Feasibility and clinical applications of multiple breath wash-out (MBW) testing using sulphur hexafluoride in adults with bronchial asthma

Abstract

Ventilation heterogeneity is frequent in bronchial asthma and can be assessed using multiple breath wash-out testing (MBW). Most data is available in paediatric patients and using nitrogen as a tracer gas. We aimed to evaluate sulphur hexafluoride (SF 6) MBW in adult asthmatics. Spirometry, wholebody plethysmography, impulse oscillometry and SF 6-MBW were prospectively performed. MBW parameters reflecting global (lung clearance index, LCI), acinar (S acin) and conductive (S cond) ventilation heterogeneity were derived from three consecutive wash-outs. LCI was calculated for the traditional 2.5% and an earlier 5% stopping point that has the potential to reduce wash-out times. 91 asthmatics (66%) and 47 non-asthmatic controls (34%) were included in final analysis. LCI 2.5 and Lci 5 were higher in asthmatics (p < 0.001). Likewise, S acin and S cond were elevated (p < 0.001 and p < 0.01). Coefficient of variation was 3.4% for LCI 2.5 and 3.5% for LCI 5 in asthmatics. Forty-one asthmatic patients had normal spirometry. ROC analysis revealed an AUC of 0.906 for the differentiation from non-asthmatic controls exceeding diagnostic performance of individual and conventional parameters (AUC = 0.819, p < 0.05). Sf 6-MBW is feasible and reproducible in adult asthmatics. Ventilation heterogeneity is increased as compared to non-asthmatic controls persisting in asthmatic patients with normal spirometry. Diagnostic performance is not affected using an earlier LCI stopping point while reducing wash-out duration considerably. Disease control is the primary goal of asthma therapy being linked to absence of symptoms and exacerbations 1. Regrettably, up to half of the patients are poorly controlled 2,3. Despite therapeutic advances, numbers remained fairly unaltered during the last decade. The clinical and pathophysiological explanations associated with poor disease control are heterogenous. In general, more severe disease is related to more frequent exacerbations, health care contacts 3 and symptoms 4. Lung function is also impaired in severe disease indicated by a lower forced expiratory volume in one second (FEV 1) and lower forced vital capacity (FVC) 3. Both parameters represent rather central sites of obstruction. However, involvement of peripheral airways is common in the majority of asthmatic patients 5. This holds true across the whole spectrum of severity 6 and may be a consequence of several influencing factors. These include inflammation, wall thickening, smooth muscle hypertrophy, and mucus 7-10. However, changes in the lung periphery are still often missed by commonly used techniques such as spirometry. Impulse oscillometry (IOS) is an inexpensive non-invasive technique to measure airway resistance. It was shown to identify small airway obstruction 11 , the related characteristics of disease control 12,13 and response to

The validity of shortened multiple-breath washout testing using sulfur hexafluoride in the assessment of patients with COPD

“…LCI 1/20th was shown to have high intra-test repeatability and accuracy for CF discrimination from health when compared to LCI 1/40th . Similar results have been observed in asthma, where LCI 1/20th demonstrated a similar within visit coefficient of variation and diagnostic sensitivity compared to the 1/40 th test 11 .…”

Multiple breath washout (MBW) testing using sulfur hexafluoride: reference values and influence of anthropometric parameters

“…39 These findings are supported by data in patients with cystic fibrosis 40 and adults with asthma. 41 covered by either S cond or S acin . 42 Therefore, a combined interpretation of parameters representing global and local ventilation heterogeneity seems promising.…”

Diagnostic Potential of Oscillometry: A Population-based Approach

“…These results support the concept of integrating oscillometry into the clinical diagnostic routine to objectively identify early abnormalities ( 41 ). This is particularly relevant as spirometry, despite its widespread use as a single diagnostic test, may not capture certain aspects of respiratory abnormalities that specifically affect small airways ( 42 , 43 ). Another aspect to consider is that oscillometry can have a role in situations where spirometry cannot be performed or outside of major academic centers, where the quality of spirometry can be poor and where technicians, as well as patients, would prefer not to perform the test.…”