DiMarco A F, Romaniuk J R, Kowalski K E, Supinski G
Pulmonary Division, Department of Medicine, Case Western Reserve University and MetroHealth Medical Center, Cleveland, Ohio 44109, USA.
J Appl Physiol (1985). 1999 Jun;86(6):1881-9. doi: 10.1152/jappl.1999.86.6.1881.
Large positive airway pressures (Paws) can be generated by lower thoracic spinal cord stimulation (SCS), which may be a useful method of restoring cough in spinal cord-injured patients. Optimal electrode placement, however, requires an assessment of the pattern of current spread during SCS. Studies were performed in anesthetized dogs to assess the pattern of expiratory muscle recruitment during SCS applied at different spinal cord levels. A multicontact stimulating electrode was positioned over the surface of the lower thoracic and upper lumbar spinal cord. Recording electromyographic electrodes were placed at several locations in the abdominal and internal intercostal muscles. SCS was applied at each lead, in separate trials, with single shocks of 0.2-ms duration. The intensity of stimulation was adjusted to determine the threshold for development of the compound action potential at each electrode lead. The values of current threshold for activation of each muscle formed parabolas with minimum values at specific spinal root levels. The slopes of the parabolas were relatively steep, indicating that the threshold for muscle activation increases rapidly at more cephalad and caudal sites. These results were compared with the effectiveness of SCS (50 Hz; train duration, 1-2 s) at different spinal cord levels to produce changes in Paw. Stimulation at the T9 and T10 spinal cord level resulted in the largest positive Paws with a single lead. At these sites, threshold values for activation of the internal intercostal (7-11th interspaces) upper portions of external oblique, rectus abdominis, and transversus abdominis were near their minimum. Threshold values for activation of the caudal portions of the abdominal muscles were high (>50 mA). Our results indicate that 1) activation of the more cephalad portions of the abdominal muscles is more important than activation of caudal regions in the generation of positive Paws and 2) it is not possible to achieve complete activation of the expiratory muscles with a single electrode lead by using modest current levels. In support of this latter conclusion, a two-electrode lead system results in more uniform expiratory muscle activation and significantly greater changes in Paw.
通过下胸段脊髓刺激（SCS）可产生较大的气道正压（Paws），这可能是恢复脊髓损伤患者咳嗽功能的一种有用方法。然而，最佳电极放置需要评估SCS期间电流扩散的模式。在麻醉犬身上进行了研究，以评估在不同脊髓水平施加SCS时呼气肌募集的模式。将一个多触点刺激电极放置在下胸段和上腰段脊髓表面。记录肌电图电极放置在腹部和肋间内肌的几个位置。在单独的试验中，对每个导联施加SCS，单次电击持续时间为0.2毫秒。调整刺激强度以确定每个电极导联产生复合动作电位的阈值。激活每块肌肉的电流阈值值形成抛物线，在特定脊髓神经根水平处具有最小值。抛物线的斜率相对较陡，表明在更高的头侧和尾侧部位，肌肉激活阈值迅速增加。将这些结果与不同脊髓水平的SCS（50Hz；串刺激持续时间，1 - 2秒）产生Paws变化的有效性进行了比较。在T9和T10脊髓水平进行刺激时，单导联产生的正Paws最大。在这些部位，激活肋间内肌（第7 - 11肋间）、腹外斜肌上部、腹直肌和腹横肌的阈值接近其最小值。激活腹部肌肉尾侧部分的阈值较高（>50mA）。我们的结果表明，1）在产生正Paws方面，激活腹部肌肉的头侧部分比激活尾侧区域更重要；2）使用适度电流水平，单电极导联不可能实现呼气肌的完全激活。支持后一结论的是，双电极导联系统可导致呼气肌激活更均匀，且Paws的变化显著更大。
