Postural Control for Standing after Ischemic Nerve Block in One Leg

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  • SAKO Megumi
    Department of Rehabilitation Medicine, Keio University School of Medicine

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  • 阻血による片側下肢の神経遮断が立位姿勢制御に与える影響
  • ソケツ ニ ヨル カタガワ カシ ノ シンケイ シャダン ガ リツイ シセイ セイギョ ニ アタエル エイキョウ

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Abstract

Postural control for standing is carried out by keeping the vertical projection of the center of gravity within the supporting surface confines. Body sway during standing can be estimated from the center of pressure (COP) derived from force plate data, which tracks the center of gravity. In the process of establishing and maintaining a standing posture, somatosensory input from legs plays an important role. In this study, the standing posture organized to compensate for deafferentation induced by ischemic nerve block in one leg was investigated. Nineteen healthy male subjects participated in this experiment with informed consent. Hypoxic ischemia was produced by placing a pneumatic cuff on the right thigh and inflating it up to 300mmHg. The blockade of Ia afferents was determined by the loss of H-reflex on the right gastrocnemius muscle. Postural control during quiet standing was estimated by force platforms, electrogoniometers and surface EMGs. Horizontal displacements of the COP were calculated by using the recorded forces. The COP locations in the anterior-posterior direction were presented as a percentage of longitudinal foot length. Signals during quiet standing were recorded under the following conditions: without any intervention, just after the inflation of the cuff, during the loss of H-reflex but when F-wave was presented (H-, F+), and after the F-wave disappeared (H-, F-). Compared with the standing posture observed after the inflation of the cuff, the right hip and knee were flexed after the ischemic nerve was blocked. The weight over the right leg was reduced by about 15% of the body weight. And the right COP was located about 40mm backward. The ischemic nerve block of the right leg induced deactivation of the right gastrocnemius muscle so the left leg and right proximal muscle activity increased in order to stabilize the standing posture. We did not observe any significant difference between the conditions of (H, F+) and (H-, F-). The instruction to equally bear the weight onto the both legs after the ischemic nerve block induced further activations in the left erector spinae, right vastus medialis, and left tibialis anterior. However there was no significant change in the standing posture including the COP locations. When prescribing rehabilitation therapy, it is very important to understand the process of postural organization after the nerve block in one leg.

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