title: Detection of air trapping in chronic obstructive pulmonary disease by low frequency ultrasound.
abstract: BACKGROUND
  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.
  
  
  METHODS
  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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
  
  
  BACKGROUND
  ClinicalTrials.gov: NCT01080924.
authors.affiliation: Institute for Pharmacology and Toxicology, Medical Faculty, RWTH Aachen University, Wendlingweg 2, 52074 Aachen, Germany. suhlig@ukaachen.de
authors.forename: Katrin
authors.initials: K
authors.lastname: Morenz
authors.forename: Heike
authors.initials: H
authors.lastname: Biller
authors.forename: Frank
authors.initials: F
authors.lastname: Wolfram
authors.forename: Steffen
authors.initials: S
authors.lastname: Leonhadt
authors.forename: Dirk
authors.initials: D
authors.lastname: Rüter
authors.forename: Thomas
authors.initials: T
authors.lastname: Glaab
authors.forename: Stefan
authors.initials: S
authors.lastname: Uhlig
authors.forename: Jens M
authors.initials: JM
authors.lastname: Hohlfeld
mesh_terms: D000328:Adult; D000368:Aged; D000403:Airway Resistance / Q000187:drug effects; D000420:Albuterol / Q000494:pharmacology*; D000704:Analysis of Variance; D001993:Bronchodilator Agents / Q000494:pharmacology*; D045853:Exhalation; D005260:Female; D005541:Forced Expiratory Volume / Q000187:drug effects; D006801:Humans; D001239:Inhalation; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D010993:Plethysmography, Whole Body; D029424:Pulmonary Disease, Chronic Obstructive / Q000000981:diagnostic imaging* / Q000188:drug therapy / Q000503:physiopathology*; D012115:Residual Volume / Q000187:drug effects; D012720:Severity of Illness Index; D014463:Ultrasonography
chemical_list: D001993:Bronchodilator Agents; D000420:Albuterol