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Effects of Weight Loss on Peak Flow Variability, Airways Obstruction, and Lung Volumes in Obese Patients With Asthma

      Study objectives

      To clarify the pathophysiologicfeatures of the relation between asthma and obesity, we measured theeffects of weight reduction on peak expiratory flow (PEF) variabilityand airways obstruction, compared to simultaneous changes in lungvolumes and ventilatory mechanics in obese patients with stableasthma.

      Methods

      Fourteen obese asthma patients (11women and 3 men; aged 25 to 62 years) were studied before and after avery-low-calorie-diet period of 8 weeks. PEF variability was determinedas diurnal and day-to-day variations. FEV1 and maximalexpiratory flow values were measured with a flow-volume spirometer.Lung volumes, airways resistance (Raw), and specific airwaysconductance were measured using a constant-volume body plethysmograph.Minute ventilation was monitored in patients in supine and standingpositions.

      Results

      As patients decreased their bodymass index (SD) from 37.2 (3.7) to 32.1(4.2) kg/m2(p < 0.001), diurnal PEF variation declined from 5.5% (2.4) to4.5% (1.5) (p = 0.01), and day-to-day variation declined from 5.3%(2.6) to 3.1% (1.3) (p < 0.005). The mean morning PEF,FEV1, and FVC increased after weight loss (p = 0.001,p < 0.005, and p < 0.05, respectively). Flow rate at the middlepart of FVC (FEF25–75) increased even when related to lungvolumes (FEF25–75/FVC; p < 0.05). Functional residualcapacity and expiratory reserve volume were significantly higher afterweight loss (p < 0.05 and p < 0.005, respectively). A significantreduction in Raw was found (p < 0.01). Resting minute ventilationdecreased after weight loss (p = 0.01).

      Conclusion

      Weight loss reduces airways obstruction as well as PEF variability inobese patients with asthma. The results suggest that obese patientsbenefit from weight loss by improved pulmonary mechanics and a bettercontrol of airways obstruction.

      Key words

      Abbreviations:

      AFV (area under the expiratory flow volume curve), BHR (bronchialhyperresponsiveness), BMI (body mass index), Dlco (diffusing capacity of the lung for carbonmonoxide), ERV (expiratory reserve volume), FEF25– 75 (flow rate at the middle part of FVC), FRC (functional residual capacity), NS (not statisticallysignificant), PD15 (provocative dose causing a 15% fallin FEV1), PEF (peak expiratory flow), Raw (airwaysresistance), RR (respiratory rate), RV (residual volume), SGaw (airways conductance), TLC (total lung capacity), TLC-B (TLC measured using body plethysmograph), TLC-He (TLCmeasured using the single-breath helium dilution method), VAS (visualanalogue scale), Ve (minute ventilation), VLCD (very-low-calorie-diet), Vt (tidal volume)
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