Determinants of Forced Expiratory Volume in 1 Second (FEV1), Forced Vital Capacity (FVC), and FEV1/FVC in Chronic Spinal Cord Injury

Jain NB, Brown R, Tun CG, Gagnon D, Garshick E. Determinants of forced expiratory volume in 1 second (FEV1), forced vital capacity (FVC), and FEV1/FVC in chronic spinal cord injury.ObjectiveTo assess factors that influence pulmonary function, because respiratory system dysfunction is common in chronic spinal cord injury (SCI).DesignCross-sectional cohort study.SettingVeterans Affairs Boston SCI service and the community.ParticipantsBetween 1994 and 2003, 339 white men with chronic SCI completed a respiratory questionnaire and underwent spirometry.InterventionsNot applicable.Main Outcome MeasuresForced expiratory volume in 1 second (FEV1), forced vital capacity (FVC), and FEV1/FVC.ResultsAdjusting for SCI level and completeness, FEV1 (–21.0mL/y; 95% confidence interval [CI], –26.3 to –15.7mL/y) and FVC (–17.2mL/y; 95% CI, –23.7 to –10.8mL/y) declined with age. Lifetime cigarette use was also associated with a decrease in FEV1 (–3.8mL/pack-year; 95% CI, –6.5 to –1.1mL/pack-year), and persistent wheeze and elevated body mass index were associated with a lower FEV1/FVC. A greater maximal inspiratory pressure (MIP) was associated with a greater FEV1 and FVC. FEV1 significantly decreased with injury duration (–6.1mL/y; 95% CI, –11.7 to –0.6mL/y), with the greatest decrement in the most neurologically impaired. The most neurologically impaired also had a greater FEV1/FVC, and their FEV1 and FVC were less affected by age and smoking.ConclusionsSmoking, persistent wheeze, obesity, and MIP, in addition to SCI level and completeness, were significant determinants of pulmonary function. In SCI, FEV1, FVC, and FEV1/FVC may be less sensitive to factors associated with change in airway size and not reliably detect the severity of airflow obstruction.