Observations on the physiological interactions between obesity and asthma

Case Western Reserve University, Cleveland, Ohio, United States
Journal of Applied Physiology (Impact Factor: 3.43). 10/2008; 105(5):1533-41. DOI: 10.1152/japplphysiol.01260.2007
Source: PubMed

ABSTRACT To explore whether asthma and obesity share overlapping pathogenic features, we examined the impact of each alone, and in combination, on multiple aspects of lung function. We reasoned that if they influenced the lungs through similar mechanisms, the individual physiological manifestations in the comorbid state should interact in a complex fashion. If not, then the abnormalities should simply add. We measured specific conductance, spirometry, lung volumes, and airway responsiveness to adrenergic and cholinergic agonists in 52 normal, 53 asthmatic, 52 obese, and 53 asthmatic and obese patients using standard techniques. Six-minute walks were performed in subsets from each group. Asthma significantly lowered specific conductance and the spirometric variables while increasing airway reactivity and residual volume. Obesity also reduced the spirometric variables as well as total lung capacity and functional residual capacity. Residual volume, specific conductance, and airway responsivity were unaltered. With comorbidity, the disease-specific derangements added algebraically. Features that existed in isolation appeared unchanged in the combination, whereas shared ones either added or subtracted depending on the individual directional changes. Synergistic interactions were not observed. Body mass index weakly correlated with spirometry and lung volumes in asthma, but not with specific conductance or bronchial reactivity. Exercise performance did not aid in differentiation. Our findings indicate asthma and obesity appear to influence the respiratory system through different processes.

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    • "The reduced EELV in obesity also means that the airways resistance is proportionately increased [40], in absolute terms [41], reflecting the reduced airway diameter compared with normal weight individuals. It is noteworthy that when the volume differences in health and obesity are accounted for as with measurements of specific airway resistance or specific conductance, this difference in airway resistance disappears [40] [42] [43]. In obesity, closing volume may occur at volumes above the lower EELV [37, 44–46]; thus, significant airway closure and gas trapping may occur in basal lung segments during the quiet tidal breathing cycle. "
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