Fowler's method, or the nitrogen washout method, is a way of measuring 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 vs. expired volume curve is obtained by increasing nitrogen concentration, from zero to the percentage of nitrogen in the alveoli. It 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.

[edit] See also

• Physiology
• Dead space

[edit] External links

• Google book
• Resp Physiology

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