Abstract
Pulmonary function testing involves a battery of tests from the simple pulse oximetry to the cardiopulmonary exercise testing. Impulse oscillometry (IOS) is one of the newly described pulmonary function tests. It is based on the old principle of forced oscillatory technique modified and refined as per research and advances. It involves the use of sound waves during normal tidal breathing, which gives information on oscillatory pressure-flow relationships and eventually resistance and reactance. The resistance at 20 Hz (R20) represents the resistance of the large airways. The resistance at 5 Hz (R5) means the total airway resistance. (R5-R20) reflects resistance in the small airways. The reactance at 5 Hz (X5) indicates the elastic recoil of the peripheral airways. Resonant frequency and area of reactance are also measured. IOS has major uses in diagnosis and control of asthma in children and the elderly, where spirometry is otherwise normal. IOS has been studied in other respiratory diseases like COPD, ILD and supraglottic stenosis.
Highlights
Conventional spirometry has been in use since many decades
Impulse oscillometry is defined as a variant of forced oscillation technique (FOT) described by Dubois over 50 years ago, which permits passive measurement of lung mechanics
The principle of impulse oscillometry (IOS) is based on superimposition of sound waves on normal tidal breathing, which leads to disturbances in flow and pressure across the airways, leading to an ultimate output of respiratory resistance, reactance and impedance using the fast fourier transform (FFT) technique
Summary
Conventional spirometry has been in use since many decades. In 1956, Dubois et al described the forced oscillation technique (FOT) to measure lung functions using single frequency sound waves, which was easy to perform and provided more insight into the lung mechanics as compared to the simple spirometry [1]. In 1975, Michaelson et al improvised the technique to use multiple frequency sound waves which was named impulse oscillometry (IOS) [2]. It was not until 1998 when Jaeger could make computerised IOS commercially available [3,4,5]
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