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Please use this identifier to cite or link to this item: http://hdl.handle.net/1959.13/928178

Title
The study of health outcomes in aircraft maintenance personnel: sensory system dffects
Author/Creator
Guest, Maya
Institution
University of Newcastle. Faculty of Health, School of Medicine and Public Health
Description
Research Doctorate - Doctor of Philosophy (PhD)
Description
Introduction: The effects of workplace exposure to neurotoxins on the central nervous system are well documented, however the effects on senses is an emerging area. This thesis has examined the senses: hearing, balance, touch and colour vision in a group of aircraft maintainers from the Royal Australian Air Force who undertook deseal/reseal fuel tank maintenance on F-111 aircraft compared to two different control groups. This exposed group used formulations containing neurotoxins in the fuel tank deseal/reseal process. Methods: Study population: The study population consisted of three groups: F-111 deseal/reseal exposed personnel, technical-trade comparisons to assess different base, same job and non-technical comparisons to assess same base, different job. The study utilised a mailed postal questionnaire and a series of clinical assessments. As military personnel, this study population met minimum physical fitness requirements on enlistment. Clinical assessment: Hearing was assessed by measuring hearing thresholds of each ear at eight frequencies from 500 to 8000 Hz using pure-tone audiometry. The percentage loss of hearing was calculated. Balance was assessed by measuring functional reach. Touch was assessed by measuring vibration perception thresholds at distal extremities using biothesiometry. Colour vision was assessed using the Ishihara test plates and the Lanthony D-15 Desaturated colour disc arrangement test. Those who failed the Ishihara test were excluded from the analysis. From the Lanthony colour disc arrangement test results the type of colour deficient vision was diagnosed, and Bowman’s colour confusion index was calculated. Other risk factors: In the postal questionnaire and during the clinical examination a number of other risk factors were assessed: anxiety and depression were assessed using the composite International Diagnosis Interview, Kessler Psychological distress scale, height, weight, and visual acuity (using Snellen chart). From the postal questionnaire information on general health and well-being, alcohol intake, smoking history, existence of tinnitus, doctor diagnosed diabetes, medications regularly used and a civilian job history were obtained. Other risk factors included in all statistical modeling included age, posting category, rank and location of clinical assessment. Statistical methods: Regression models were used to examine whether there was an association between F-111 fuel tank maintenance and sensory impairments, adjusting for possible confounders. In addition multiple linear regressions were also used to determine whether any association exists between the functional reach and the auditory thresholds at the eight measured frequencies in both ears. Graphical comparison was made of the hearing thresholds at all eight frequencies with the published ISO-7029 medians. Results: The study population consisted of 614 exposed personnel, 513 technical-trade comparisons and 403 non-technical comparisons (numbers in each analysis differ slightly). The percentage loss of hearing ranged from nil to 96 (median 1.5, quartiles 0.3, 5.5). A logistic regression model showed no statistically significant difference in percentage loss of hearing among the three exposure groups (exposed verses non-technical controls OR 1.1: 95%CI 0.7, 2.0 and exposed verses technical OR 0.9: 95% CI 0.6, 1.3). However, at all eight frequencies measured, all populations had lower than expected hearing thresholds based on published ISO-7029 medians. The linear regression model showed that functional reach was slightly better for the comparison groups than the deseal/reseal group with only one group being statistically significant; however the difference was not clinically significant. The model did show that functional reach decreases significantly with age, anxiety and depression, whereas it improves with height. A significant association was found between vestibular function, measured by functional reach, and auditory thresholds at 500 and 1000 Hz, which were influenced by anxiety. Over 26% of all study participants had chronic persistent decreased vibration perception threshold in the great toe. Statistically significant higher vibration perception threshold of the great toe was observed in the comparison groups; this remained significant when vibration perception threshold was dichotomized into normal and abnormal categories; however the effect was small and about ¼ the magnitude of diabetes. Age, height and diabetes were all significant and stronger predictors in most models. Colour confusion index results ranged from 1 to 2.8 (median 1.2, quartiles 1.1, 1.4) in the 2600 eyes tested. Forty five percent of all study participants had blue-yellow colour deficient vision in at least one eye which is consistent with environmental exposures. Logistic regression demonstrated statistically significant differences in colour confusion index category in the exposed group versus technical group (OR 1.7: 95% CI 1.3-2.0) and a blue-yellow confusion in the exposed group versus technical group (OR 1.4: 95% CI 1.1-1.7). Discussion: This study has examined the effects of the deseal/reseal exposures and aircraft maintenance on four senses: hearing, balance, touch and colour vision. The hearing analysis showed that while the study participants had high levels of hearing loss in comparison to the published ISO7029 medians we did not observe any difference between the three exposure groups. The analysis for balance did show a difference with one of the exposure groups; however the difference was too small to be clinically significant. The analysis for touch did show that one quarter of all study participants had chronic persistent increased vibration perception threshold in the great toe and the analysis for colour vision indicated reduced colour discrimination among the exposed subjects compared to the Richmond controls. These findings are relatively weak in determining the effect of the deseal/reseal exposures on these senses. However, the comparison with normative data that were available (hearing and vibration perception) did show that the study population as a whole have higher hearing thresholds and higher vibration perception thresholds. In the absence of normative data for colour vision we observed almost one third of all participants had an abnormal colour confusion index or a blue-yellow deficit. These finding would suggest that whilst the deseal/reseal exposures to ototoxins and neurotoxins were high, a Royal Australian Air Force effect is also being observed. This statement can be made with some confidence as all military personnel are required to be physically fit and pass a stringent medical before enlistment. Study strengths and weaknesses: a strength is the number of study participants; 1538 participants were examined for the general health and medical assessment making the SHOAMP study one of the largest in the examination of sensory neuropathy. Another is that all outcomes reported were directly measured in the health examination; no self-reported data has been used. One caveat is the study was carried out retrospectively without exposure data for the substances used in the deseal/reseal programs. Conclusion: This thesis has compared a series of sensory outcomes in personnel involved in F-111 DSRS activities with two contemporaneous comparisons groups. It shows non-specific decrease in hearing due to Air Force wide exposures, likely noise, but it does show a specific decrease in colour vision probably due to deseal/reseal exposures.
Relation
University of Newcastle Research Higher Degree Thesis
Date
2011
Keyword(s)
aircraft maintenance;  F-111s;  deseal/reseal;  colour vision;  hearing;  vibration perception;  balance
Resource Type
thesis
Rights
Copyright 2011 Maya Guest
Identifier
http://hdl.handle.net/1959.13/928178
Language
eng
 
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"The study of health outcomes in aircraft maintenance personnel: sensory system dffects"
 
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