van Lunteren E, Sankey C B
Departments of Medicine and Neurosciences, Cleveland Veterans Affairs Medical Center and Case Western Reserve University, Cleveland, Ohio 44106, USA.
J Appl Physiol (1985). 2000 Feb;88(2):586-98. doi: 10.1152/jappl.2000.88.2.586.
A high-frequency burst of pulses at the onset of a subtetanic train of stimulation allows skeletal muscle to hold force at a higher level than expected from the extra pulses alone because of the catchlike property of muscle. The present study tested the hypothesis that the presence and degree of force increase induced by a high-frequency burst are strongly modulated by the subsequent train frequency. Rat diaphragm muscle strips (studied in vitro at 37 degrees C) underwent two-, three-, or four-pulse bursts [interpulse interval (IPI) of 5 or 10 ms] at the onset of 10- to 50-Hz subtetanic trains. Force was quantified during the train with respect to its peak value (F(peak)), mean value (F(mean)), and force-time integral (F(area)), and it was compared with that produced during subtetanic trains of an equal number of pulses without preceding pulse bursts (Diff-F(peak), Diff-F(mean), Diff-F(area)). F(peak) and F(mean) increased with two-, three-, and four-pulse bursts, and Diff-F(peak) and Diff-F(mean) increased progressively with decreasing frequency of the subtetanic train. F(area), the best reflection of catchlike force augmentation, was increased mainly by the four-pulse bursts with an IPI of 10 ms, and Diff-F(area) was maximal at subsequent train frequencies of 15-25 Hz. The use of incorrect patterns of burst stimulation could also precipitate F(area) decreases, which were observed with the four-pulse, 5-ms IPI paradigm. The time required to reach 80% of maximal force (T(80%)) became shorter for each of the pulse burst stimulation patterns, with maximal reduction of Diff-T(80%) occurring at a subsequent train frequency of 20 Hz in all cases. These data indicate that extra-pulse burst stimulation paradigms need to incorporate the optimal combinations of extra-pulse number, IPI, and the frequency of the subsequent subtetanic train to take greatest advantage of the catchlike property of muscle.
在不完全强直刺激串开始时的高频脉冲群可使骨骼肌保持比仅额外脉冲预期更高水平的力量，这是由于肌肉的类似强直收缩特性。本研究检验了以下假设：高频脉冲群诱导的力量增加的存在与否及程度受随后刺激串频率的强烈调节。大鼠膈肌肌条（在37℃体外研究）在10至50Hz不完全强直刺激串开始时接受两脉冲、三脉冲或四脉冲群刺激[脉冲间隔（IPI）为5或10毫秒]。在刺激串期间，根据其峰值（F(peak)）、平均值（F(mean)）和力量-时间积分（F(area)）对力量进行量化，并与在无先前脉冲群刺激的相同脉冲数不完全强直刺激串期间产生的力量进行比较（Diff-F(peak)、Diff-F(mean)、Diff-F(area)）。F(peak)和F(mean)随两脉冲、三脉冲和四脉冲群刺激而增加，Diff-F(peak)和Diff-F(mean)随不完全强直刺激串频率降低而逐渐增加。F(area)是类似强直收缩力量增强的最佳反映，主要由IPI为10毫秒的四脉冲群刺激增加，Diff-F(area)在随后15至25Hz的刺激串频率时最大。使用不正确的脉冲群刺激模式也可能导致F(area)降低，在四脉冲、5毫秒IPI模式中观察到这种情况。每种脉冲群刺激模式下达到最大力量（T(80%)）80%所需的时间都变短，在所有情况下，Diff-T(80%)的最大减少发生在随后20Hz的刺激串频率时。这些数据表明，额外脉冲群刺激模式需要纳入额外脉冲数、IPI和随后不完全强直刺激串频率的最佳组合，以最大程度利用肌肉的类似强直收缩特性。
