Validating and testing the versatility of the cumulative head impact index
Hayden, John Parker
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In the study of diseases such as chronic traumatic encephalopathy (CTE), the ability to gather retrospective estimates of an individual’s total repetitive head impacts (RHI) is paramount. Although the exact mechanism responsible for the development of CTE is still unknown, it is well accepted that RHI play a critical role. Until recently, however, the methodology used to collect retrospective estimates of RHI have been very limited. In the beginning of 2016, Montenigro et al. from the Boston University’s Alzheimer’s Disease and CTE Center published a new method of RHI estimation called the Cumulative Head Impact Index (CHII). The CHII was developed by collecting self-reported football histories (years of play, positions of play and levels of play), and using that data to extrapolate the findings of short-term helmet-accelerometer studies into career-long estimates of cumulative head impacts. In addition to publishing this new method, Montenigro et al. (2016) also determined that the CHII was very successful at predicting later-life neurobehavioral and cognitive impairment, an essential ability of any RHI estimate intended to be used in CTE research. Participants in the Montenigro et al. (2016) analysis were part of an ongoing longitudinal study where individuals take yearly surveys of their neurobehavioral and cognitive well-being in addition to answering surveys about sports participation, head injuries and overall wellbeing. Participants had played football at the high school or college level, but had not played any other contact sports. This thesis serves as an initial validation of that publication, and also tests the ability of the CHII to predict later-life impairment in a more diverse population of athletes. Participants in this thesis were selected from the same ongoing longitudinal study according to two distinct sets of inclusion and exclusion criteria. For the purposes of conducting a validation study, the first set of criteria were identical to those used by Montenigro et al. (2016). The second experimental set allowed for participants who had participated in a secondary contact sport if it was at the high school level or below. These two sets of criteria resulted in 70 “validation” participants, and 82 “experimental” participants. Using the same methods as Montenigro et al. 2016, we calculated the CHII for all participants, and examined the ability of the CHII to predict later-life impairment. Our findings validated that the CHII was indeed successful at predicting later-life impairment from cumulative head impacts among the validation group of 70 participants. In particular, the CHII successfully predicted a threshold dose-response relationship between CHI and apathy (p >0.001), depression (p >0.001), executive function dysregulation (p >0.001), and self-reported cognitive impairment (p >0.001). We then found that the CHII was much less successful at predicting impairment in the experimental group of 82, only finding significance in measures of apathy (p=0.0502) and executive function dysregulation (p=0.0277). Overall, our findings indicate that the CHII is an excellent improvement in methods of estimating RHI in people whose only contact sport is football.
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