![]() Since the oscillatory mechanics have different physiological features between the inspiratory and expiratory phases, especially in patients with obstructive diseases, such an approach may provide a new insight into the underlying pathophysiology of obstructive diseases. In a commercially available IO (Master Screen-IOS CareFusion, Germany), the interval of the impulse occurrence is 0.2 s, which enables evaluation of the within-breath behaviour of the oscillatory mechanics with high temporal resolution. The temporal resolution of IO is determined mainly by the duration of the oscillatory pressure and flow in signal processing, which is closely related to the interval of the impulse occurrence or minimal oscillatory frequency in the evaluation. 9 Other studies also have focused on the different oscillatory properties between the respiratory phases of patients with COPD and those with bronchial asthma. Recently, Paredi et al reported that inspiratory–expiratory Xrs analysis (5 Hz) using IO differentiated patients with bronchial asthma from those with COPD. 8 Rrs is higher, and Xrs is more negative during expiration than inspiration in most patients with COPD. 6 In patients with COPD, owing to the airway narrowing during tidal expiration, 7 the oscillatory properties are also characterised by significantly different Rrs and Xrs in the inspiratory and expiratory phases. In patients with obstructive diseases, the oscillatory flow resistance of the respiratory system tends to be increased with the degree of the airway obstruction, resulting in an increase in Rrs and negative values in Xrs. 5 However, whether it could be expected to play an important role to screen, diagnose, staging, and control obstructive diseases such as chronic obstructive pulmonary disease (COPD) and bronchial asthma is controversial and currently under discussion. 4 A number of studies have demonstrated that the IO is able to identify airway obstruction. IO enables one to measure the respiratory system impedance (Zrs), which consists of the real part as resistance (Rrs) and the imaginary part as reactance (Xrs) over a wide range of the oscillatory frequency. 1–3 Currently, the FOT using impulses, impulse oscillometry (IO), is increasingly used in clinical research. The forced oscillation technique (FOT) is a simple method for assessing the oscillatory flow resistance of the respiratory system, and has provided important findings in respiratory physiology.
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