

背景电刺激广泛用于实验性疼痛研究，但它对小的伤害感受纤维缺乏选择性。当使用标准表面贴片电极和矩形脉冲时，大纤维的激活阈值低于小纤维。针电极被设计用于通过在上表皮中提供更高的电流密度来克服这个问题，在那里小的伤害性纤维主要终止。At perception threshold level, pin electrode stimuli are rather selectively activating small nerve fibers and are perceived as painful, but for high current intensity, which is usually needed to evoke sufficient pain levels, large fibers are likely co-activated. 已显示长持续时间电流可通过调节机制提高大纤维的阈值。然而，尚不清楚通过将针电极刺激与长持续时间脉冲相结合，是否可以利用大纤维中的调节机制更有选择性地激活小纤维。 结果在这项研究中，针对不同的贴片和针电极确定了感知阈值。持续时间长的脉冲形状。计算两个不同电极之间的感知阈值比以估计脉冲形状优先激活小纤维的能力。对 5 和 50 ms 持续时间的刺激脉冲和以下形状的感知阈值比率进行比较：指数增加、线性增加、有界指数和矩形。对以 10 倍感知阈值传递的所有脉冲形状进行定性疼痛感知评估。结果表明，与 5 ms 脉冲相比，长持续时间 50 ms 脉冲的感知阈值比率更高。对于 50 ms、有界指数脉冲形状，发现了最高的感知阈值比率。结果进一步揭示了有界指数和矩形脉冲形状之间不同的强度-持续时间关系。高强度的针电极刺激主要被描述为“刺”、“射”和“尖锐”。结论这些结果表明，具有有限指数增加的长持续时间脉冲优先激活针电极的小伤害感受纤维，同时导致阈值升高带有贴片电极的大型非伤害性纤维。结果进一步揭示了有界指数和矩形脉冲形状之间不同的强度-持续时间关系。高强度的针电极刺激主要被描述为“刺”、“射”和“尖锐”。结论这些结果表明，具有有限指数增加的长持续时间脉冲优先激活针电极的小伤害感受纤维，同时导致阈值升高带有贴片电极的大型非伤害性纤维。结果进一步揭示了有界指数和矩形脉冲形状之间不同的强度-持续时间关系。高强度的针电极刺激主要被描述为“刺”、“射”和“尖锐”。结论这些结果表明，具有有限指数增加的长持续时间脉冲优先激活针电极的小伤害感受纤维，同时导致阈值升高带有贴片电极的大型非伤害性纤维。