Open Access Research article

Detection of air trapping in chronic obstructive pulmonary disease by low frequency ultrasound

Katrin Morenz1, Heike Biller2, Frank Wolfram13, Steffen Leonhadt3, Dirk Rüter4, Thomas Glaab5, Stefan Uhlig1* and Jens M Hohlfeld2

Author Affiliations

1 Institute for Pharmacology and Toxicology, Medical Faculty, RWTH Aachen University, Wendlingweg 2, 52074 Aachen, Germany

2 Fraunhofer Institute for Toxicology & Experimental Medicine (ITEM), Department of Clinical Airway Research, Nikolai-Fuchs-Str. 1, 30625 Hannover, Germany

3 Philips Chair of Medical Information Technology, RWTH Aachen University, Pauwelsstraße 20, 52074 Aachen, Germany

4 Institute for Measurement and Sensor Technology, Mülheim University of Applied Science, Wiesenstraße 36, 45473 Mülheim an der Ruhr, Germany

5 Boehringer Ingelheim, Medical Affairs, Respiratory, Binger Straße 173, 55216 Ingelheim, Germany

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BMC Pulmonary Medicine 2012, 12:8  doi:10.1186/1471-2466-12-8

Published: 16 March 2012



Spirometry is regarded as the gold standard for the diagnosis of COPD, yet the condition is widely underdiagnosed. Therefore, additional screening methods that are easy to perform and to interpret are needed. Recently, we demonstrated that low frequency ultrasound (LFU) may be helpful for monitoring lung diseases. The objective of this study was to evaluate whether LFU can be used to detect air trapping in COPD. In addition, we evaluated the ability of LFU to detect the effects of short-acting bronchodilator medication.


Seventeen patients with COPD and 9 healthy subjects were examined by body plethysmography and LFU. Ultrasound frequencies ranging from 1 to 40 kHz were transmitted to the sternum and received at the back during inspiration and expiration. The high pass frequency was determined from the inspiratory and the expiratory signals and their difference termed ΔF. Measurements were repeated after inhalation of salbutamol.


We found significant differences in ΔF between COPD subjects and healthy subjects. These differences were already significant at GOLD stage 1 and increased with the severity of COPD. Sensitivity for detection of GOLD stage 1 was 83% and for GOLD stages worse than 1 it was 91%. Bronchodilator effects could not be detected reliably.


We conclude that low frequency ultrasound is cost-effective, easy to perform and suitable for detecting air trapping. It might be useful in screening for COPD.

Trial Registration NCT01080924

Bronchodilation; Pulmonary function test; Diagnosis; GOLD