Abstract
In post-stroke hemiparesis, neural impairment alters muscle control, causing abnormal movement and posture in the affected limbs. A decrease in voluntary use of the paretic arm and flexed posture during rest also induce secondary tissue transformation in the upper limb muscles. To obtain a specific, accurate, and reproducible marker of the current biological status of muscles, we collected visible (VIS) and short-wave Infrared (SWIR) reflectance spectra in vivo using a portable spectroradiometer (350–2500 nm), which provided the spectral fingerprints of the elbow flexors and extensors. We compared the spectra for the affected and unaffected sides in 23 patients with post-stroke hemiparesis (25–87 years, 8 women) and eight healthy controls (33–87 years, 5 women). In eight patients, spectra were collected before and after botulinum toxin injection. Spectra underwent off-line preprocessing, principal component analysis, and partial least-squares discriminant analysis. Spectral fingerprints discriminated the muscle (biceps vs. triceps), neurological condition (normal vs. affected vs. unaffected), and effect of botulinum toxin treatment (before vs. 30 to 40 days vs. 110 to 120 days after injection). VIS-SWIR spectroscopy proved valuable for non-invasive assessment of optical properties in muscles, enabled more comprehensive evaluation of hemiparetic muscles, and provided optimal monitoring of the effectiveness of medication.
Highlights
In post-stroke hemiparesis, neural impairment alters muscle control, causing abnormal movement and posture in the affected limbs
Raw mean spectra for the biceps and triceps were collected for each participant (n = 50/muscle/side/patient, n = 50/muscle/normal subjects, total 5400; raw data in the Supplementary Materials File (SMF), supplementary material 2, Figure S1) and grand averages computed for all classes [affected biceps, unaffected biceps, affected triceps, unaffected triceps, normal biceps, normal triceps (Fig. 1); biceps and triceps (Fig. 2a)], together with standard deviation
The principal component analysis (PCA) score plots showed that the explained variance (EV) for PC1 for biceps vs. triceps was 11.96% (Fig. 2b), affected vs. normal biceps 27.79% (Fig. 3a), affected vs. normal triceps 18.58% (Fig. 3b), affected vs. unaffected biceps 5.99% (Fig. 3c), affected vs. unaffected triceps 4.94% (Fig. 3d), unaffected vs. normal biceps 14.17% (Fig. 3e), and unaffected vs. normal triceps 13.62% (Fig. 3f)
Summary
In post-stroke hemiparesis, neural impairment alters muscle control, causing abnormal movement and posture in the affected limbs. Objective assessment of UMNS signs is a matter of clinical neurophysiology[13] by means of EMG, ENG, and reflex studies, and biomechanics by analysis of kinematics, limb impedance, and torque to mechanical perturbation or voluntary movement[14] Such a comprehensive investigation of muscles is not feasible in clinical practice because it can require specific expertise, devices, and time, as well as cooperation that is hard to elicit in patients, especially children. The collected spectra are surrogates for the complex attributes of the organic structures from which they originate, representing the “fingerprint” of the examined sample This procedure represents an alternative VIS-SWIR spectroscopy application than that aimed to measure real-time non-invasive detection of tissue hemoglobin o xygenation[17], or to detect the hemoglobin and myoglobin content of skeletal m uscle[18]. In our previous study in healthy subjects[15], VIS-SWIR reflectance spectra were able to distinguish the upper limb flexors from extensors and were sensitive to anthropometric variables, such as gender, age, and body mass index
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