Advanced Oscillometry Insights: Managing Asthma and COPD

Oscillometry is a non-invasive method for measuring the mechanical properties of the respiratory system, which can enhance our understanding and management of lung diseases such as asthma and COPD.

This technique offers special advantages in situations where spirometry and other lung function tests are not suitable for patients, such as infants, people with neuromuscular diseases, those who have difficulty following instructions (such as children or those with neurological problems), those with sleep apnea, and those in need of critical care.

In this article, we focus on the clinical applications of oscillometry for the diagnosis, treatment, and monitoring of asthma and COPD.

The respiratory system impedance (Zrs) is plotted against frequency. Zrs consists of a real component represented by resistance (Rrs) and an imaginary component expressed as reactance (Xrs). Rrs and Xrs at specific frequencies are denoted by the frequency at which they are measured (for example, Rrs5 = Rrs at 5 Hz, Rrs20 = Rrs at 20 Hz). The frequency at which Xrs crosses zero is the resonance frequency (fres). Below fres, Xrs is dominated by elastance, and above fres, Xrs is dominated by inertia.

The area under the Xrs and Zrs = 0 curve is an integrated measure of low-frequency Xrs; it starts from the lowest frequency up to fres, known as the area under the Xrs curve, AX. The lowest frequency of AX is shown at 5 Hz, but it can be estimated starting from any frequency. It should be noted that the Zrs spectrum shown in the image above is characteristic of a healthy adult. In healthy young children, Rrs values and frequency dependence would be relatively higher, Xrs would be more negative, and fres would notably shift to the right (resulting in an increase in AX).

On the other hand, various studies have shown that a bronchodilator response (BDR) based on oscillometric parameters is better than one based on forced expiratory volume in 1 second (FEV1) for distinguishing asthmatic children from healthy children.

Some recent studies have shown that oscillometry and other parameters related to peripheral airway function can correlate with symptom improvement in patients with poorly controlled asthma receiving inhaled corticosteroids and long-acting β2 agonists (ICS/LABA).

Oscillometric indices are also sensitive to improvements in asthma in response to mepolizumab therapy. Therefore, these findings suggest that oscillometry plays an important and complementary role to spirometry in identifying and monitoring treatment response in asthmatic patients.

Oscillometry can also be a valuable test for early detection of smoking-related adverse effects before COPD diagnosis. Several studies have found that many smokers with normal spirometry show abnormalities in Zrs; in fact, up to 60% of them exhibited some anomaly in oscillometry results.

Oscillometry can also aid in categorizing the severity of COPD. Patients with this disease have significantly higher values of Rrs and more negative values of Xrs than healthy individuals, with these changes proportional to the degree of airway obstruction. In fact, intrabreath oscillometry examination has been used to demonstrate evidence of tidal expiratory flow limitation (EFLT) in COPD.

In these patients, reactance and resistance are higher during expiration compared to inspiration, reflecting dynamic airway compression and expiratory flow limitation. The underlying mechanisms of airway collapse during tidal breathing are uncertain, although empirically defined thresholds based on the difference between inspiratory and expiratory Xrs have been shown to be a sensitive and specific method for detecting EFLT.

The inspiratory-expiratory difference in Xrs and its variability over time are also associated with increased dyspnea. Additionally, this index is linked to accelerated impairment of exercise capacity and a higher likelihood of exacerbations, independently of the degree of impairment shown by spirometry.

In COPD patients, oscillometry has also revealed greater variations in lung function over time, as well as greater bronchodilator responses than expected by spirometry alone. This reinforces that the disease's pathogenesis extends beyond fixed airway obstruction and reversibility in large airways.

SCHILLER-GANSHORN contribute to efforts to offer accurate and early diagnoses, providing equipment with advanced technology for pulmonary function testing. tremoflo®is an oscillometer that measures resistance and reactance of small airways. SpiroScoutis an ultrasonic spirometer. We invite you to discover their advantages and why they are complementary tests.