[A simple method to assess dynamic hyperinflation outside a pulmonary function test laboratory: The metronome-paced tachypnea test].

Abstract

Lung dynamic hyperinflation (DH) is one of the main determinants of dyspnea in chronic respiratory disease patients. Producing evidence of DH is critical during dyspnea assessment, the objectives being to explain the cause, to target treatments, and to monitor their efficacy. The gold standard method consists in repeated measurement of inspiratory capacity (IC) during cardiopulmonary exercise testing (CPET). Unfortunately, access to CPET is limited and assessment of IC during CPET can be challenging in some patients. An alternative method consists in assessment of IC during the testing known as metronome-paced tachypnea (MPT) challenge. This method is feasible, repeatable, valid (i.e. corelated with dyspnea patients' activities of daily living), and responsive to treatments. However, while its diagnostic performance is acceptable, it is lacking in specificity. Methodological standardization is detailed in the present review, as are the differences between IC changes in CPET and in MPT. As a means of assessing DH, MPT challenge is not only applicable to patients outside a pulmonary function test laboratory, but also easily affordable to any chest physician equipped with a simple spirometry device. A diagnosis threshold of 11% for IC decrease during MPT challenge can be used, albeit while bearing in mind the possibility of a false positive result. Moreover, assessment of IC variations during MPT can help to monitor a patient's overall evolution and response to treatments.