Relationship of dyspnea to respiratory drive and pulmonary function tests in obese patients before and after weight loss

Background: Dyspnea is a common complaint in obese patients, who also frequently have abnormal pulmonary function test (PFT) results without evidence of lung disease. We studied the relationship between dyspnea, PFT results, and respiratory drive in morbidly obese patients before and after weight loss. Method: Twenty-eight obese patients underwent PFTs including spirometry, lung volume measurements, and ventilatory drive assessment using the carbon dioxide rebreathing technique. The score of the dyspnea portion of the Chronic Respiratory Disease Questionnaire (CRQ) was used to assess dyspnea. CRQ and respiratory drive measurements were repeated in 10 patients after induced weight loss by gastroplasty Results: Mean +/- SD body mass index (BMI) prior to surgery was 47 +/- 6.5 kg/m(2). Patients were then classified into two groups: group 1, mild-to-moderate dyspnea (dyspnea score > 4); and group 2, severe dyspnea (dyspnea score < 4). Group 2 had higher respiratory drive parameters and significantly lower lung volumes compared to group 1. After gastroplasty, there were significant reductions in BMI (p = 0.000), dyspnea score (p = 0.000), occlusion pressure 100 ms after the start of inspiration (P-100) at end-tidal carbon dioxide (ETCO2) of 60 mm Hg (p = 0.011), minute ventilation (VE) at ETCO2 of 60 mm Hg, and VE slope (0.017). P-100 slope was reduced, but it did not reach statistical significance. Conclusion: The degree of dyspnea commonly observed in obese patients can be explained, in part, by increased ventilatory drive and reduced static lung volumes. Gastroplasty results in a significant reduction in BMI and respiratory drive measurements as well as significant improvement in dyspnea.