Abstract
Automated wireless sensing of force dynamics during a visuomotor control task was used to rapidly assess residual motor function during finger pinch (right and left hand) and lower lip compression in a cohort of seven adult males with chronic, unilateral middle cerebral artery (MCA) stroke with infarct confirmed by anatomic magnetic resonance imaging (MRI). A matched cohort of 25 neurotypical adult males served as controls. Dependent variables were extracted from digitized records of ‘ramp-and-hold’ isometric contractions to target levels (0.25, 0.5, 1, and 2 Newtons) presented in a randomized block design; and included force reaction time, peak force, and dF/dtmax associated with force recruitment, and end-point accuracy and variability metrics during the contraction hold-phase (mean, SD, criterion percentage ‘on-target’). Maximum voluntary contraction force (MVCF) was also assessed to establish the force operating range. Results based on linear mixed modeling (LMM, adjusted for age and handedness) revealed significant patterns of dissolution in fine force regulation among MCA stroke participants, especially for the contralesional thumb-index finger followed by the ipsilesional digits, and the lower lip. For example, the contralesional thumb-index finger manifest increased reaction time, and greater overshoot in peak force during recruitment compared to controls. Impaired force regulation among MCA stroke participants during the contraction hold-phase was associated with significant increases in force SD, and dramatic reduction in the ability to regulate force output within prescribed target force window (±5% of target). Impaired force regulation during contraction hold-phase was greatest in the contralesional hand muscle group, followed by significant dissolution in ipsilateral digits, with smaller effects found for lower lip. These changes in fine force dynamics were accompanied by large reductions in the MVCF with the LMM marginal means for contralesional and ipsilesional pinch forces at just 34.77% (15.93 N vs. 45.82 N) and 66.45% (27.23 N vs. 40.98 N) of control performance, respectively. Biomechanical measures of fine force and MVCF performance in adult stroke survivors provide valuable information on the profile of residual motor function which can help inform clinical treatment strategies and quantitatively monitor the efficacy of rehabilitation or neuroprotection strategies.
Highlights
Ischemic brain damage associated with cerebrovascular stroke is the second leading cause of disability and death worldwide [1]
A full series of ramp-and-hold force trials during thumb-index finger pinch, and lower lip compression are shown in Figure 1 for a 63 year-old neurotypical male and a 66 year-old male who survived a right middle cerebral arteries (MCA) ischemic stroke
Linear mixed modeling (LMM) for reaction time revealed a significant interaction between stroke and muscle group after controlling for participant’s age and handedness (F(2,3760) = 27.25, p < 0.0001)
Summary
Ischemic brain damage associated with cerebrovascular stroke is the second leading cause of disability and death worldwide [1]. Dysfunction during intricate movements of the fingers or orofacial muscle groups is often prominent in post-stroke survivors, as brain lesions that damage cortical upper motor neurons degrade motor units through trans-synaptic mechanisms, in high density, monosynaptic motoneuron pools which control the fingers of the hand and perioral structures [6,7,8,9,10]. Ischemic brain lesions can adversely affect hand and digits during precision grip or pinch force stability, and movement accuracy during object manipulation and reach [11,12,13]. Following an infarct in the territory of the middle cerebral arteries (MCA) which feed the elaborated sensorimotor cortical representations of the hand and fingers, a loss of higher-order motor planning and sensorimotor integration greatly disrupts fine force production, during individuation of the digits and strength. This, combined with the loss of descending modulatory control, often results in spasticity and contraction instability during attempts at highly controlled fine force production [18,19,20,21]
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