| Summary: | 碩士 === 國立成功大學 === 物理治療研究所 === 92 === Background and Purpose：Somatosensation allows the nervous system to determine surface orientation as well as the relation between body segments, and thus provides essential sensory input for balance control. Previous studies have shown that experimentally induced changes in the function of the somatosensory system would be accompanied by deterioration in standing balance control. While some of the studies induced unknown degrees of altered sensory condition (i.e. standing on a compliant surface), others induced total sensory loss (i.e. ischemic blockage). However, the relationship between the degree of somatosensory loss and balance deterioration is still not clear. The purpose of this study was to investigate the influence of different degrees of somatosensation loss on standing balance control.
Methods：Twenty-one healthy young subjects were recruited. Three somatosensory statuses, intact, partial loss, and total loss, were manipulated by varying the duration of ischemic blocking of afferent inputs below the ankles. To identify the extent of somatosensory loss induced by ischemic blockage, two sensory tests were performed: 1) touch-pressure threshold (TPT), and 2) current perception threshold (CPT). TPT (reflected the sensitivity to the touch and pressure stimulation) was measured by Semmes-Weinstein Aesthesiometer; CPT (reflected the sensitivity of the large afferent fiber to electrical stimulation), was measured by Neurometer, which emitted a non-aversive transcutaneous electrical stimulus to quantify CPT values. Subjects were asked to perform the following balance tasks：quiet stance with eye open and eye closed；narrow space stance with eye open and eye closed, on a force platform. The following variables of the motion of center of pressure (to reflect the body sway during quiet standing) were calculated for analysis：trajectory, anteroposterior range (AP range), and anteroposterior mean instantaneous velocity (AP velocity).
Results：TPT and CPT were significantly increased according to greater extent of somatosensation loss. In all the balance trials, trajectory and AP velocity were significantly increased in both partial and total loss conditions when comparing to those in intact sensory condition. Between partial and total sensory loss conditions, the trajectory and AP velocity were changed significantly only in the narrow space standing trial, eye closed condition.
Conclusion：Both partial and total loss of somatosensation would deteriorate standing balance control abilities. In addition, deterioration of balance performance was not solely determined by the degree of somatosensory loss, but also by the availability of other sensory sources and the difficulty of the balance task. Thus, when evaluating balance performances of patients with somatosensory dysfunction clinically, attention should be also be given to the availability of other sensory inputs and task difficulty.
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