|Acute effects of whole-body vibration on spastic hypertonia in patients with chronic stroke
|Pang, Marco (RS)
|FHSS Faculty Distinguished Thesis Award (2018/19)
|Hong Kong Polytechnic University -- Dissertations
Vibration -- Therapeutic use
Brain damage -- Patients -- Rehabilitation
Cerebrovascular disease -- Patients -- Rehabilitation
|Department of Rehabilitation Sciences
|278 pages : color illustrations
|Whole-body vibration (WBV) may be a useful adjunct in the management of spastic hypertonia due to its reported effects on muscles and the nervous system. However, few studies have examined the possible physiological mechanism and therapeutic effects of WBV on spastic hypertonia in people with chronic stroke. Therefore, this thesis aimed to address the knowledge gap which was achieved through a series of five integrated studies. Study 1 (Chapter 2) is a systematic review aimed to examine the effects of WBV on spasticity among people with central nervous system disorders. Based on extensive review of the literature, there was some evidence that WBV may be useful in reducing leg muscle spasticity in cerebral palsy, but the effect was uncertain in multiple sclerosis, stroke and spinocerebellar ataxia. Moreover, the Modified Ashworth Scale was extensively used in the reviewed studies, despite its low reliability, validity, and responsiveness. Studies in high methodological and reporting quality are warranted. As spastic hypertonia has two components in chronic stroke patients, namely, the reflex component (e.g., hyperreflexia) and the non-reflex component (e.g., changes in the mechanical properties of the affected muscles). Study 2 (Chapter 3) aimed to investigate the mechanical properties of the medial gastrocnemius (MG) muscle in chronic stroke survivors using the Supersonic Shear imaging (SSI) technology. The results showed that SSI had good reliability for measuring passive muscle stiffness in people with chronic stroke. Alterations in the architectural properties and poor functional mobility were observed in chronic stroke patients with spastic hypertonia. For WBV applications, both the efficacy and safety of the vibration application should be considered. Thus, Study 3 (Chapter 4) examined the transmission of WBV signals in the human body. The results indicated that vibration transmissibility and signal purity were influenced by the vibration amplitude, frequency, body postures, and their interaction for chronic stroke survivors. With the exception of bilateral ankles, increased vibration frequency, amplitude, or knee flexion angle led to lower the transmissibility. The transmissibility in the paretic side was comparable to the nonparetic sides, excepting that at the ankle during tip-toe standing. In a few conditions at the paretic ankle, knee, knee and hip, more-severe leg motor impairment was correlated with greater transmissibility. No significant association was observed between the leg muscle spasticity and WBV transmissibility. Furthermore, Study 4 (Chapter 5) was conducted to investigate the effect of WBV on neuromuscular activation. The results showed that the addition of WBV to exercise led to a significant increase in muscle activation in the MG and the tibial anterior (TA) and medial hamstrings, but not the vastus medialis, on both paretic and nonparetic sides among individuals with chronic stroke. The effect of WBV was similar on the two sides except TA. Higher muscle activation was associated with larger attenuation of the signals at more proximal anatomical sites, which supports the muscle-tuning mechanism of WBV exercise. In the final study of this thesis (Chapter 6), a randomized cross-over controlled study was conducted. A 5-minutes of WBV intervention was shown to inhibit the soleus H-reflex in the paretic leg by 14% and increase the vascular index of the MG muscle in the same leg by two-fold, and the effect was sustained for 3 or 4 minutes. However, no significant changes were seen in the shear modulus of the MG muscle in the paretic leg after the same WBV intervention. Overall, for clinical application, the thesis indicates that WBV is a safe training modality for people with chronic stroke. WBV frequency, amplitude, body posture can influence the WBV transmissibility, signal purity and WBV-induced muscle activation. Muscle activation could damp the vibration during the WBV. Thus, specific WBV parameters should be carefully set to achieve the intended the therapeutic purpose. WBV may have potential applications in the management of spasticity hypertonia dominated by hyperreflexia and may be a substitute method of exercise to increase peripheral circulation, particularly for frail stroke survivors who cannot participate in other forms of exercise training. However, these postulations will require further research.
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