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. 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 (FEV₁), forced vital capacity (FVC), and FEV₁/FVC. Results: Adjusting 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. Conclusions: Smoking, 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.