EBME & Clinical Engineering Articles

Impulse Oscillometry (Lung Function) Systems - IOS

Detecting lung diseases with sound waves.

valvesHospital scientists are using sound waves to detect airway changes in patients with severe lung conditions.

Impulse oscillometry (IOS) was introduced at Birmingham's Queen Elizabeth Hospital to tackle problems associated with conditions like chronic obstructive pulmonary disease (COPD) and asthma.

Computer-aided IOS enables clinicians to detect subtle changes in a patients airway function earlier than when using conventional and more expensive techniques.

vmaxAs the patient breathes through a pneumo-tachograph, a sound wave generated by a loudspeaker is superimposed over their breathing. The patients airflow and sound wave response is transmitted to the apparatus and used to calculate the various components of resistance to breathing.

Currently, this innovative technique has produced excellent results in clinical services both for patients who have received lung transplants and for those with severe airways disease.

The procedure's benefits include:

  • Nothing more than quiet breathing is required from the patient - compared to other methods which can be invasive and unpleasant to the patient.
  • Categorising the severity of a condition without the need for complex or expensive procedures requiring scans, invasive tests or radioisotope markers.
  • Potential for developing the technique for use either in the GP surgery or even the patients home.

Objective lung function measurements are routinely used to diagnose and manage asthma, but their utility for young children has not been defined.

In one American study, Bronchodilator responses were measured using impulse oscillometry (IOS) and compared with conventional spirometry to determine the value of lung function measures in 4-year-old asthma-prone children.

vmax systemThe study participants were in the Childhood Asthma Prevention Study (National Institute of Health/National Institute of Allergy and Infectious Diseases) and at risk for asthma. At age 4 years, concurrent asthma was determined by using a previously validated modified American Thoracic Society questionnaire. Children performed IOS and spirometry before and after albuterol administration and underwent skin prick testing to 13 common allergens to assess atopy.

IOS bronchodilator responses are remarkably abnormal in 4-year-old children, who are most likely to have persistent asthma. IOS is a useful diagnostic tool in early asthma development and might be a helpful objective outcome measure of early interventions. (J Allergy Clin Immunol 2003;112:317-22.)

Pulmonary Function Tests

(This functionality will vary with different devices)


  • Single button activation, Independent selection of best inspiratory and expiratory maneuver, Partial flow/volume loops

Lung Volumes by Nitrogen Washout

  • No nitrogen analyzer (no pumps, needle valves, oil changes, or noise), Automated leak detection, Lung clearance index, Washout pattern - "Shape Profile", interpretation (slow/fast emptying), Closing volumes (SBO2)

Diffusing Capacity, Single Breath

  • Real-time gas measurement to ATS/ERS recommended standards, Adjustment of discard and sample volumes, Integrated airway pressure monitoring during breath-hold, Lung Volumes determination, Test more patients - Testing capability for patients with low lung volumes.

Diffusing Capacity, Intra-breath (NON-BREATH HOLDING)

  • Alternative for dyspneic patient who can't hold their breath for 10 seconds, Exercise diffusion testing, Non-Invasive Cardiac Output (NICO) measurement*


  • Closing Volumes and Delta N2, Anatomical Dead Space


  • Thoracic Gas Volume, panting or quiet breathing, Airways Resistance, panting or quiet breathing, Display individual and composite tracing, Adjustable quiet-breathing compensation

Compression Free F/V Loops

  • Easily differentiate upper airway obstruction from poor patient effort, Monitor compression volume shifts

Bronchial Challenge

  • Complete user-defined protocols, Pre, Baseline plus 16 levels per protocol

Respiratory Mechanics Test

Inspiratory and Expiratory Pressures

  • View pressures at various lung volumes, Trans-diaphragmatic pressures, Compliance, Work of breathing.



Vmax Encore PFT
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Detecting lung diseases with sound waves.