Bronchodilator Response in Patients with COPD, Asthma-COPD-Overlap (ACO) and Asthma, Evaluated by Plethysmographic and Spirometric z-Score Target Parameters

Abstract

Background Airflow reversibility criteria in COPD are still debated – especially in situations of co-existing COPD and asthma. Bronchodilator response (BDR) is usually assessed by spirometric parameters. Changes assessed by plethysmographic parameters such as the effective, specific airway conductance (sG eff ), and changes in end-expiratory resting level at functional residual capacity (FRC pleth ) are rarely appreciated. We aimed to assess BDR by spirometric and concomitantly measured plethysmographic parameters. Moreover, BDR on the specific aerodynamic work of breathing (sWOB) was evaluated. Methods From databases of 3 pulmonary centers, BDR to 200 g salbutamol was retrospectively evaluated by spirometric (∆FEV 1 and ∆FEF 25–75 ), and plethysmographic (∆sG eff , ∆FRC pleth , and ∆sWOB) parameters in a total of 843 patients diagnosed as COPD (478 = 57%), asthma-COPD-overlap (ACO) (139 = 17%), or asthma (226 = 27%), encountering 1686 BDR-measurement-sets (COPD n = 958; ACO n = 276; asthma n = 452). Results Evaluating z-score improvement taking into consideration the whole pre-test z-score range, highest BDR was achieved by combining ∆sG eff and ∆FRC detecting BDR in 62.2% (asthma: 71.4%; ACO: 56.7%; COPD: 59.8%), by ∆sG eff in 53.4% (asthma: 69.1%; ACO: 51.6%; COPD: 47.4%), whereas ∆FEV 1 only distinguished in 10.6% (asthma: 21.8%; ACO: 18.6%; COPD: 4.2%). Remarkably, ∆sWOB detected BDR in 49.4% (asthma: 76.2%; ACO: 47.8%; COPD: 46.9%). Conclusion BDR largely depends on the pre-test functional severity and, therefore, should be evaluated in relation to the pre-test conditions expressed as ∆z-scores, considering changes in airway dynamics, changes in static lung volumes and changes in small airway function. Plethysmographic parameters demonstrated BDR at a significant higher rate than spirometric parameters.

Functional Predictors Discriminating Asthma–COPD Overlap (ACO) from Chronic Obstructive Pulmonary Disease (COPD)

“…We have recently demonstrated that the discriminating power of BDR distinguishing asthma from ACO and COPD is significantly better achieved by sG eff than FEV 1 . 16 Moreover, sWOB also improved in asthma by 76.2%, in ACO by 47.8%, and in COPD by 46.9%, compared to FEV 1 (asthma: 21.8%; ACO: 18.6%; COPD: 4.2%). 16 BDR assessed by several advanced lung function parameters was recently also studied by Jarenbäck et al, 99 suggesting that in addition to flow-response, volume-response should also be evaluated.…”

“… 16 Moreover, sWOB also improved in asthma by 76.2%, in ACO by 47.8%, and in COPD by 46.9%, compared to FEV 1 (asthma: 21.8%; ACO: 18.6%; COPD: 4.2%). 16 BDR assessed by several advanced lung function parameters was recently also studied by Jarenbäck et al, 99 suggesting that in addition to flow-response, volume-response should also be evaluated. The overall clinical aim in COPD is to improve function in the small peripheral airways by improving flow (flow responders), as well as decreasing air trapping and pulmonary hyperinflation (volume responders).…”

“…The sR eff and sR tot have been well established as functional characteristics approximating the shape of such sRaw-loops. 16 , 32 , 33 , 41 , 106 , 124 Noteworthy, is that, in contrast to the previously used sR aw reflecting proximal airway abnormalities, sR eff and the reciprocal value sG eff were proven to be a target parameter reflecting small airways function. 16 , 97 , 98 , 125 Moreover, Mahut et al suggested that sR tot and sR eff can be considered equivalent and correlated with indices that explore peripheral airways (RV/TLC), and that these two parameters are statistically linked to activity-related dyspnea in COPD patients.…”

“… 16 , 32 , 33 , 41 , 106 , 124 Noteworthy, is that, in contrast to the previously used sR aw reflecting proximal airway abnormalities, sR eff and the reciprocal value sG eff were proven to be a target parameter reflecting small airways function. 16 , 97 , 98 , 125 Moreover, Mahut et al suggested that sR tot and sR eff can be considered equivalent and correlated with indices that explore peripheral airways (RV/TLC), and that these two parameters are statistically linked to activity-related dyspnea in COPD patients. 106 The open shape of the sRaw-loop is associated with changes in the elastic recoil pressure and collapse during quiet tidal breathing due to the changes in airway resistance exhibited between inspiratory and expiratory flow.…”

“… 16 By that the degree of functional severity of airflow limitation (FEV 1 , FEV 1 /FVC), small airways dysfunction (FEF 25-75 ), dynamic airway dysfunction (sR eff , sR tot , sWOB), pulmonary hyperinflation (FRC pleth ), trapped gases (V TG FRC ) and gas diffusion disturbance (DL CO , K CO ) could be assessed within the 3 diagnostic classes, with the advantage that all parameters could functionally be comparable since they have been expressed as z-scores and, hence, gender-, age-, height- and ethnicity-corrected, as previously recommended. 16 , 35–38…”