Low Inspiratory Capacity to Total Lung Capacity Ratio Is a Risk Factor for Chronic Obstructive Pulmonary Disease Exacerbation

Introduction: Air trapping because of chronic obstructive pulmonary disease (COPD) leads to a reduction in inspiratory capacity/total lung capacity (IC/TLC) ratio. We hypothesize that COPD patients with a low IC/TLC ratio suffer more frequent COPD exacerbations. Methods: Retrospective cohort study of patients with COPD, aged 30 years or older with forced expiratory volume in 1 second <70% predicted and forced expiratory volume in 1 second/forced expiratory volume (FEV1/FVC) ratio <70% treated in our ambulatory care clinic for 3 years (2003-2006). Patients were divided in 2 groups, either IC/TLC ratio less than or greater than 25%. Results: Charts of 350 patients with COPD were reviewed. Of the 77 patients who met inclusion criteria, 28 patients (20 women and 8 men) had IC/TLC ratio <25% (low group) and 49 patients (25 women and 24 men) had IC/TLC ratio >25% (high group). Average number of exacerbations per person in the low group was 3.5 (0-10), significantly higher than in the high group, which was 2.2 (0-10; P = 0.01). Visits for COPD exacerbations were analyzed based on treatment site namely, office, emergency room (ER), and hospital. The per person office visits were 1.96 (0-10) in the low group and 0.80 (0-3) in the high group (P = 0.002). ER visits were similar, 0.57 (0-3) in the low group and 0.38 (0-3) in the high group (P = 0.15), as were hospital visits, 0.96 (0-8) in the low group and 1.06 (0-5) in the high group (P = 0.81). Conclusion: COPD patients in the low group experienced significantly more unscheduled office visits because of exacerbations, suggesting they need early identification and closely monitored therapy.