Impulse oscillometry (IOS) is a noninvasive lung function test that measures airway resistance and reactance by sending small pressure oscillations through the airways while the patient breathes normally. It detects large- and small-airway dysfunction (parameters like R5, R20, X5), is quick and easy for children or frail patients, and requires no forced breaths, so it’s useful when spirometry isn’t feasible.

Impulse oscillometry (IOS) reports key values: R5 (total airway resistance), R20 (central resistance), and R5–R20 (peripheral/small‑airway resistance). X5 (reactance) becomes more negative with obstruction; AX (area of reactance) and Fres (resonant frequency) increase in small‑airway disease. Compare measured vs predicted and assess bronchodilator response—improvement in R5 or X5 suggests reversible obstruction. Clinical correlation with symptoms and spirometry is essential.

Spirometry measures airflow and lung volumes during forced breathing maneuvers (FEV1, FVC); it’s effort‑dependent and detects global obstructive or restrictive patterns. Impulse oscillometry assesses respiratory resistance and reactance during quiet tidal breathing using pressure oscillations; it’s effort‑independent, easier for children or frail patients, and more sensitive to small‑airway dysfunction.

Impulse oscillometry values vary with age and height. Typical adult reference ranges: R5 (total resistance) ≈ 0.2–0.5 kPa·s/L, R20 (proximal resistance) ≈ 0.1–0.3 kPa·s/L, X5 (reactance at 5 Hz) ≈ −0.05 to −0.30 kPa·s/L, resonant frequency (Fres) <12–15 Hz, and AX (area of reactance) generally <0.3–1.0 kPa·L−1. Interpret with clinical reference equations.

Oscillometry (forced oscillation technique) applies small external pressure oscillations to the airway during normal breathing and measures resulting flow and pressure to calculate respiratory impedance. Frequency-dependent resistance reflects airway caliber; reactance reflects elastic and inertial properties of the lung and peripheral airways. It's noninvasive, requires minimal patient cooperation, and sensitively detects central and small-airway dysfunction and changes in lung mechanics.

Oscillometry (forced oscillation technique) is used to diagnose and monitor respiratory conditions by measuring airway resistance and reactance during normal breathing. It’s especially useful for detecting obstructive airway diseases such as asthma and COPD, assessing small‑airways involvement, and testing children or patients who cannot perform conventional spirometry. It also helps track treatment response and disease progression.