Using the methacholine challenge to determine how psychological mechanisms impact asthma symptom perception and quality of life

Abstract

The first chapter of this thesis reviews the literature exploring the association between anxiety and asthma, and the effect this has had on potential outcomes. The following outcomes are affected by the relationship: quality of life, control, symptom perception, dyspnoea, lung function, and healthcare utilisation. 26 studies were identified after searching four distinct specialist databases of publications. Quality of life and control was reduced in asthmatics who reported higher symptoms of anxiety. Reduction in dyspnea (or breathlessness) and symptom perception was lower in anxious groups and not associated with lung function. Finally, the articles highlighted the link between anxious asthmatic and increased healthcare utilisation. Anxiety plausibly has a role in misinterpretation of symptoms, affecting control, subsequent quality of life, and healthcare use. Limitations of the reviewed studies include a lack of consistency in measuring anxiety and outcomes, a small number of longitudinal studies, and finally a lack of exploration of mechanisms underpinning the association. The empirical paper explored how psychological mechanisms impact on asthmatics perception of breathlessness, quality of life, and control. Anxiety in asthma has been associated with perception of breathlessness, a cornerstone of asthma management. The experimental study used a Methacholine Test (MCT) to reduce lung function to 80% to induce bronchoconstriction to explore the effect of reduced lung function on anxiety, breathlessness, asthma quality of life, asthma control and association with attentional resources. Attentional bias was measured by a computer task (Attentional Network Test, ANT) and a self-report (Attention Control Scale, ACS). 31 participants were recruited for the study. Changes in breathlessness were noted across conditions, independent of lung function. Breathlessness was associated with anxiety and not with Asthma Quality of Life (AQLQ) or their asthma control. In a blockwise regression analysis, anxiety was a significant predictor of quality of life and control of asthma. Perceived breathlessness or anxiety was not significantly associated with attention as measured by ANT, though anxiety was associated with self-reported measures of attentional shift and focus. Subsequently, increased breathlessness during bronchoconstriction revealed a decrease in shifting attention. Attention could be a mechanism to target in improving asthma care; however, further research is needed. Limitations, clinical implications, and future directions for research are discussed.