Influence of ventilation inhomogeneity on diffusing capacity of carbon monoxide in smokers without COPD

Single and multiple breath nitrogen washout compared with the methacholine test in patients with suspected asthma and normal spirometry

BACKGROUND

Methods used to assess ventilation heterogeneity through inert gas washout have been standardised and showed high sensitivity in diagnosing many respiratory diseases. We hypothesised that nitrogen single or multiple breath washout tests, respectively nitrogen single breath washout (N2SBW) and nitrogen multiple breath washout (N2MBW), may be pathological in patients with clinical suspicion of asthma but normal spirometry. Our aim was to assess whether N2SBW and N2MBW are associated with methacholine challenge test (MCT) results in this population. We also postulated that an alteration in SIII at N2SBW could be detected before the 20% fall of forced expiratory volume in the first second (FEV1) in MCT.

STUDY DESIGN AND METHODS

This prospective, observational, single-centre study included patients with suspicion of asthma with normal spirometry. Patients completed questionnaires on symptoms and health-related quality-of-life and underwent the following lung function tests: N2SBW (SIII), N2MBW (Lung clearance index (LCI), Scond, Sacin), MCT (FEV1 and sGeff) as well as N2SBW between each methacholine dose.

RESULTS

182 patients were screened and 106 were included in the study, with mean age of 41.8±14 years. The majority were never-smokers (58%) and women (61%). MCT was abnormal in 48% of participants, N2SBW was pathological in 10.6% at baseline and N2MBW abnormality ranged widely (LCI 81%, Scond 18%, Sacin 43%). The dose response rate of the MCT showed weak to moderate correlation with the subsequent N2SBW measurements during the provocation phases (ρ 0.34-0.50) but no correlation with N2MBW.

CONCLUSIONS

Both MCT and N2 washout tests are frequently pathological in patients with suspicion of asthma with normal spirometry. The weak association and lack of concordance across the tests highlight that they reflect different but not interchangeable pathological pathways of the disease.

The Role of Pulmonary Function Testing in the Diagnosis and Management of COPD

Pulmonary function testing (PFT) has a long and rich history in the definition, diagnosis, and management of COPD. For decades, spirometry has been regarded as the standard for diagnosing COPD; however, numerous studies have shown that COPD symptoms, pathology, and associated poor outcomes can occur, despite normal spirometry. Diffusing capacity and imaging studies have called into question the need for spirometry to put the "O" (obstruction) in COPD. The role of exercise testing and the ability of PFTs to phenotype COPD are reviewed. Although PFTs play an important role in diagnosis, treatment decisions are primarily determined by symptom intensity and exacerbation history. Although a seminal study positioned FEV1 as the primary predictor of survival, numerous studies have shown that tests other than spirometry are superior predictors of mortality. In years past, using spirometry to screen for COPD was promulgated; however, this only seems appropriate for individuals who are symptomatic and at risk for developing COPD.

School-age structural and functional MRI and lung function in children following lung resection for congenital lung malformation in infancy

BACKGROUND

The management of asymptomatic congenital lung malformations is debated. Particularly, there is a lack of information regarding long-term growth and development of the remaining lung in children following lung resection for congenital lung malformations. In addition to conventional pulmonary function tests, we used novel functional magnetic resonance imaging (MRI) methods to measure perfusion and ventilation.

OBJECTIVE

To assess functionality of the remaining lung expanded into the thoracic cavity after resection of congenital lung malformations.

MATERIALS AND METHODS

A prospective, cross-sectional pilot study in five children who had surgery for congenital lung malformations during infancy. Participants had structural and functional MRI as well as spirometry, body plethysmography and multiple breath washout at school age.

RESULTS

Structural MRI showed an expansion of the remaining lung in all cases. Fractional ventilation and relative perfusion of the expanded lung were locally decreased in functional MRI. In all other parts of the lungs, fractional ventilation and relative perfusion were normal in all children. There was an association between overall impairment of perfusion and elevated lung clearance index. The results of spirometry and body plethysmography varied between patients, including normal lung function, restriction and obstruction.

CONCLUSION

Fractional ventilation and relative perfusion maps from functional MRI specifically locate impairment of the remaining lung after lung resection. These changes are not captured by conventional measures such as structural MRI and standard pulmonary function tests. Therefore, following lung resection for congenital lung malformation, children should be investigated more systematically with functional lung MRI.