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

Abstract

Jain NB, Brown R, Tun CG, Gagnon D, Garshick E. Determinants of forced expiratory volume in 1 second (FEV 1), forced vital capacity (FVC), and FEV 1/FVC in chronic spinal cord injury. Objective To assess factors that influence pulmonary function, because respiratory system dysfunction is common in chronic spinal cord injury (SCI). Design Cross-sectional cohort study. Setting Veterans Affairs Boston SCI service and the community. Participants Between 1994 and 2003, 339 white men with chronic SCI completed a respiratory questionnaire and underwent spirometry. Interventions Not applicable. Main Outcome Measures Forced expiratory volume in 1 second (FEV 1), forced vital capacity (FVC), and FEV 1/FVC. Results Adjusting for SCI level and completeness, FEV 1 (–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 FEV 1 (–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 FEV 1/FVC. A greater maximal inspiratory pressure (MIP) was associated with a greater FEV 1 and FVC. FEV 1 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 FEV 1/FVC, and their FEV 1 and FVC were less affected by age and smoking. Conclusions Smoking, persistent wheeze, obesity, and MIP, in addition to SCI level and completeness, were significant determinants of pulmonary function. In SCI, FEV 1, FVC, and FEV 1/FVC may be less sensitive to factors associated with change in airway size and not reliably detect the severity of airflow obstruction.