The inspired sinewave test (IST) serves as a superior independent predictor of symptom severity compared with spirometry in chronic obstructive pulmonary disease (COPD), according to a study published in the International Journal of Chronic Obstructive Pulmonary Disease.

There is marked variability in the symptoms and outcomes of patients with COPD, which are poorly predicted by spirometry/ forced expiratory volume in one second percent predicted (FEV1%pred). Furthermore, as spirometry requires the performance of potentially distressing respiratory maneuvers, which are to some extent user-effort dependent, there is need for non-invasive and simple-to-perform techniques to identify subtypes of COPD [that] are more closely related to clinically relevant outcomes,” the researchers wrote.

The IST works by sinusoidally regulating concentrations of a tracer gas (N2O) over consecutive tidal breaths. According to the researchers, a single-compartment tidal-ventilation lung model processes the amplitude/phase of the expired N2O sinewave and estimates cardiopulmonary variables, including effective lung volume and indices of ventilatory heterogeneity.

In this study, 83 patients with COPD and 53 healthy controls performed the IST test, standard pulmonary function tests, and completed symptom severity questionnaires.

According to the results, the researchers wrote, “IST indices of ventilatory heterogeneity were superior and independent predictors of symptom severity vs FEV1%pred and has potential as a non-invasive and simple-to-perform method to stratify patients into subgroups related to clinically relevant features of COPD.”

Keywords: COPD, lung function test, medical device, nitrous oxide, ventilatory heterogeneity