The subjects were advised to breathe quietly from a mouth piece while wearing a nose-clip during the measurements. The IO measurement was performed in the sitting position. Quartile time fractions numbered 1–4 were set and added to the label as respiratory phase 1 to 4 and phase 5 to 8, respectively ( figure 1). After the comma-separated value data files were opened on our personal computers, every impulse data point was labelled as inspiratory or expiratory phase based on the spontaneous airflow direction.
#IOS LABMANAGER CAREFUSION SERIAL#
The comma-separated value data files showing the serial values of each component by every 0.2 s were extracted after the measurements. The R5 (Rrs at 5 Hz), R20 (Rrs at 20 Hz), X5 (Xrs at 5 Hz) and Fres (resonant frequency of Xrs) were provided as real-time data.
#IOS LABMANAGER CAREFUSION SOFTWARE#
The respiratory system impedance (Zrs), ratio of the mouth pressure to airflow according to the impulses, the Rrs, its real component, and the Xrs, its imaginary component, were automatically calculated using the attached software including fast Fourier transform analysis (LAB manager, CareFusion version 4.65). The impulse pressure was produced with alternate changes in two directions (positive and negative). Continuous impulses (pyramidal-form pulses, 5 pulses/s), which contained sinusoidal waves of a broad-frequency spectrum, were applied as the forced oscillation. The oscillatory mechanics were assessed using a commercially available IO device (Master Screen-IOS CareFusion, Germany). This approach may reveal technical advances in IO and establish an approach for evaluating the physiological features in respiration in patients with COPD. Using this approach, we studied the relationship between the within-breath behaviour and the COPD severity. Based on our methods that were originally developed using raw Rrs and Xrs data retrieved from a commercially available IO device, eight moments during the respiratory cycle were produced and studied to elucidate the within-breath behaviour. In the present study, we report a new approach using IO for assessing the within-breath behaviour of the oscillatory mechanics during tidal breathing. 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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