遺忘性輕度認知功能障礙長者於雙重任務跨越障礙物時下肢動作策略及關節間協調之研究

Abstract

輕度認知障礙是位於正常老化到輕度失智症之間的過渡期，主要以記憶缺損表現的輕度認知障礙，每年約有12%到15%的比例會發展成失智症，此族群除了記憶力缺損，注意力、執行功能等認知功能受到影響之外，動作功能方面發現有平衡控制及步態障礙，為高風險跌倒族群。跨越障礙物是最常見發生跌倒的功能性動作之一，需要精準的身體平衡及端點控制以確保成功且安全跨越障礙物，過去研究探討輕度認知障礙者跨越障礙物的動作分析研究，關注於步態時空參數及其變異性，如跨越速度慢、步長變異大。另一方面，日常生活中我們幾乎很少處於單一任務的情境，過去研究藉由動作-認知雙重任務發現輕度認知障礙相較正常老人需要更多注意力資源以同時進行走路及認知任務。運動-認知雙重任務可評估對認知資源的需求程度，而較差的雙重任務表現與較高的跌倒風險有關。然而，至今研究於輕度認知障礙進行跨越障礙物時之下肢動作策略及關節間協調性，以及動作-認知雙重任務對其之影響皆尚未釐清。 因此，本研究探討輕度認知障礙者跨越障礙物時之下肢動作策略及關節間協調之模式及變異性，以及分散注意力對於輕度認知障礙者於雙重任務跨越障礙時採用之下肢動作策略及關節間協調性的影響。

本研究收取12位輕度認知障礙組及12位年齡相符之健康老人組。身上各黏貼41顆紅外線反光球，赤足以自選速度於測力板步道行走及跨越3種不同高度（10%, 20% 及 30% 腳長）之障礙物，以及跨越障礙物同時進行認知任務（雙重任務）。反光球軌跡藉由8台立體紅外線攝影機捕捉，步態事件，如腳跟落地及離地以3塊測力板及立體紅外線攝影機資訊獲得。 研究結果顯示輕度認知障礙者採用特定動作策略，在前腳跨越時，骨盆前傾角、擺盪腳之髖外展及膝內收角度皆增加；在後腳跨越時，骨盆後傾角、擺盪腳之踝背屈角度皆減少，以成功地保持前腳跨越及後腳跨越之大拇指與障礙物間隙。透過謹慎、保守的策略，輕度認知障礙者在身體重心轉移時，後腳膝踝關節間的協調變異減低。雙重任務引發輕度認知障礙及健康老年者採用特定的下肢動作策略以增加執行雙重任務跨越障礙物時的大拇指與障礙物間隙距離，在前腳跨越時，骨盆前傾角及擺盪腳之髖外展角度皆增加，然站立腳之髖內收角度減少；在後腳跨越時，骨盆後傾角增加，然骨盆上傾角、擺盪腳之膝外展和踝背屈角皆減少。雙重任務跨越障礙物時，輕度認知障礙長者在雙腳支撐期於前腳跨越時髖膝關節之協調及後腳跨越時膝踝關節之協調變異性皆增加，藉由超過輕度認知障礙長者的認知資源之雙重任務，以凸顯其動作協調障礙，顯示於關節間協調的變異性增加。定期監測跨越障礙物的動作控制和關節間協調之模式及變異性，可了解跨越障礙物下肢動作策略中腳趾與障礙物間隙及任何跨越障礙物策略之變化跡象，助於早期發現單一領域遺忘性輕度認知障礙長者於跨越障礙物時的折衷現象。本研究提供臨床人員制定更好的防止跌倒策略，並更好地利用跨越障礙物及雙重任務於復健治療計劃中，提供臨床評估、預防跌倒及復健治療之重要方針。

Mild cognitive impairment (MCI) is considered as a stage of transition, commonly used to describe cognitive impairment, between healthy older people and mild dementia. The annual incidence of dementia in MCI is about 12-15% in developing dementia. Memory, executive function and attention, aberrant postural control and balance disorders during gait are deficit in MCI. Older adults with MCI have a higher risk of falls than cognitively normal adults. One of the most prevalent reasons for falls among older individuals is obstacle-crossing. A safe and successful obstacle-crossing requires precision balance and endpoint control. Higher-order cognitive functions have been shown to restrict obstacle negotiation abilities in MCI, with reduced crossing speeds and greater step lengths variabilities when crossing a fixed-height obstacle. On the other hand, we rarely only perform only one task at a time in the activities of daily living. Studies on cognitive-motor interference using dual-task (DT) conditions also found that patients with MCI required more attentional resources during gait than normal controls. The motor-cognitive dual tasks could evaluate the demands on cognitive resources and the poor dual-task performance is associated with an increased falls risk. However, studies on MCI during more challenging obstacle-crossing and cognitive-motor DT by three dimensional motion analysis system, have been limited. Therefore, the purposes of the current dissertation were to investigate the kinematic strategies and patterns and variability of inter-joint coordination during obstacle-crossing between MCI and healthy control groups; to quantify the effect of divided attention on kinematic strategies and patterns and variability of inter-joint coordination during dual task obstacle-crossing (DT-OBS) between MCI and healthy control groups.

Kinematic strategies and inter-joint coordination in twelve patients with MCI and twelve aged-matched healthy older adults were determined using a motion capture system and forceplates. The current results suggest that patients with MCI were able to maintain normal leading and trailing toe-obstacle clearances for all tested obstacle heights by employing a specific kinematic strategy, namely increased pelvic anterior tilt, swing hip abduction and knee adduction during leading-limb crossing, and decreased pelvic posterior tilt and swing ankle dorsiflexion during trailing-limb crossing. By adopting a cautious strategy, MCI crossed obstacle successfully with decreased variability of trailing knee-ankle coordination over body-weight transfer. Dual task provoked the MCI and healthy older groups to cross obstacle with increased toe-obstacle clearance using a specific kinematic strategy, namely increased pelvic anterior tilt, swing hip abduction but decreased stance hip adduction during leading-limb crossing, and increased pelvic posterior tilt but decreased pelvic upward list, swing knee abduction and ankle plantarflexion during trailing-limb crossing. As a result of such compromise strategy, the increased variabilities in coordination of leading hip-knee and trailing knee-ankle over DLS were revealed through the exceed cognitive resources for MCI to showed their subtle motor dysfunction. Regular monitoring of obstacle-crossing kinematics and inter-joint coordination for reduced toe-obstacle clearance or any signs of changes in crossing strategy may be helpful for early detection of compromised ability to cross obstacles in patients with single-domain aMCI. The findings could be useful in establishing better fall-prevention strategies and making better use of the obstacle-crossing task in rehabilitation programs.