Contribution of respiratory resistance variability measured by forced oscillation technique (FOT) to assess the likelihood of asthma diagnosis

Background: diagnosis of asthma is based on respiratory symptoms and airflow obstruction, both characterized by variability over time, assessed by questionnaires and expiratory peak flow (PEF) monitoring (GINA report 2015). Pathophysiology of asthma is characterized by airway hyperresponsiveness, which may be assessed by metacholine (MCh) challenge and more recently by measuring variability of inspiratory resistance at 5 Hz (R insp5 ) by FOT (Gulotta et al. AJRCCM 2012;185: 1330-1331). Aim: to investigate the variability of R insp5 measured by FOT compared to PEF variability in assessing patients reporting asthma symptoms. Methods: 21 healthy, 28 mild asthmatics and 16 subjects with asthma symptoms but negative MCh challenge test (MChNeg) were monitored for 14 consecutive days by FOT and PEF measured twice a day (morning and evening). Results: R insp5 variability, expressed as standard deviation (SD 14Rinsp ) and PEF variability were equally significantly higher in asthmatics compared to MChNeg subjects, while only R insp5 variability was significantly higher in MChNeg vs healthy subjects. Conclusions: day-to-day inspiratory resistance variability on a temporal window of 14 days measured by FOT could be employed at home in remote mode in order to assess subjects with asthma like symptoms but negative MCh challenge. The clinical and pathophysiological characteristics of these subjects need to be furtherly investigated.