Grading the severity of obstruction in patients with chronic obstructive pulmonary disease and morbid obesity

To evaluate the severity of airway obstruction in patients affected by chronic obstructive pulmonary disease (COPD) in the presence of concomitant restriction due to morbid obesity.

Lung function test, six-minute walking distance (6MWD) test, body mass index measurement (BMI), and determination of dyspnoea using the Modified Medical Research Council Dyspnoea Scale (MMRC) were performed on each patient referred to our department according to their individual respiratory diagnosis or symptoms. Analysis was performed on smokers or ex-smokers patients, with both dyspnoea and chronic productive cough, showing non fully reversible airflow obstruction, with normal-weight (NW: BMI 22 to 24 kg/m2) or morbid-obesity (MO: BMI > or = 40 kg/m2).

In 33 COPD patients, spirometric data differ between NW and MO only in fixed FEV1/FVC ratio (50 +/- 9 and 62 +/- 7, respectively; p = 0.0001) and FEV1/SVC % of predicted (57 +/- 15 and 71 +/- 11, respectively; p = 0.005). Furthermore, SVC was found to exceed FVC only in NW (2.82 +/- 0.7 L and 2.08 +/- 0.9 L, respectively; p = 0.03). NW and MO differ significantly also in MMRC (3.4 +/- 0.9 vs 2.4 +/- 1, respectively; p = 0.004), 6MWD in metres (226 +/- 100 and 331 +/-110, respectively, p = 0.007), 6MWD as % predicted (49 +/- 22 and 81 +/- 23, respectively; p = 0.0003), and BODE index (5.8 +/- 2 and 3.6 +/- 2, respectively; p = 0.003).

There is a significant overgrading of obstruction in morbidly obese patients affected by COPD. Therefore, we suggest that an alternative grading system be used for patients with mixed ventilatory dysfunction.