Nitrogen washout (or Fowler's method) is a test for measuring anatomic

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in the lung during a respiratory cycle, as well as some parameters related to the closure of airways.

Procedure

A nitrogen washout can be performed with a single nitrogen breath, or multiple ones. Both tests use similar tools, both can estimate

functional residual capacity Functional residual capacity (FRC) is the volume of air present in the lungs at the end of passive expiration. At FRC, the opposing elastic recoil forces of the lungs and chest wall are in equilibrium and there is no exertion by the diaphragm ...

and the degree of nonuniformity of gas distribution in the lungs, but the multiple-breath test more accurately measures absolute

lung volumes Lung volumes and lung capacities refer to the volume of air in the lungs at different phases of the respiratory cycle. The average total lung capacity of an adult human male is about 6 litres of air. Tidal breathing is normal, resting breathin ...

. The following describes a single-breath nitrogen test: A subject takes a breath of 100% oxygen and exhales through a one-way valve measuring nitrogen content and volume. A plot of the nitrogen concentration (as a % of total gas) vs. expired volume is obtained by increasing the nitrogen concentration from zero to the percentage of nitrogen in the

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. The nitrogen concentration is initially zero because the subject is exhaling the dead space oxygen they just breathed in (does not participate in alveolar exchange), and climbs as alveolar air mixes with the dead space air. The dead space can be determined from this curve by drawing a vertical line down the curve such that the areas below the curve (left of the line) and above the curve (right of the line) are equal. Most people with a normal distribution of airways resistances will reduce their expired end-tidal nitrogen concentrations to less than 2.5% within seven minutes. Individuals with high resistance in their airways can take longer than seven minutes to remove all the nitrogen.

Parameters

A nitrogen washout can obtain the following parameters: *Closing volume (CV); the amount of air remaining in the lungs beyond that of the residual volume when the flow from the lower sections of the lungs becomes severely reduced or halts altogether during expiration as the small airways begin to close.thefreedictionary.com > closing volume
Citing: The American Heritage Medical Dictionary Copyright 2007 and Mosby's Medical Dictionary, 8th edition. 2009 *Closing capacity (CC), which equals CV + (

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- VC), with VC taken from the curve acquired from the nitrogen washout test.Interpretation model - compendium at Uppsala Academic Hospital. By H. Hedenström. 2009-02-04 As a reference, it should be 70% to 130% of what is the average value in the population, which, in turn, may vary with geographic location. *Mean slope of the alveolar plateau (phase III). It should be less than 175% of population average.LUNGFUNKTION - Practice compendium for semester 6. Department of Medical Sciences, Clinical Physiology, Academic Hospital, Uppsala, Sweden. Retrieved 2010. Also, from those values, additional parameters can be calculated: *CV/ VC ratio *CC/

ratio Both of the above should be less than 125% of population average.

References

External links

*Fowler's method in {{Respiratory physiology Medical tests Pulmonary function testing Respiratory therapy