The impacts of deployment related exposures on respiratory health of Australian Defence Force members

Abstract

BACKGROUND Recent evidence from international literature suggests an elevated prevalence of adverse respiratory conditions among military personnel during and following deployment to the Middle East. Australian Defence Force (ADF) members may also be at risk for developing respiratory conditions. However, there is a paucity of prospective studies regarding the level of respiratory distress and identification of potential factors leading to adverse respiratory outcomes among ADF members post- deployment. AIMS AND HYPOTHESES The aims of this thesis are: 1) To investigate if, similar to the reported international literature, there is an increase in subjective respiratory symptoms (self-reported respiratory symptom measured using a medical and respiratory questionnaire) of ADF members from pre- to postdeployment to the MEAO between 2010 and 2012 and whether these are accompanied by any changes in objective function (FEV1/FVC lung function measured by spirometry), possibly at a sub-clinical level. (Chapter 3 presents and discusses this topic). 2) To examine the predictors of adverse respiratory outcomes among this cohort in the context of combat environmental and psychological trauma exposures (Chapter 4 provides detailed investigation of predictors of adverse respiratory outcomes). In light of findings from the existing literature, it was hypothesised that there would be an observable decline in both objective and subjective respiratory function of contemporary ADF members from pre-to post-deployment to MEAO between 2010 and 2012. Further, it was also postulated that environmental and psychological trauma exposures would independently and combined contribute to changes in self-reported respiratory symptoms and objective respiratory measures in this cohort of ADF members. METHODS Data from the MEAO prospective study were analysed to investigate the effect of deployment related exposures on adverse respiratory outcomes. From a total sample of 3074 who were deployed to the MEAO between 2010 and 2012, a specific subsample was utilised in this thesis, including the 202 ADF members in combat roles with complete reliable spirometry results at pre-and post-deployment, who also completed self- reported questionnaires. Self-reported respiratory symptoms, and objective measures of respiratory function (Forced Expiratory Volume in one second (FEV1), Forced Vital Capacity (FVC), and FEV1/FVC ratio) were assessed at both pre and post-deployment. Self-reported environmental and psychological trauma exposures incurred during deployment were assessed at post-deployment. RESULTS While the majority of individuals were still within the normal range of objective respiratory function, analyses of both objective and subjective data showed that there were significant decreases in both objective and self-reported respiratory function following deployment. In addition, the decline in objective function was found to be significantly associated with selfreported respiratory symptoms. The results showed that environmental and psychological trauma exposures experienced on deployment were independently associated with adverse respiratory outcomes on both objective and self-report measures. Importantly there was also a significant interaction, with the association between environmental exposures and both objective and self-reported respiratory measures stronger under conditions of high compared to low psychological trauma exposure. CONCLUSIONS The findings of this study support the hypothesis that there would be a decline in objective and subjective respiratory function of ADF members following deployment to the MEAO. Furthermore, environmental and psychological trauma exposures experienced on deployment both contributed to these changes. The results suggest that psychological trauma may increase vulnerability to the effects of environmental exposures on respiratory outcomes. One possible mechanism underpinning the association between psychological stress and reduced respiratory function could be increased levels of systemic inflammatory mediators, leading to increased susceptibility to environmental exposures, via a compromised immune system. Another possibility is that the cumulative burden of all exposure types impacts respiratory function. However, it is also important to consider that it is likely that environmental and psychological exposures were somewhat confounded due to the nature of the deployed environment; environmental exposures such as being exposed to blast or toxins is likely to have carried a burden of psychological stress. While the aetiology behind the findings showing that psychological trauma exposures are associated with physical health changes remains unclear, the effect of psychological factors on the relationship between environmental exposures and respiratory function cannot be excluded as a potential contributing factor, suggesting that strategies should be developed and implemented to reduce the effects of these exposures on military personnel during deployment. A decrement in lung function below 70% is quite considerable. A recommendation could be to detect possible adverse respiratory health at an early stage to prevent long-term respiratory disease, and to recommend proactive interventions for prevention.