Chronic obstructive pulmonary disease : clinical phenotyping, mortality and causes of death

Abstract: BackgroundChronic obstructive pulmonary disease (COPD) is common. The estimated prevalence is about 10% among adults, but varies largely dependent on the major risk factors age and smoking. Under-diagnosis of COPD is substantial and is related to disease severity. Thus, subjects with mild to moderate COPD are underrepresented in medical registers among health care providers as well as in national registers. Post- bronchodilator (BD) spirometry is mandatory for the diagnosis of COPD, but not sufficient to assess and manage COPD. Phenotyping based on spirometry and clinical manifestations can make it easier to apply individual assessment of subjects with COPD. COPD is a systemic disease with pulmonary and extra-pulmonary manifestations and comorbidities are common. Comorbidities most probably contribute to the observed increased mortality among subjects with COPD, however, the impact of comorbidities on mortality and causes of death among subjects with mild to moderate COPD is unclear. Furthermore, there seems to be sex-dependent differences with regard to susceptibility to risk factors, clinical manifestation and outcomes.Aim The overall aim of this thesis was to identify and characterize clinical relevant COPD phenotypes in population-based studies, using spirometry together with clinical characteristics such as respiratory symptoms, exacerbations, and comorbidities, and their impact on mortality and further, also cause of death.Methods This thesis is based on data from the Obstructive Lung Disease in Northern Sweden (OLIN) COPD study. The study population was recruited in the years 2002-2004, when all 993 individuals with (FEV1/VC<0.70) were identified after examinations of population-based cohorts, together with age- and sex-matched non-obstructive referents (n=in total 1,986). In this thesis, cross-sectional data from recruitment were used together with mortality data from the Swedish Tax Agency from the date of recruitment in 2002-2004 and onwards. Data on cause of death was collected from the Swedish National Board for Health and Welfare register for all deaths until 31 December 2015. Spirometry was used to identify the following spirometric groups, in paper I: Non-COPD (FEV1/VC≥0.70); COPD (pre- BD FEV1/VC<0.70); in paper II: Non- obstructive (FEV1/VC≥0.70), Pre- not post-BD obstructive (pre- not post-BD FEV1/VC<0.70); COPD (post-BD FEV1/VC<0.70); In paper III: Normal Lung Function (NLF, FEV1/VC≥0.7 & FVC≥80% predicted), COPD (post BD FEV1/VC<0.70) and Lower Limit of Normal COPD (LLN-COPD, the LLN criterion applied among those with COPD); in paper IV: NLF and COPD defined as in paper III, and Restrictive Spirometric pattern (RSP, FEV1/VC≥0.70 & FVC<80% predicted). The OLIN-COPD study and collection of data on causes of death were approved by the regional ethical committee at Umeå University.ResultsPaper I: Subjects with COPD had more productive cough than non-COPD, and men more than women. Productive cough increased the risk for exacerbations in COPD and non-COPD and productive cough was associated with worse survival in both groups. In adjusted models (HR;95%CI) the increased risk for death associated with productive cough among those with COPD persisted (1.48;1.13-1.94) when compared with non-COPD without productive cough, significantly so also among men with COPD (1.63;1.17-2.26), but not among women (1.23;0.76-1.99).Paper-II: Pre-BD spirometry misclassified every fourth subject as having COPD. Subjects with pre- but not post-BD obstruction were similar to subjects with COPD regarding reported ‘any respiratory symptoms’, asthma before the age of 40, exacerbations, and comorbidities. The cumulative mortality among subjects with pre- not post-BD obstruction was similar to among subjects in the non-obstructive group, still, the survival was better than among those with COPD. The increased risk for death for COPD persisted also in an adjusted model (1.24; 1.04-1.49) when compared with the non-obstructive group, and the pattern was similar among men and women (1.27; 1.00-1.60 and1.24; 0.92-1.13).Paper III: Men with COPD had more CVD and DM compared to women, while anxiety/depression (A/D) was more common among women than men in all spirometric groups. Men had a higher cumulative mortality than women in all groups. However, CVD seemed to have a greater impact on mortality among women than men, while anxiety/depression increased the risk for death similarly in both sexes. The use of the LLN criterion did not change the observed pattern.Paper IV: CVD was the most common cause of death in all spirometric groups, NLF, RSP and COPD, followed by cancer. Those with COPD and RSP had a similar and higher cumulative mortality than those with NLF. RSP and COPD had an increased risk for CVD death and respiratory death, independent of age, sex, smoking habits and BMI-category, however, the increased risk for CVD death did not reach statistical significance in RSP. In all the groups, the risk for deaths due to cancer was similar, however, lung cancer was more common in COPD than in NLF and RSP. The pattern was fairly similar among men and women. Conclusions Simple diagnostic procedures like history of respiratory symptoms, exacerbations, and comorbidity can, together with spirometry, contribute with important clinical classification of prognostic importance. Productive cough increased the risk for exacerbations in both COPD and non-COPD. The highest risk for exacerbations and death was observed among subjects with COPD and productive cough. It was impossible to distinguish COPD from those with pre- not post-BD obstruction based on the history of respiratory symptoms, asthma, exacerbations and comorbidities. Still, COPD was associated with an increased risk for death while pre- not post-BD obstruction had better survival than COPD but similar as non-obstructive. There were sex-dependent differences regarding comorbidities and mortality. CVD was less common among women but had a greater impact on mortality compared to among men while A/D, less common among men, increased the risk for death similarly in both sexes. CVD and cancer were the most common causes of death in all spirometric groups. RSP had a similar and higher mortality as COPD when compared with NLF. The risk for cancer-related death was similar in all groups, while the results indicated that COPD and RSP had an increased risk for CVD and respiratory death.