Maximum Breathing Capacity With Various Expiratory and Inspiratory Resistances (Single and Combined) at Various Breathing Rates

¹ From the National Institute of Arthritis and Metabolic Diseases, National Institutes of Health, Bethesda, Maryland

The maximum breathing capacity (MBC) has been determined with various expiratory and inspiratory resistances (singly and combined) at breathing rates of 4–196 per minute. A given resistance in the inspiratory duct reduced the MBC more than when it was in the expiratory duct. At low resistance levels, the combined resistances lowered the MBC little more than the inspiratory resistance alone. At higher resistance levels the effect of inspiratory and expiratory resistances were more nearly additive. The breathing rate at which the highest MBC occurred was lowered by increasing the resistance. Thus it was about 100 breaths per minute at the lowest resistance level and about 40 breaths per minute at the highest resistance level. The relationship was such that the tidal volume was the same at the highest MBC at each resistance level. The MBC increased rapidly over the lower breathing rates and fell off slowly at rates of over 120. Because a fourfold increase in the expiratory airway resistance lowered the MBC little, it was concluded that special low resistance testing equipment was not necessary for the normal subject.

Note:
with the assistance of Howard Brubach and Pierce Gardner