Mechanical effects of obesity on airway responsiveness in otherwise healthy humans

Abstract

We investigated whether obesity is associated with airway hyperresponsiveness in otherwise healthy humans and, if so, whether this correlates with a restrictive lung function pattern or a decreased number of sighs at rest and/or during walking. Lung function was studied before and after inhaling methacholine (MCh) in 41 healthy subjects with body mass index ranging from 20 to 56. Breathing pattern was assessed during a 60-min rest period and a 30-min walk. The dose of MCh that produced a 50% decrease in the maximum expiratory flow measured in a body plethysmograph (PD50MCh) was inversely correlated with body mass index (r2=0.32, P<0.001) and waist circumference (r2=0.25, P<0.001). Significant correlations with body mass index were also found with the maximum changes in respiratory resistance (r2=0.19, P<0.001) and reactance (r2=0.40, P<0.001) measured at 5 Hz. PD50MCh was also positively correlated with functional residual capacity (r2=0.56, P<0.001) and total lung capacity (r2=0.59, P<0.001) in men, but not in women. Neither PD50MCh nor body mass index correlated with number of sighs, average tidal volume, ventilation, or breathing frequency. In this study, airway hyperresponsiveness was significantly associated with obesity in otherwise healthy subjects. In obese men, but not in women, airway hyperresponsiveness was associated with the decreases in lung volumes.

Effect of Obesity on Asthma Phenotype is Dependent upon Asthma Severity

“…Obesity may also reduce airway caliber 30 , allowing a greater increase in resistance for a given absolute reduction in airway diameter and manifesting as increased airway reactivity. Data from healthy subjects suggested that airway reactivity is inversely correlated with BMI 33 . Others have suggested that asthma severity in obesity is affected by altered levels of adipokines and inflammatory cytokines 34,35 .…”

“…One might hypothesize that very mild asthmatics would behave like non-asthmatic subjects. However, data concerning the relationship between obesity and airway hyperreactivity in otherwise healthy subjects are conflicting, with some studies supporting an association 33,40,44–47 and others not 7,39,41,48 .…”

Airway Responsiveness Measured by Forced Oscillation Technique in Severely Obese Patients, before and after Bariatric Surgery

“…The prevalence of both obesity and asthma has increased worldwide in recent years, and obesity has been implicated as a risk factor for asthma and as a predisposing factor for airway hyperresponsiveness (AHR) (1)(2)(3).…”

Airway‐Parenchymal Interdependence

“…The shear modulus of the lung has been estimated by indenting the pleural surface of the lung inflated to variety of transpulmonary pressures and measuring the surface indentation as a function of the applied force (28, 45). The dimensions of the bulk and shear moduli are the same as for pressure (force per unit area) and the results show a value for the shear modulus of ~0.7Ptp, while the bulk modulus ranges from 3Ptp to 7Ptp as the lung volume changes from 20% to 80% of the total lung capacity (43, 77). This means that it is much easier to distort lung’s shape than to inflate the lung.…”

“…As mentioned above, breathing at low lung volume increases airway responsiveness in normal individuals (20) and could contribute to the airway hyperresponsiveness in obese individuals. Torchio et al found linear relationships between body mass index and measures of airway sensitivity (PD50) and maximal response to inhaled methacholine; more obese individuals required a lower dose to produce the airway narrowing and their maximal achievable airway narrowing was greater (77). This issue, however, is still unsettled, as evidenced by a recent study from Salome et al, who found no difference in airway sensitivity or maximal response in a direct comparison of obese and non-obese normal subjects (69).…”