Background Abnormal lung volumes that reflect air trapping are common in COPD. However, their significance in smokers with preserved spirometry (normal FEV1 to FVC ratio) is unclear.
Methods Using the Veterans Administration Informatics and Computing Infrastructure database, we identified 7479 patients at risk for COPD (ever smokers >40 years of age without restrictive lung disease) who had preserved spirometry and concomitant lung volume measurements, and examined their subsequent health records for clinical diagnoses of COPD, healthcare utilisation, follow-up spirometry and mortality.
Results Air trapping was prevalent, with 31% of patients having residual volume to total lung capacity ratio (RV:TLC) greater than the upper limit of normal (ULN). RV:TLC varied widely from 14% to 77% (51% to 204% of predicted) across the normal ranges of FEV1:FVC and FEV1. Patients with RV:TLC greater than the ULN were more likely to receive subsequent clinical diagnoses of COPD (HR (95% CI)=1.55 (1.42 to 1.70), p<0.001) and had higher all-cause mortality (HR (95% CI)=1.41 (1.29 to 1.54), p<0.001). They had higher rates of respiratory medication prescriptions and hospital and intensive care unit admissions. Other air trapping and static hyperinflation indices showed similar associations with health outcomes. Additionally, high-normal RV:TLC was associated with intermediate adverse health outcomes compared with low-normal and abnormal RV:TLC. Abnormal RV:TLC predicted higher likelihood of progression to spirometric COPD (OR (95% CI)=1.30 (1.03 to 1.65), p=0.027).
Conclusion In this study of the Veterans Affairs electronic health records, air trapping was common in smokers with preserved spirometry and predicted adverse respiratory outcomes and progression to overt COPD.
- copd epidemiology
- lung physiology
- respiratory measurement
- copd ÀÜ mechanisms
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SZ and AT contributed equally.
Contributors MA conceived and designed the study. MA, BB and SZ developed the study protocols. SZ, BB, BG, JJ and MA collected the data. SZ, MA, AT, BB and JJ analysed and interpreted the data. MA, AT, SZ, BB and JJ prepared the manuscript. MA and BB obtained funding.
Funding This work was supported by the Flight Attendant Medical Research Institute (MA) and Radboud University School of Medicine Scholarship (BB).
Competing interests None declared.
Patient consent Not required.
Ethics approval The University of California San Francisco Institutional Review Board and the Veterans Health Administration Research and Development Committee approved this study.
Provenance and peer review Not commissioned; externally peer reviewed.
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