Study objectives: To clarify the pathophysiologic
features of the relation between asthma and obesity, we measured the
effects of weight reduction on peak expiratory flow (PEF) variability
and airways obstruction, compared to simultaneous changes in lung
volumes and ventilatory mechanics in obese patients with stable
Methods: Fourteen obese asthma patients (11
women and 3 men; aged 25 to 62 years) were studied before and after a
very-low-calorie-diet period of 8 weeks. PEF variability was determined
as diurnal and day-to-day variations. FEV1 and maximal
expiratory flow values were measured with a flow-volume spirometer.
Lung volumes, airways resistance (Raw), and specific airways
conductance were measured using a constant-volume body plethysmograph.
Minute ventilation was monitored in patients in supine and standing
Results: As patients decreased their body
mass 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) to
4.5% (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 middle
part of FVC (FEF25–75) increased even when related to lung
volumes (FEF25–75/FVC; p < 0.05). Functional residual
capacity and expiratory reserve volume were significantly higher after
weight loss (p < 0.05 and p < 0.005, respectively). A significant
reduction in Raw was found (p < 0.01). Resting minute ventilation
decreased after weight loss (p = 0.01).
Weight loss reduces airways obstruction as well as PEF variability in
obese patients with asthma. The results suggest that obese patients
benefit from weight loss by improved pulmonary mechanics and a better
control of airways obstruction.