Breathing Reserve: What is it, how is it calculated?

Breathing Reserve (BR) is usually determined during a pulmonary exercise stress test. It is the difference between the maximal voluntary ventilation (MVV) and the maximum ventilation measured during the exercise test.

Normal males have a breathing reserve of 15 liters per minute or 20 to 40% of the MVV. (Wasserman et al)

Some experts do not believe direct MVV measurement to be reliable because it is very effort dependent and is very difficult to put acceptability criteria together. However, FEV1 is well defined, when and how is it acceptable. Therefore, it is a fairly well-defined measure that can be used to predict the MVV.

The formula for MVV, when derived from FEV1 is 40 * FEV1 or some are using 35 * FEV1.

Calculation: BR (L/min) = MVV - Max VE.

BR% = (MVV - VE / MVV) x 100.

Example: If MVV = 82 L/min and
VE at max exercise is 65 L/min,

Then:

BR = 82 - 65 = 17

BR% = (82 - 65 / 82) x 100 = 21%

Last update: 11/1/08