Allostatic load and heterogeneity of outcome after head injury

Wainman-Lefley, Jessica (2017) Allostatic load and heterogeneity of outcome after head injury. PhD thesis, University of Glasgow.

Abstract

Background:
Outcome after head injury is heterogeneous; in particular, late outcome including disability and increased risk of mortality are only partly explained by the severity of the injury and demographic factors (McMillan et al., 2014; McMillan et al., 2012; Whitnall et al., 2006). The allostatic load model conceptualises how stressors can chronically elevate physiological activity and impact on health (McEwen, 1998b). Allostatic load has been shown to be associated with psychosocial functioning, morbidity, and mortality and can predict these outcomes at follow-up; however, it has never been investigated with outcome in the head injury population. The studies in this thesis explore the extent to which allostatic load is associated with cognitive and disability outcome, and change in disability over time after head injury.

Methods:
A systematic search was conducted to inform how to measure allostatic load; 15 indicators of health were assessed representing immune, cardiovascular, anthropometric, metabolic, and neuroendocrine system functioning, and were combined using a summation z-score method to create allostatic load scores. Four empirical studies were conducted to investigate the relationship between allostatic load and outcome after head injury; at discharge from hospital in severe head injury participants (n = 35), at 6 month follow-up (n = 28), late (median 27 years) after head injury (n = 41), and late after repeat concussion in retired international rugby players (n = 48). Allostatic load was also compared with cognitive function late after head injury and repeat concussion and with change in disability between hospital discharge and 6 month follow-up, and from 6 months post-discharge to late after injury. In all the studies, the allostatic load scores of head injury participants were compared to that of non-head injured comparison participants.

Results:
The studies within this thesis found limited evidence to suggest that allostatic load was associated with outcome after head injury. There was no association between allostatic load and disability outcome, change in disability over time, or cognitive function in the severe head injury studies. There was a significant relationship between higher neuroendocrine component scores at hospital discharge and worse disability outcome at 6 month follow-up, indicating possible pathophysiological consequences of neuroendocrine indicators early after injury. Also, the finding that head injury participants had higher anthropometric and metabolic component scores than comparison participants late after injury, and that greater disability over a median of 27 years was associated with higher metabolic component scores, indicates that brain damage causes an increase in secondary outcomes of allostatic load, which potentially has implications of an increased risk of morbidities over time. There was no association between allostatic load and frequency of concussions and therefore a number of outcomes in the retired international rugby player group; with the exception of an unexpected inverse relationship between allostatic load and time to complete a fine motor co-ordination task.

Conclusion:
Findings from this thesis do not support the hypothesis that accumulated physiological dysregulation explain the heterogeneity after head injury. Some of the findings in this thesis require further study to investigate the pathophysiological consequences of higher neuroendocrine indicators at hospital discharge and metabolic indicators late after injury. Also it is important to understand the causes of increased metabolic and anthropometric component scores late after head injury to explore potential interventions to reduce possible increased risk of morbidities and mortality. The atypical findings in the investigation of allostatic load and repeat concussion indicate the accumulation of allostatic load in elite athletes is different to the general population. As none of the studies presented in this thesis found evidence for an association between allostatic load and disability outcome, there is a clear need for more research into factors that predict the heterogeneity of outcome after head injury.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: Head injury, brain injury, allostatic load.
• Subjects: B Philosophy. Psychology. Religion > BF Psychology
• Colleges/Schools: College of Medical Veterinary and Life Sciences > School of Health & Wellbeing > Mental Health and Wellbeing
• Supervisor's Name: McMillan, Professor Tom, Cavanagh, Professor Jonathan and Pell, Professor Jill
• Date of Award: 2017
• Depositing User: Ms Jessica Wainman-Lefley
• Unique ID: glathesis:2017-7931
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 15 Feb 2017 08:56
• Last Modified: 15 Mar 2017 15:11
• URI: https://theses.gla.ac.uk/id/eprint/7931