Effect of Chronic Hyperthermia in Firefighters on Cognitive Function and Postural Stability A thesis submitted to the Graduate School of the University of Cincinnati in partial fulfilment of the requirements for the degree of Master of Science in the Department of Environmental Health of the College of Medicine 2019 by Nell Wickstrom B.S. Miami University, 2015 Committee Chair: Amit Bhattacharya, Ph.D Page 1 of 144 ABSTRACT Purpose: The purpose of this pilot study is to measure the effect of chronic heat on postural balance characteristics and decision making by comparing firefighters with a long work experience to firefighters who have a much shorter work experience, in terms of years. Methods: Eight fulltime, male firefighters (33.92 years old ± 1.51) participated in this study. Firefighters perceived judgement of others’ fall risk was assessed while undergoing a functional magnetic resonance imaging (fMRI) as they viewed actors in various states of imbalance while walking or standing still. Firefighter’s postural balance was assessed with a wearable, inertial sensor system quantifying spatiotemporal parameters of gait as well as angular velocity, angular displacement, and angular acceleration for phase plane analysis along the medial-lateral (ML) and anterior-posterior (AP) planes. Participants performed static tests while on a force platform to assess these parameters during one-and two-feet balance tests with eyes open and closed. An instrumented timed up and go test (iTUG) was performed to assess dynamic parameters of gait and phase plane analysis. Firefighters perceived judgement of their own fall risk was determined during static and dynamic testing. Results: Firefighters were divided into two groups to compare firefighters with less than 8 years of work experience [Group 1: (3.00 years ± 2.83)] to firefighters with greater than 8 years [Group 2: (13.92 years ± 2.62)]. Between variance of double stance times during dual task was statistically significant (p = 0.013) between Group 1 (5.19e-04 ± (3.36e-04) and Group 2 (4.36e- 3 ± (2.50e-03)). Firefighters who have worked more years (Group 2) have a larger variability between trials for the amount of time they have both feet on the ground during the double stance gait cycle. Significant associations (p-values ranging between 0.018 and 0.061) were found between gait dual task objective variables and gait PSPSI analysis, but not with respect to group. Page 2 of 144 No significant correlations (p-values ranging between 0.165 and 0.980) were found between perceived judgement (as measured by PSPSI metric) of fall risk and history of firefighting. Significant associations (p-values ranging between 0.000173 and 0.100) were found between the two groups for static and dynamic postural balance. Postural sway analysis determined a significant increase in variance (p = 0.000173) along the AP plane for Group 1 firefighters (40.29 ± (1.32)) with less years of work experience in comparison with Group 2 (11.36 ± (7.83)). Variability may indicate central nervous system (CNS) impairments; however, a small sample size may be a contributing factor. Conclusions: Greater double stance variability during dynamic task for firefighters with more years worked may be due to underlying CNS impairments affecting postural stability. Nearly all firefighters portrayed similar concordance when comparing how they perceived fall risk of others revealing the number of years worked as a firefighter had no effect on their perception of fall risk. A consensus model was created from these curves to express a gold standard of perception to be used for future studies. Gait and postural sway results were inconclusive due to small sample size. Future studies are recommended. Page 3 of 144 Page 4 of 144 ACKNOWLEDGMENT There are many individuals that have supported me as I have pursued my degree. I’d first like to thank my academic advisor, Dr. Amit Bhattacharya, for his continual support and guidance. Dr. Bhattacharya has continually aided me throughout the degree process to which I am endlessly grateful. I would also like to thank Dr. Marepalli Rao for his assistance with statistical analysis. Dr. Rao has donated so much of his time to teach and guide me, and I am extremely grateful for his patience throughout this process. I would also like to thank all of the colleagues at the Ergonomics-Biomechanics Laboratory, particularly Cyndy Cox, Lorenna Altman, Rachel Zeiler, Ashley Turner, Nick Ferrara, and Kerrie Dailey. This study was truly a team effort, and no single individual could have performed the extensive methods and collected all of the data alone. Thank you all so much for your persistence, time, and effort. Thank you also to Chris Dicesare for developing a custom computer program for this study. Thank you to the National Institute for Occupational Safety and Health and all those involved with providing the funding for grant number 200-2015-M-87462. Without this funding, this research would never have been accomplished. Finally, I’d like to thank my family for their endless support throughout my career. Page 5 of 144 Table of Contents ABSTRACT .................................................................................................................................................. 2 ACKNOWLEDGMENT ............................................................................................................................... 5 1.0 INTRODUCTION .......................................................................................................................... 10 2.0 PURPOSE ....................................................................................................................................... 11 3.0 BACKGROUND ............................................................................................................................ 12 4.0 METHODS ..................................................................................................................................... 14 4.1 Background Information on the Present Study ..................................................................................... 14 4.2 Subjects ............................................................................................................................................. 14 4.3 Study Design ..................................................................................................................................... 15 4.3.1 Questionnaire / Screening .......................................................................................................... 15 4.3.2 Magnetic resonance imaging (MRI) .......................................................................................... 15 4.3.3 Static and Dynamic Balance Assessments ................................................................................. 17 4.4 Data Analysis .................................................................................................................................... 21 4.4.1 Phase Plane Analysis ................................................................................................................. 21 4.4.2 Sway Force Plate Independent Variables ................................................................................... 26 4.4.3 Gait Independent Variables ........................................................................................................ 27 4.4.4 Statistical Analysis Plan ............................................................................................................. 29 5.0 RESULTS ............................................................................................................................................. 34 5.1 Static and Dynamic fMRI Judgement Tasks ..................................................................................... 35 5.1.1 fMRI Judgement Pairwise Concordance .................................................................................... 35 5.1.2 fMRI Judgement Compared to Questionnaires .......................................................................... 40 5.2 Sway Analysis ................................................................................................................................... 41 5.2.1 Sway PSPSI Analysis................................................................................................................. 42 5.2.2 Sway Classification Analysis ..................................................................................................... 45 5.3 Gait Analysis ..................................................................................................................................... 47 5.3.1 Gait PSPSI Analysis ..................................................................................................................... 47 5.3.2 Gait Classification Analysis ......................................................................................................... 49 6.0 DISCUSSION ....................................................................................................................................... 53 6.1 Static and Dynamic fMRI Judgement Tasks ..................................................................................... 53 6.2 PSPSI Analysis ................................................................................................................................. 54 6.3 Sway Analysis ..................................................................................................................................