Journal of Applied Physiology, Vol 68, Issue 5 1875-1882, Copyright © 1990 by American Physiological Society
Significance of airway resistance for the pattern of breathing and lung volumes in exercising humans
C. M. Hesser, F. Lind and D. Linnarsson
Department of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden.
The effects of increased airway resistance on lung volumes and pattern of
breathing were studied in eight subjects performing leg exercise on a cycle
ergometer. Airway resistance was changed 1) by increasing the density (D)
of the respired gas by a factor of 4.2 and changing the inspired gas from
O2 at 1.3 bar to air at 6 bar and 2) by increasing airway flow rates by
exposing the subjects to incremental work loads of 0-200 W. Increased gas D
caused a slower and deeper respiration at rest and during exercise and, at
work loads greater than 120 W, depressed the responses of ventilation and
mean inspiratory flow. Raised airway resistance induced by increases in D
and/or airway flow rates altered respiratory timing by increasing the ratio
of inspiratory time (TI) to total breath duration. Furthermore, analyses of
the relationships between tidal volume and TI and between end-inspiratory
volume and TI revealed elevation of Hering-Breuer inspiratory volume
thresholds. We propose that this elevation, and hence exercise-induced
increases of tidal volume, can largely be explained by previous
observations that the threshold of the inspiratory off-switch mechanisms
depends on central inspiratory activity (cf. C. von Euler, J. Appl.
Physiol. 55: 1647-1659, 1983), which in turn increases with airway
resistance (Acta Physiol. Scand. 120: 557-565, 1984).
