Relative, Absolute Lung Function Change and Risk Factors in Older Patients

Current smoking habits, elevated C-reactive protein (CRP), older age, and low educational level all contribute to forced expiratory volume in 1 second (FEV₁) and forced expiratory vital capacity (FVC) decline, according to a study published in European Respiratory Journal.

Researchers assessed absolute and relative change in FEV1 and FVC in a population-based geriatric sample (N=3736; 60 to 102 years) with a repeated measurements model that was adjusted for age, alcohol consumption, body mass index, CRP, coronary heart disease, diabetes, educational level, heart failure, hypertension, occupation, sex, and smoking habits. Participants completed 1 to 5 spirometries over 13.5 years of follow-up. Lung volumes, FEV₁Q, Global Lung Function Initiative 2012 (GLI-2012), and National Health and Nutritional Examination Survey III Z-scores (NHANES III Z) were gathered from 6932 spirometries.

Adjusted absolute change per year was –56.2 mL (–73.6 to –38.8) for FVC and –51.7 mL (–63.7 to –39.9) for FEV1, whereas adjusted relative change per year was –2.46% (–3.07 to –1.85) for FVC and –2.97% (–3.53 to –2.40) for FEV₁. Confirmed risk factors for increased relative decline in FVC and FEV₁ were older age, current smoking habits, female sex, CRP (nonsignificant for FEV₁; P =.057), and low education level. Confirmed risk factors for increased absolute decline were low education level for FVC and being a current smoker and male sex for FEV₁. Relative change showed significant correlation with clinically relevant functional status markers and may be superior in risk factor analysis compared with absolute change.

Study limitations included the age of participants since longitudinal studies of geriatric patients can have a higher dropout rate due to morbidity and death. After adjusting for age and sex, having an FEV₁ and FVC GLI Z-score below the lower limit of normal, being a current smoker, and lower functional status were significantly associated with a failure to achieve >2 acceptable spirograms.

The investigators concluded, “For a potential risk factor having a strong influence on initial volume (such as female sex) it is crucial to choose an appropriate model as outcomes of different models may be diametrically opposite. We found some support for the relevance of relative change when studying risk factors of lung function decline. We also found that NHANES III may offer better reference equations for elderly compared to GLI-2012. These findings should be replicated and further investigated.”

Reference

Luoto J, Pihlsgård M, Wollmer P, Elmståhl S. Relative and absolute lung function change in a general population aged 60-102 years [published online December 21, 2018]. Eur Respir J. doi:10.1183/13993003.01812-2017