Body plethysmography

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Plethysmograph Plethysmography can accurately demonstrate lung conditions not measured by simple spirometry.

Body plethysmography is a very sensitive lung measurement used to detect lung pathology that might be missed with conventional pulmonary function tests. This method of obtaining the absolute volume of air within one's lungs may be also be used in situations where several repeated trials are required or where the patient is unable to perform the multibreath tests. The technique requires moderately complex coaching and instruction for the subject. In the USA, such tests are usually performed by Certified or Registered Pulmonary Function Technologists (CPFT or RPFT) who are credentialed by the National Board for Respiratory Care NBRC [1].

More specifically, the test is done by enclosing the subject in an airtight chamber often referred to as a body box; a pneumotachometer is used to measure airflow while a mouth pressure transducer with a shutter measures the alveolar pressure. The most common measurements made using body plethysmographs are thoracic gas volume (VTG) and airway resistance (R_AW). This test is used mainly in the Pulmonary Function Testing laboratories.

Using body plethysmography, doctors can examine the lungs' resistance to airflow, distinguish between restrictive and obstructive lung diseases, determine the response to bronchodilators, and determine bronchial hyperreactivity in response to methacholine[[2]], histamine, or isocapnic hyperventilation.

[edit] Flow and Pressure Plethysmographs

Plethysmograph A person is entirely enclosed within the body box space, the door sealed, pressure equilibrated, and measurements taken. With high visibility and intercom communication with the pulmonary function technologist, the subject has less risk of fearing the test.

There are two types of plethysmographs: flow and pressure. In flow plethysmography, airway resistance is measured by two maneuvers. The patient first pants while the mouth shutter is open to allow flow changes to be measured. Then, the mouth shutter closes at the patient's end expiratory or FRC level and the patient continues panting while maintaining an open glottis. This provides a measure of the driving pressure used to move air into the lungs.

Pressure plethysmographs are usually measured at the end-expiratory level and are then equal to FRC. The patient sits in the box, which has the pressure transducer in the wall of the device, and breathes through a mouthpiece connected to a device that contains an electronic shutter and a differential pressure pneumotachometer. The mouth pressure and box pressure changes that are measured during tidal breathing and panting maneuvers which are performed during the test by the patient at the end of expiration are sent to a microprocessor unit that calculates thoracic gas volume.

[edit] References

[edit] See also

• Plethysmograph