Department of Biomedical Engineering, Virginia Commonwealth University, Richmond, Virginia, USA.
Restor Neurol Neurosci. 2022;40(3):169-184. doi: 10.3233/RNN-221254.
Assessment of voluntary activation is useful in the study of neuromuscular impairments, particularly after spinal cord injury (SCI). Measurement of voluntary activation with transcranial magnetic stimulation (VATMS) is limited by technical challenges, including the difficulty in preferential stimulation of cortical neurons projecting to the target muscle and minimal stimulation of antagonists. Thus, the motor evoked potential (MEP) response to TMS in the target muscle compared to its antagonist may be an important parameter in the assessment of VATMS.
The purpose of this study was to evaluate the effect of isometric elbow flexion angle on two metrics in individuals with tetraplegia following SCI: 1) the ratio of biceps/triceps MEP amplitude across a range of voluntary efforts, and 2) VATMS.
Ten individuals with tetraplegia and ten nonimpaired individuals were recruited to participate in three sessions wherein VATMS was assessed at 45°, 90°, and 120° of isometric elbow flexion.
In SCI participants, the biceps/triceps MEP ratio was not modulated by elbow angle. In nonimpaired participants, the biceps/triceps MEP ratio was greater in the more flexed elbow angle (120° flexion) compared to 90° during contractions of 50% and 75% MVC, but VATMS was not different. VATMS assessed in the more extended elbow angle (45° flexion) was lower relative to 90° elbow flexion; this effect was dependent on the biceps/triceps MEP ratio. In both groups, VATMS was sensitive to the linearity of the voluntary moment and superimposed twitch relationship, regardless of elbow angle. Linearity was lower in SCI relative to nonimpaired participants.
Increasing the MEP ratio via elbow angle did not enable estimation of VATMS in SCI participants. VATMS may not be a viable approach to assess neuromuscular function in individuals with tetraplegia.
在研究神经肌肉损伤，特别是脊髓损伤（SCI）后，对自愿激活的评估是有用的。经颅磁刺激（TMS）的自愿激活测量受到技术挑战的限制，包括优先刺激投射到目标肌肉的皮质神经元的困难和对拮抗剂的最小刺激。因此，与目标肌肉相比，TMS 对目标肌肉的运动诱发电位（MEP）反应及其拮抗剂可能是评估 VATMS 的一个重要参数。
本研究旨在评估等长肘部弯曲角度对 SCI 后四肢瘫痪个体的两个指标的影响：1）在一系列自愿努力中，二头肌/三头肌 MEP 幅度的比值，以及 2）VATMS。
招募了 10 名四肢瘫痪患者和 10 名非残疾个体参加了三个会话，其中在 45°、90°和 120°的等长肘部弯曲时评估了 VATMS。
在 SCI 参与者中，二头肌/三头肌 MEP 比值不受肘部角度的调制。在非残疾参与者中，与 90°肘部弯曲相比，在 50%和 75%MVC 的更弯曲肘部角度（120°弯曲）下，二头肌/三头肌 MEP 比值更大，但 VATMS 没有差异。在更伸展的肘部角度（45°弯曲）下评估的 VATMS 相对于 90°肘部弯曲较低；这种效果取决于二头肌/三头肌 MEP 比值。在两组中，VATMS 对自愿力矩和叠加抽搐关系的线性敏感，无论肘部角度如何。与非残疾参与者相比，SCI 中的线性度较低。
通过肘部角度增加 MEP 比值并不能使 SCI 参与者估计 VATMS。VATMS 可能不是评估四肢瘫痪个体神经肌肉功能的可行方法。
