Abstract
Multiple breath inert gas wash out test is a new method for lung function testing, which can be performed in all age groups independent of the patient's active cooperation. The two most important outcome parameters obtained are functional residual capacity (FRC) as a measure of lung size and lung clearance index (LCI), which informs about patency of the most peripheral airways (from the 12th generation to the periphery).
The assessment of airway patency is based on ventilation inhomogeneity, making this test different from conventional methods such as spirometry and body plethysmography and making it more sensitive to the mild changes in peripheral airways. The higher sensitivity to early changes in the airways has been shown in many studies.
According to the inert gas used for wash out, are several modifications of this test are available. The two most common variants use nitrogen or sulphur hexafluoride.
Although both methods are based on the same principle, the technical details are different and the results (absolute values) are not interchangeable. The multiple breath inert gas wash out test can be used mainly in the follow-up of patients with chronic respiratory diseases such as cystic fibrosis, primary ciliary dyskinesia, bronchial asthma and some perinatal lung pathologies.
Thanks to its high sensitivity, it is possible to perform therapeutic interventions before less sensitive methods (spirometry, evaluation of the clinical status) indicate any deterioration. Because of the inherent high sensitivity to the most peripheral airway pathology, the test is able to detect mild functional changes in early stages of the disease.
Bearing in mind the possibility to test patients while asleep, inert gas wash out is a very attractive method for infant pulmonary function testing.