Respiratory function in the very old and its impact on disability and mortality

Abstract

The aim of this PhD is to better understand the epidemiology of respiratory function in very old people and specifically examine the relationship between respiratory function and both cognitive function and disability in this age group. Data from the Newcastle 85+ study, a longitudinal cohort study of 85 year olds (born in 1921) were used in this thesis. Very few studies have investigated lung function and especially its impact on disability and mortality in the very old, and the unique point of this study was the multiple measurements of three lung function parameters: FEV1, FVC and PEF, between the ages of 85 and 88 years. Four sub-studies constituted the substantive results chapters of this thesis. The first sub-study described the prevalence of respiratory disease in the very old and the applicability of indicators of poor lung function and their cutpoints in this age group. The second sub-study explored the predictive ability of lung function for subsequent survival. The third sub-study quantified how lung function changes with further ageing in 85 year olds. The fourth sub-study examined the relationship between lung function and disability, particularly the direction of causality, and the potential mediating role of cognitive function. In the very old significant differences were observed between physician-diagnosed COPD and the obstructive classification of spirometry using the Global Initiative for Chronic Obstructive Lung Disease (GOLD) and Global lung initiative (GLI) prediction models. Lung function was predictive of mortality in women only. When investigating lung function trajectories of change, smoking and cognitive impairment were associated with lower FEV1. Bidirectional causality between lung function and disability revealed that higher FEV1 at ages 85, 86.5 and 88 was associated with lower disability at subsequent follow-ups (ages 86.5, 88 and 90) whilst higher disability scores at age 85 were associated with lower FEV1 at age 86.5.