Some Factors Determining the Maximum Breathing Capacity

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

Maximum breathing capacity (MBC) predicted from the fast vital capacity (FVC) curves increases with increasing breathing rates. Experimentally determined data, however, indicate that the MBC increases with increasing breathing rates only to a point (determined by airway resistance level) after which it decreases. This deviation is most likely due to a minute volume deficit due to flow reversal in going from inspiration to expiration and vice versa. It has also been shown that one can reasonably predict the MBC from the FVC curves with high external airway resistances. A similar volume deficit due to flow reversal was also noted here but the prediction error was less (if breathing rate of peak observed MBC was known) because of the smaller volume moved per breath and also because of the smaller volume loss per breath multiplied by fewer breaths per minute. In addition, data have been collected showing the interrelations of airway resistance, breathing rate and maximum breathing capacity.