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 -15.7 mL/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 -1.1 mL/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.