• Kazutaka Mori, Toshihiro Shirai, Masashi Mikamo, Yuichiro Shishido, Takefumi Akita, Satoru Morita, Kazuhiro Asada, Masato Fujii, Takafumi Suda, and Kingo Chida.
• Department of Respiratory Medicine, Shizuoka General Hospital, 4-27-1 Kita-ando, Aoi, Shizuoka, Japan.
• COPD. 2011 Dec 1; 8 (6): 456-63.

BackgroundThe forced oscillation technique (FOT) is a noninvasive method with which to measure respiratory system resistance (Rrs) and reactance (Xrs) at a wide range of frequencies during breathing at rest in a short time. The purpose of this study was to assess the differences in Rrs and Xrs between patients with chronic obstructive pulmonary disease (COPD) and asthma using a new method of FOT with colored 3-dimensional visualization.MethodsFifty-one patients with stable COPD and 49 patients with controlled or partly controlled asthma were enrolled. Whole-breath or within-breath changes of Rrs and Xrs were measured and compared between the diseases.ResultsThe colored 3-dimensional images clarified the complex oscillatory properties of the respiratory system. Whole-breath resistance (the difference in Rrs at 5 and 20 Hz) and reactance (Xrs at 5 Hz and resonant frequency), and within-breath changes in reactance (Xrs at 5 Hz and resonant frequency) discriminated between patients with COPD and asthma. In multivariate regression analyses, inspiratory-expiratory differences in Xrs at 5 Hz contributed significantly to the differentiation between COPD and asthma, independent of age, gender, body weight, and pulmonary function.ConclusionThis new method of FOT is useful in the differential diagnosis of COPD and asthma.

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