Nitrogen washout

Nitrogen washout (or Fowler's method) is a test for measuring dead space 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 and the degree of nonuniformity of gas distribution in the lungs, but the multiple-breath test more accurately measures absolute lung volumes.^[1] 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 alveoli. 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) area 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 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.^[2]
• Closing capacity (CC), which equals CV + (TLC - VC), with VC taken from the curve acquired from the nitrogen washout test.^[3] As a reference, it should be 70% to 130% of what is the average value in the population,^[4] 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.^[4]

Also, from those values, additional parameters can be calculated:

• CV/VC ratio
• CC/TLC ratio

Both of the above should be less than 125% of population average.^[4]

See also

• Physiology
• Dead space

References

1. ^ Newth, C. J. L.; Enright, P.; Johnson, R. L. (1997). "Multiple-breath nitrogen washout techniques: including measurements with patients on ventilators". European Respiratory Journal 10 (9): 2174–2185. doi:10.1183/09031936.97.10092174. PMID 9311523.  edit [1]
2. ^ thefreedictionary.com > closing volume Citing: The American Heritage Medical Dictionary Copyright 2007 and Mosby's Medical Dictionary, 8th edition. 2009
3. ^ Interpretation model - compendium at Uppsala Academic Hospital. By H. Hedenström. 2009-02-04
4. ^ ^{a b c} LUNGFUNKTION - Practice compendium for semester 6. Department of Medical Sciences, Clinical Physiology, Academic Hospital, Uppsala, Sweden. Retrieved 2010.

External links

• Google book
• Resp Physiology

This science article is a stub. You can help Wikipedia by expanding it.v · Categories: Medical tests Pulmonary function testing Respiratory therapy Science stubs Wikimedia Foundation. 2010. Игры ⚽ Нужно решить контрольную? Hypothetical types of biochemistry Nuclear magnetic resonance spectroscopy of proteins Look at other dictionaries: nitrogen washout test — (for functional residual capacity of lungs) with the patient inhaling pure oxygen, the concentration of exhaled nitrogen is obtained for each breath until it falls below 1 per cent of the gas being exhaled (usually about seven minutes time); the… …   Medical dictionary nitrogen washout test single breath — the patient inhales a vital capacity s volume of pure oxygen and then slowly exhales. The nitrogen concentration of the exhaled gas is measured over the entire breath and a curve is generated; different parts of the curve represent nitrogen… …   Medical dictionary nitrogen washout — see under test …   Medical dictionary Spirometry — TLC Total lung capacity: the volume in the lungs at maximal inflation RV Residual volume: the volume of air remaining in the lungs …   Wikipedia Perfluorocarbon — derivatives are perfluorocarbons with some functional group attached, for example perfluorooctanesulfonic acid. Perfluorocarbon derivatives can be very different from perfluorocarbons in their properties, applications and toxicity.The term… …   Wikipedia Oxygen toxicity — Classification and external resources In 1942–43 the UK Government carried out extensive testing for oxygen toxicity in divers. The chamber is pressurised with air to 3.7  …   Wikipedia Fowler method — Fowler s method, or the nitrogen washout method, is a way of measure dead space in the lung during a respiratory cycle. A subject takes a breath of 100% oxygen and exhales through a one way valve measuring nitrogen content and volume. A nitrogen… …   Wikipedia Dead space (physiology) — Blood gas, acid base, gas exchange terms PaO2 Arterial oxygen tension, or partial pressure PAO2 Alveolar oxygen tension, or partial pressure PACO2 Arterial carbon dioxide tension, or partial pressure PaCO2 Alveolar carbon dioxide tension, or… …   Wikipedia Hemoglobin — Hemoglobin, human, adult (heterotetramer, (αβ)2) Structure of human hemoglobin. The protein s α and β subunits are in red and blue, and the iron containing heme groups in green. Fro …   Wikipedia Breathing — Breath redirects here. For other uses, see Breath (disambiguation). For other uses, see Breathing (disambiguation). The human respiratory system Breathing is the process that moves air in and out of the lungs. Aerobic organisms require oxygen to… …   Wikipedia 18+ © Academic, 2000-2024 Contact us: Technical Support, Advertising Dictionaries export, created on PHP, Joomla, Drupal, WordPress, MODx. Mark and share Search through all dictionaries Translate… Search Internet Share the article and excerpts Direct link … Do a right-click on the link above and select “Copy Link”