Frequency dependence of compliance in the evaluation of patients with unexplained respiratory symptoms

Abstract

Frequency dependence of compliance (FDC) reflects non-homogeneous ventilatory distribution and, in the presence of a normal measured airway resistance, suggests peripheral airways dysfunction. This study evaluated peripheral airway function and bronchial reactivity in irritant exposed or non-exposed individuals with normal routine pulmonary function tests (PFTs) who had persistent unexplained lower respiratory symptoms. Twenty-two patients were identified with persistent respiratory symptoms and with normal chest X-ray and PFTs. Twenty were non-smokers; two had stopped smoking more than 10 years before evaluation. Twelve patients had been exposed to irritants in their workplaces or at home. Non-specific bronchial hyper-reactivity (nsBHR) and FDC, pre- and post-bronchodilator, were measured in all patients. Studies were repeated in 6/12 irritant-exposed subjects after exposure removal and inhaled corticosteroid treatment. Whereas 12/22 patients had nsBHR, all 22 subjects demonstrated FDC [dynamic lung compliance/static lung compliance Cdyn,1 / Cst,1 at respiratory frequency 60 min(-1) (f60), mean 46%, range 27-67%]. After bronchodilator administration, a 15% improvement Cdyn,1 was observed most consistently at f60 (mean% improvement 26%, 95% CI 14-38%) and in subjects without nsBHR. However, Cdyn,1 at f60 did not return to normal after inhaled bronchodilator. Irritant-exposed and unexposed individuals appeared similar in results of testing for FDC and nsBHR. FDC and its response to bronchodilators provide objective physiological measures of an airway abnormality which may provide a basis for clinical symptoms in patients with normal routine pulmonary function studies. The presence of persistently abnormal FDC after bronchodilator (BD) and on follow up studies may reflect chronic inflammatory and/or structural changes in the airways in addition to bronchoconstriction.

Lessons From the World Trade Center Disaster

“…[6][7][8][9][10] Studies postulated primary airway rather than parenchymal disease based on normal chest radiographs and either bronchial hyperreactivity and/or airway wall thickening and AT on CT scan examination. 7,10,12,13,29 The fall in VC in fi refi ghters from before to after September 11, 2001, correlated with degree of AT assessed by plethysmography, 12 and reduced VC and TLC was associated with AT on CT scan in other fi rst responders. 11 The present study extends these observations by demonstrating normal static lung mechanics, normal maximal Pel, and absence of parenchymal disease on high-resolution CT scan.…”

“…Data were obtained (n 5 16) using an esophageal catheter (AKRAD Laboratories; CooperSurgical Inc ) positioned in the distal esophagus. 29,30 Static lung compliance (Cst,1) was measured after two IC maneuvers by periodically occluding the airway during a passive exhalation from TLC to FRC. Specifi c lung compliance (Csp) was calculated by dividing Cst,1 by FRC.…”

Occupational Asthma and Lower Airway Disease Among World Trade Center Workers and Volunteers

“…Besides the studies mentioned, several findings have suggested the presence of small airway dysfunction more frequently than diagnosed in symptomatic patients. Those findings have included the following: 1) the frequent finding of reduced FVC in spirometry (with preserved TLC) [30]; 2) the low frequency of methacholine reactivity generally and in individuals with asthma-like clinical presentations [34]; 3) FVC reduction response to bronchoprovocation testing [35]; 4) air trapping by paired inspiratory/expiratory chest CT scans [33]; and 5) evidence of long-term, accelerated FVC decline in those lacking bronchodilator response, which could suggest the effect of inflammatory remodeling occurring at the level of the small airways [36•, 37]. A study using impulse oscillometry technique lacked a characterization of occupational lung disease diagnoses [38], and when that is done, this technique does not seem to provide sufficiently specific diagnostic or physiologic information [39].…”

Distal Airway Function Assessed by Oscillometry at Varying Respiratory Rate: Comparison with Dynamic Compliance

“…Oscillations of airflow may be induced either by volitional changes in respiratory rate or by externally applied pressure oscillations. Frequency dependence of compliance (FDC) is an established marker of distal airway dysfunction; however, its clinical application is limited by the need for esophageal manometry (9)(10)(11). Impulse oscillometry is a non-invasive technique to assess distal airway function involving externally applied pressure oscillations.…”