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Relationship of Dyspnea to Respiratory Drive and Pulmonary Function Tests in Obese Patients Before and After Weight Loss^*

^* From the Pulmonary and Critical Care Division, Departments of Medicine (Drs. El-Gamal, Khayat, and Unterborn) and Surgery (Dr. Shikora), Tufts-New England Medical Center, Boston, MA.

Correspondence to: John N. Unterborn, MD, Pulmonary and Critical Care Division, Department of Medicine, Tufts-New England Medical Center, 750 Washington St, Boston, MA; e-mail: junterborn{at}tufts-nemc.org

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/m². 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 (P₁₀₀) at end-tidal carbon dioxide (ETCO₂) of 60 mm Hg (p = 0.011), minute ventilation (E) at ETCO₂ of 60 mm Hg, and E slope (0.017). P₁₀₀ 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.

Key Words: dyspnea • obesity • pulmonary function tests

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