Does increased baseline ventilation heterogeneity following chest wall strapping predispose to airway hyperresponsiveness?

Abstract

Chapman DG, Berend N, Horlyck KR, King GG, Salome CM. Does increased baseline ventilation heterogeneity following chest wall strapping predispose to airway hyperresponsiveness? J Appl Physiol 113: 25-30, 2012. First published May 3, 2012 doi:10.1152/japplphysiol.01582.2011.-Baseline ventilation heterogeneity is associated with airway hyperresponsiveness (AHR) in asthma; however, it is unknown whether increased baseline ventilation heterogeneity leads to AHR or both are independent effects of similar disease pathophysiology. Reducing functional residual capacity (FRC) in healthy subjects increases baseline ventilation heterogeneity and airway responsiveness, but the relationship between the two is unclear. The aim was to determine whether an increase in baseline ventilation heterogeneity due to a reduction in FRC correlated with the increase in response to methacholine. In 13 healthy male subjects, ventilation heterogeneity was measured by multiple-breath N 2 washout before a cumulative high-dose (0.79 -200 mol) methacholine challenge. On a separate day, the protocol was performed with chest wall strapping (CWS) to reduce FRC. Indexes of ventilation heterogeneity in the convection-dependent (Scond) and diffusion-convection-dependent (Sacin) airways were calculated from the multiple-breath N 2 washout. CWS decreased FRC by 15.6 Ϯ 2.7% (P Ͻ 0.0001). CWS increased the percent fall in forced expiratory volume in 1 s during bronchial challenge (P ϭ 0.006), and the magnitude of this effect was independently determined by the effect of CWS on Sacin and FRC (r adj 2 ϭ 0.55, P ϭ 0.02). This suggests that changes in baseline ventilation heterogeneity in healthy subjects are sufficient to increase airway responsiveness, independent of the presence of disease pathology. obesity; multiple-breath nitrogen washout

The Nonallergic Asthma of Obesity. A Matter of Distal Lung Compliance

“…Interestingly, although we did find different effects of weight loss on lung volume, it was only in the nonpatients with asthma that FRC and TLC increased significantly with weight loss (Table 2). We also found no relationship between change in methacholine sensitivity and change in lung volume in our subjects (Figure 3), which is curious given that methacholine sensitivity and responsiveness have previously been shown to have a strong inverse dependence on FRC (12,23). These findings seem to contradict our hypothesis that lung compression is behind the nonallergic form of obese asthma.…”

“…Probably most at issue in this regard is the role of regional ventilation heterogeneity, such as would be modeled by two or more peripheral compartments acting in parallel, and which has been shown to accompany imposed reductions in lung volume (23). Parallel heterogeneity also increases the negative frequency dependence of resistance, but these effects occurred in our impedance data over the frequency range 5-35 Hz (Figure 2), which means that at least one of the compartments involved must have had a time-constant in the range 1/5-1/35 = 0.029-0.200 seconds.…”

“…The onset of airway hyperresponsiveness at low lung volumes has been investigated extensively in nonobese subjects (12,23,30,31), and is often explained as being caused by an impaired ability to stretch the airway wall (32). However, although obese individuals do breathe at reduced FRC, they typically have increased tidal volumes and minute ventilations compared with lean individuals (33), and so their airway smooth muscle may actually undergo more deformation during tidal breathing than control subjects.…”

Short-Term Effects of Elastic Chest Wall Restriction on Pulmonary Function in Children with Cystic Fibrosis

“…If chest wall restriction efficiently reduces hyperinflation, that is, lowering resting lung volume and modulating airflow in peripheral airways [4], airway clearance would be improved. Chest wall restriction has been shown to decrease forced vital capacity (FVC), functional residual capacity (FRC), and cardiac output and increase ventilation inhomogeneity and airway hyperresponsiveness in healthy adults [5][6][7][8][9]. These studies all used inelastic chest wall restriction, while in patients with CF the use of elastic chest wall restriction is more common.…”

Device for simulation of restrictive pathologies in healthy subjects with non-invasive mechanical ventilation

“…Due to the increase of respiratory diseases and related, as obesity [5][6][7] and thoracic injuries [8][9][10], to simulate and to understand the ventilatory response in the presence of restrictive thoracic loads is a current topic of study [11][12][13]. In order to assess the effect of restrictive thoracic loads, Chest Wall Strapping (CWS) is commonly used, which consists of applying force to the chest and abdomen with straps or girdles [11].…”