Effect of Weight Reduction on Respiratory Function and Airway Reactivity in Obese Women

Shawn D. Aaron, MD, MSc; Dean Fergusson, PhD; Robert Dent, MD; Yue Chen, PhD; Katherine L. Vandemheen, BScN; Robert E. Dales, MD, MSc


CHEST. 2004;125(6) 

In This Article

Materials and Methods

We enrolled consecutive female subjects with a BMI > 30 kg/m2 who had entered the Ottawa Hospital Weight Loss Clinic and consented to participate in the study. We enrolled an approximately equal number of patients during the summer and winter months to try to control for potential seasonal changes in bronchial responsiveness. Patients were excluded if they had been receiving oral corticosteroids on a regular basis, if they were pregnant, if they had a history of myocardial infarction or stroke within the previous 3 months, or if they had a known history of aortic aneurysm. The study was approved by the Ottawa Hospital Research Ethics Board, and all subjects signed informed consent forms.

Patients were placed on a regimen of three liquid meal replacement supplements per day, which delivered 300 kilocalories (kcal) per meal (40% of calories from protein, 30% of calories from carbohydrates, and 30% of calories from fat). Those with severe obesity (ie, initial BMI, > 35 kg/m2) were enrolled into a long program consisting of a diet of 900 kcal per day that continued for 12 weeks. Patients with less severe obesity (ie, mean initial BMI, 30 to 35 kg/m2) were enrolled into a shorter program consisting of the same diet of 900 kcal per d diet that continued for 6 weeks.[7] In all cases, regular counseling, a restricted calorie diet, and follow-up of enrolled patients occurred on a weekly basis for at least 6 months.

Patients were assessed in a series of three paired study visits, as follows: before beginning the weight reduction program; at 3 months after enrolling in the weight reduction program; and at 6 months after enrolling in the weight reduction program. At the first visit, they underwent prebronchodilator and postbronchodilator spirometric testing, and measurements of plethysmographic lung volume. Measurements were performed after bronchodilator therapy had been withheld for at least 12 h and were obtained by certified pulmonary technologists according to American Thoracic Society criteria. At a second visit the same week, a standardized bronchial challenge test was performed.[8,9] Increasing concentrations of inhaled methacholine were administered, and spirometry was performed after each inhalation according to published protocols.[8,9] The tests were stopped once the FEV1 had fallen 20% from baseline, or after a concentration of 32 mg/mL had been administered. All study visits were made when patients were clinically stable and were receiving their usual doses of anti-inflammatory asthma medications.

Symptoms and disease-specific quality of life were assessed using the St. George Respiratory Questionnaire (SGRQ) at baseline and every 3 months for the duration of the 6-month study.[10] This questionnaire includes the following three domains: symptoms (ie, distress caused by specific respiratory symptoms); activity (ie, physical activities that cause or are limited by breathlessness); and impact (ie, social and psychological effects of the respiratory disease). A decrease in the score indicates an improvement in health status. A total change of –4 in the SGRQ score is considered to be clinically significant.[10,11] At each visit, respiratory symptoms, medication use, and changes in exposure to indoor, outdoor, and work-related allergens, tobacco smoke, diet, and exercise were recorded.

Baseline characteristics were evaluated for all patients using measures of central tendency and dispersion. Pearson correlation coefficients were calculated to describe the relationship between weight change and unadjusted changes in FEV1, FVC, provocative concentration of a substance causing a 20% fall in FEV1 (PC20), and SGRQ total score.

Analyses involving all 58 patients comparing relative weight change and the effect on absolute changes in lung function (ie, FEV1, FVC, and total lung capacity [TLC]), airway reactivity (ie, PC20), and quality of life (ie, SGRQ) were calculated using linear regression models. Absolute changes in FEV1, FVC, and TLC were adjusted for age and height. Changes in airway reactivity are reported as the log2 change in methacholine responsiveness, and were adjusted for history of asthma, atopy, and smoking status, since these patient characteristics are known to influence methacholine responsiveness. Regression coefficients were multiplied by 10 to represent a 10% relative change in weight loss.

Our previous observations of the patients who entered into the Ottawa Hospital Weight Loss Clinic program suggested that one quarter of patients fail to lose at least 10% of their pretreatment weight. Based on this observation, the study protocol stipulated that we would compare those patients in the lowest quartile of relative weight reduction to those who were in the upper three quartiles at the end of the 6-month observation period. Therefore, additional analyses were performed for the 50 patients who completed the 6 months of follow-up, dividing these patients into the lowest quartile and the upper three quartiles of relative weight change. All outcome measures are reported as average absolute changes with 95% confidence intervals.


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