Date of Award
Doctor of Philosophy in Biomedical Engineering - (Ph.D.)
Karen J. Nolan
Xianlian Alex Zhou
Falls are a major burden on healthcare infrastructure, especially in older adults and even more so in older individuals that are living in institutions. According to data from the Centers for Disease Control and Prevention (CDC), from 2010 to 2020, unintentional falls were the leading cause of nonfatal emergency department visits for all age groups except among individuals from 15-24 years of age, where unintentional falls ranked a very close second to being unintentionally struck by or against. Among older individuals living in the community, approximately 30-35% fall at least once in a given year, and around three times as many falls over the same time period among adults living in institutions. Sustaining a fall can double an older individual's chances of sustaining a subsequent fall, and about one in five falls results in some kind of serious injury, such as a broken bone or head injury, with falls being the leading cause of traumatic brain injury (TBI).
Based on the CDC's 2014 data set, about 2 8 million people sustain a TBI in the United States every year, including over 837,000 children, contributing to over 56,000 deaths with over 2,500 of them being children. During this period, falls were the leading cause of TBI, accounting for approximately 48% of all TBI related emergency room (ER) visits, with older adults 65 and older and children ages 17 and below being most likely to suffer a TBI as a result of a fall, with falls being the cause in 49% and 81% of cases, respectively. Depending on the exact nature and severity of a particular TBI, the resulting impairments can be both acute and long lasting, range from mild to debilitating, and can include sensory and perceptual deficiencies, reduced or altered cognitive function, and various types of motor deficits including paralysis, spasticity, and weakness. Balance dysfunction is a significant disabling factor post TBI, as it can increase the risk of falls which can in turn lead to subsequent brain injuries.
Postural control, the process of maintaining one's balance, is an essential ability that plays a crucial role in many everyday activities and is accomplished through the integration and coordination of visual, vestibular, proprioceptive inputs, and motor control to create a feedback system that maintains the body's center of mass (COM) above its' base of support. A TBI can affect postural control in multiple different ways, including direct damage to sensory processing regions responsible for handling essential balance related internal and external stimuli, or damaging motor control and planning areas that are responsible for generating appropriate muscular response to the above-mentioned stimuli. While damage to either of these cortical regions can lead to balance dysfunction, the specific regions effected, and the extent of the damage can necessitate different rehabilitation approaches when attempting to restore lost functionality. A loss or reduction of a particular sensory input or the ability to process that sensory input may require training an individual to shift their focus to the remaining sensory inputs, while the loss or reduction of motor control to a limb or joint would require the training of an individual to develop and utilize compensatory motor strategies for other limbs and joints to safely maintain their balance.
When standing quietly (or moving in an unperturbed fashion), an individual's postural control system only needs to account for internal changes resulting from the body's own movements, and the individual is more easily able to control the timing and intensity of required postural adjustments by limiting their movements to within the range of what their sensory and motor control systems can handle, i.e., if they have reduced muscle strength, perception, or reaction time, they can limit the speed or extent of their movements to make it easier for them to maintain their balance, rather than moving rapidly. However, when an individual's base of support is perturbed unexpectedly, their body needs to be able to determine and perform the necessary postural adjustments based on the perturbation that occurred, which can pose an increasing challenge depending upon the extent of injuries. Since they are less in control of the dynamics of the situation, their ability to perceive the perturbation is critical to their ability to adapt to it properly. The slower or less accurately they perceive the disturbance the less likely they are to be able to make the minimum postural adjustments needed to maintain stability, and the more likely they become to require exaggerated or significant postural adjustments that may be beyond their ability to safely perform. Since falls are a major concerned, as mentioned above, and falls occur when the central nervous system fails to identify an impending loss of balance and or make the necessary adjustments to an individual's COM or base of support in time, an individual's ability to accurately perceive their environment during dynamic situations is critical to avoiding falls. Existing research that specifically quantifies impaired sensory integration in an objective manner post TBI is limited, and no prior work has investigated sensory acuity in individuals post TBI. While there are many well establish methods for testing postural function that have been validated in both healthy individuals and individuals with a variety of diagnoses, the evidence of these measures in association with balance interventions in individuals post TBI is sparse. To address this deficiency, this preliminary study employed a novel psychophysical approach to assess the perception of perturbation threshold of individuals post TBI and evaluate their kinematic and center of pressure (COP) behaviors during perturbed standing to attempt to detect differences in how individuals post TBI employ known balance control strategies.
Ehrenberg, Naphtaly, "Biomechanical and psychophysical underpinnings of balance dysfunction in individuals with traumatic brain injury" (2023). Dissertations. 1661.