Patel Prakruti J, Bhatt Tanvi
Department of Physical Therapy, University of Illinois at Chicago, United States.
Department of Physical Therapy, University of Illinois at Chicago, United States.
Neuroscience. 2016 Oct 1;333:252-63. doi: 10.1016/j.neuroscience.2016.06.044. Epub 2016 Jul 11.
We examined whether aging with and without a cerebral lesion such as stroke affects modulation of reactive balance response for recovery from increasing intensity of sudden slip-like stance perturbations. Ten young adults, older age-match adults and older chronic stroke survivors were exposed to three different levels of slip-like perturbations, level 1 (7.75m/s(2)), Level II (12.00m/s(2)) and level III (16.75m/s(2)) in stance. The center of mass (COM) state stability was computed as the shortest distance of the instantaneous COM position and velocity relative to base of support (BOS) from a theoretical threshold for backward loss of balance (BLOB). The COM position (XCOM/BOS) and velocity (ẊCOM/BOS) relative to BOS at compensatory step touchdown, compensatory step length and trunk angle at touchdown were also recorded. At liftoff, stability reduced with increasing perturbation intensity across all groups (main effect of intensity p<0.05). At touchdown, while the young group showed a linear improvement in stability with increasing perturbation intensity, such a trend was absent in other groups (intensity×group interaction, p<0.05). Between-group differences in stability at touchdown were thus observed at levels II and III. Further, greater stability at touchdown positively correlated with anterior XCOM/BOS however not with ẊCOM/BOS. Young adults maintained anterior XCOM/BOS by increasing compensatory step length and preventing greater trunk extension at higher perturbation intensities. The age-match group attempted to increase step length from intensity I to II to maintain stability however could not further increase step length at intensity III, resulting in lower stability on this level compared with the young group. Stroke group on the other hand was unable to modulate compensatory step length or control trunk extension at higher perturbation intensities resulting in reduced stability on levels II and III compared with the other groups. The findings reflect impaired modulation of recovery response with increasing intensity of sudden perturbations among stroke survivors compared with their healthy counter parts. Thus, aging superimposed with a cortical lesion could further impair reactive balance control, potentially contributing toward a higher fall risk in older stroke survivors.
我们研究了伴有或不伴有诸如中风等脑部病变的衰老是否会影响对突然滑倒样姿势扰动强度增加时恢复的反应性平衡反应的调节。10名年轻成年人、年龄匹配的老年人和老年慢性中风幸存者在站立时暴露于三种不同水平的滑倒样扰动，即水平1（7.75m/s(2)）、水平II（12.00m/s(2)）和水平III（16.75m/s(2)）。质心（COM）状态稳定性通过相对于支撑基底（BOS）的瞬时COM位置和速度到向后失去平衡（BLOB）理论阈值的最短距离来计算。还记录了补偿性步触地时相对于BOS的COM位置（XCOM/BOS）和速度（ẊCOM/BOS）、补偿性步长以及触地时的躯干角度。在离地时，所有组的稳定性都随着扰动强度的增加而降低（强度主效应p<0.05）。在触地时，虽然年轻组的稳定性随着扰动强度的增加呈线性改善，但其他组没有这种趋势（强度×组交互作用，p<0.05）。因此，在水平II和III观察到触地时组间稳定性差异。此外，触地时更高的稳定性与前向XCOM/BOS呈正相关，但与ẊCOM/BOS无关。年轻成年人通过增加补偿性步长并在更高扰动强度下防止更大的躯干伸展来维持前向XCOM/BOS。年龄匹配组试图从强度I到II增加步长以维持稳定性，但在强度III时无法进一步增加步长，导致该水平的稳定性低于年轻组。另一方面，中风组在更高扰动强度下无法调节补偿性步长或控制躯干伸展，导致与其他组相比在水平II和III的稳定性降低。研究结果反映出与健康对照组相比，中风幸存者中随着突然扰动强度增加，恢复反应的调节受损。因此，叠加皮质病变的衰老可能会进一步损害反应性平衡控制，可能导致老年中风幸存者更高的跌倒风险。
