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

Disclosures

CHEST. 2004;125(6) 

In This Article

Results

Fifty-eight patients were enrolled in the study, and completed baseline and 3-month assessments. Eight patients withdrew from the study before completing their 6-month follow-up assessment. The mean (± SD) age of the patients was 44 ± 13 years. Twenty-four of the 58 patients (41%) had a history of physician-diagnosed asthma ( Table 1 ), and 21 patients (36%) were receiving medication for asthma at time of enrollment. The mean BMI of the patients entering into the study was 43.1 ± 8.8 kg/m2, and the mean body weight was 115 ± 26 kg. The 50 patients who completed the study lost an average of 20.0 kg over the 6-month study period (range, 0 to 35 kg), or 17.4% of their pretreatment weight.

Patients in the lowest quartile of relative weight reduction lost a mean of 8.0 ± 4.5% of their pretreatment weight (range, 0 to 12% weight loss over 6 months), and patients in the upper three quartiles lost a mean of 18.8 ± 4.9% of their pretreatment weight (range, 13 to 31%). There were no significant differences at baseline between these two groups in age, smoking status, initial BMI, or the proportion of those who had atopy or asthma ( Table 1 ).

None of the enrolled patients reported experiencing any difficulties with their asthma necessitating urgent visits to physicians or to the emergency department during the 6-month study period. Similarly, none of them reported any changes to their maintenance asthma medications during the 6-month study period.

For the entire group of 58 patients, there was a significant correlation between weight loss and unadjusted changes in the FEV1 (r = 0.29; p = 0.040). The association between weight loss and unadjusted changes in the FVC was similar, although not quite statistically significant (r = 0.27; p = 0.057) [Fig 1]. However, there was no significant correlation between weight loss and changes in airway responsiveness (r = 0.19; p = 0.203) [Fig 2].

Correlation between relative weight loss and changes in lung function.

Lack of correlation between relative weight loss and changes in airway reactivity.

For every 10% relative loss of pretreatment weight, the FVC (adjusted for age and height) improved by 92 mL (p = 0.05) and the FEV1 (adjusted for age and height) improved by 73 mL (p = 0.04). The effect of weight loss on the change in methacholine responsiveness was not significant. For every 10% relative loss of weight the log2 change in 20 (adjusted for asthma, atopy, and smoking status) improved by 0.53, which is equal to half a doubling dilution of methacholine (p = 0.23). Adjusting the change in PC20 for changes in lung volume (ie, TLC) did not influence the result (improvement in PC20, 0.27; p = 0.58).

A subgroup analysis of the 24 patients who had asthma did not show any improvement in PC20 with weight loss. In these patients, for every 10% relative loss of weight the log2 change in PC20 improved by only 0.19 (ie, one fifth of a doubling dilution; p = 0.66).

Fifty patients completed the entire 6-month follow-up, and they were divided into quartiles of relative weight loss. Patients in the upper three quartiles who lost ≥ 13% of their relative body weight demonstrated a significant 6-month improvement in FEV1 relative to those in the lowest quartile who lost < 13% of their initial body weight (mean improvement in FEV1, 0.14 ± 0.17 L vs –0.01 ± 0.15 L, respectively; p = 0.01). A similar improvement was seen for FVC changes (mean improvement in FVC, 0.21 ± 0.22 L vs 0.04 ± 0.22 L, respectively; p = 0.02) and TLC changes (mean improvement in TLC, 0.21 ± 0.43 L vs ± 0.10 ± 0.56 L, respectively; p = 0.05) for those who successfully lost weight compared to those who did not ( Table 2 ).

The average absolute change in methacholine responsiveness was not significantly different in those patients in the upper three quartiles who lost ≤ 13% of their relative body weight relative to those in the lowest quartile who lost < 13% of their initial body weight. The mean absolute change in log2 methacholine responsiveness was 0.18 ± 1.99 (ie, a positive change by one fifth of a doubling dilution) in those who lost weight compared to –0.23 ± 1.19 (ie, negative change by one fifth of a doubling dilution) in those who did not lose weight (p = 0.57 for the comparison between the two groups) [ Table 2 ].

Patients enrolled in the weight loss program experienced a significant improvement in their disease-specific quality of life, as measured by the SGRQ instrument. The largest changes seen were in the activity domain of the SGRQ, but all domains improved significantly (Fig 3). There was no correlation seen between relative weight change and change in the total SGRQ score over 6 months (r = –0.12; p = 0.44). Patients in the lowest quartile of relative weight reduction experienced similar 6-month improvements in total SGRQ score (change in total SGRQ score, –11.8 ± 13.1 U) compared to patients in the upper three quartiles who lost more weight (change in total SGRQ score, –8.7 ± 10.5 U; p = 0.42) [ Table 2 ].

Changes in respiratory health status for the patients who completed the 6-month weight-loss program. All domains of the SGRQ improved significantly (p < 0.05 for all domains). (Black square) = activity domain of the SGRQ; (black diamond) = symptoms domain of the SGRQ; (black triangle)= impact domain of the SGRQ; X = the SGRQ total score.

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