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Diffusing Capacity and Barometric Pressure Adjusted for Altitude

Purpose: To correct the diffusing capacity seen at high altitudes to that expected at sea level in order to adjust for the increase from the lower inspired oxygen pressure.

Description

Since the composition of inspired air is affected by altitude, the observed diffusing capacity seen at a certain altitude needs to be adjusted to sea level in order to allow accurate interpretation of the results.


altitude adjusted diffusing capacity =

= (measured capacity) * (1.0 + (0.0031 * ((alveolar PO2) - 120)))

=  (measured capacity) * (1.0 + (0.0031 * ((0.21 * (Pbar -47)) - 150)))

 

where:

• 150 mm Hg is the inspired oxygen pressure at sea level

• Pbar = barometric pressure at the altitude

• Diffusing capacity is reported in mL of CO (at STPD) per minute per mm Hg.

 

If the barometric pressure is not known, it can be estimated as

 

barometric pressure in mm Hg =

= 760 * ((1 - (0.000006873 * (altitude above sea level in feet))) ^ 5.256)


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Specialty

Objective

ICD-10