PURPOSE:The purpose of this study was to determine the affect of obesity on spirometry in patients who smoke.
METHODS:We analyzed all consecutive spirometries that met the ATS standards in male smokers tested at our VA Medical Center pulmonary function laboratory. We eliminated patients with confounding lung and cardiac diseases. We compared 142 tests in patients with a BMI ≤; 25 Kg/m2 (mean ± SD = 22.1 ± 2.1) with 133 in patients with a BMI ≥ 30 (34.7 ± 4.6) using an unpaired t-test for variables and χ2 for abnormal rates. The two groups are not different in smoking history (60.2 vs. 61.1 pack years) or age (59.3 vs. 57.1). Power analysis showed that at least 100 patients in each group are necessary to detect a 10% difference in spirometric indices and abnormality rates with P < 0.05, adjusted for 6 comparisons. Variables are expressed as percent of predicted ± SD, using the NHANES III equations appropriate for race and sex.
RESULTS:There is a statistically significant decrease in the forced vital capacities (FVC) in obese vs. normal weight patients (84% ± 17% vs. 90% ± 16%, P = 0.023). The forced expired volumes in one second (FEV1) are not different (69% ± 20% vs. 64% ± 21%, P = 0.2). This results in a greater FEV1/FVC ratio in obese patients (63% ± 13% vs. 54% ± 15%; P < 0.0001). Similarly, the number of abnormal tests is greater in obese patients for FVC (39% vs 23%, P = 0.023). The number of abnormal FEV1 is the same (64% vs. 69%; P = 0.94). This results in lower abnormality of the FEV1/FVC in obese patients (78% vs 50%; P = 0.001).
CONCLUSION:Obesity masks obstruction in male smokers. For the same degree of obstruction as measured by the FEV1, the FEV1/FVC is greater in obese patients because their FVC is reduced.
CLINICAL IMPLICATIONS:In obese male smokers, other tests may be necessary to detect obstruction.
DISCLOSURE:William Williams, No Financial Disclosure Information; No Product/Research Disclosure Information