Abstract
Dyspnea from muscular exercise results when the increased respiratory demands can no longer be met without effort. In the present series of experiments the ability to meet these demands was artificially restricted by having a normal individual (A. W. H.) breathe through small apertures. For this purpose two perforated corks were used, the diameters of the bores being 8 mm. and 6 mm. respectively. The first of these caused no effort so long as the subject of the experiments was at rest. It caused moderate respiratory effort when stairs were climbed at the rate of approximately 80 per minute. The second caused slight effort at rest and considerable distress during stair climbing. The latter culminated in discontinuance of the exercise after two or three minutes.
During rest, the respiratory rate was not influenced by the milder obstruction but in some experiments was somewhat slowed by the more marked obstruction. During exercise, the respiratory rate was definitely slowed by each, average figures being: without stenosis 27 respirations per minute, with 8 mm. stenosis 21 respirations per minute, and with 6 mm. stenosis 17 respirations per minute.
During rest, the minute volume of respiration was not altered by the lesser stenosis but in some experiments became somewhat less with the more marked stenosis. During exercise, the minute volume was regularly reduced. After one to three minutes of exercise pulmonary ventilation became approximately constant at the following levels: without stenosis 52 liters per minute, with 8 mm. stenosis 46 liters per minute, and with 6 mm. stenosis 28 liters per minute. With the more marked obstruction, stair climbing had to be discontinued after 2 to 3 minutes on account of increasing distress. With the less marked obstruction this was not the case. Compensation for the restricted ventilation was here accomplished by increasing the percentage of O2 absorbed from and of C02 given off to the respired air.
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