Physiological Observations During Induced Dyspnea

Abstract

In 17 iiormal subjects, dyspiiea was induced by exercise at 500 Kg.-M. per minute, with added external airway resistance. Arterial blood gas tensions and p transpulmonary I)reSsure, and pulmonary ventilation were measured iii the control period, at the onset of dyspnea, and at the disappearance of dysp ilea, which followedi cessation of exercise. Close correlation of the symptom with the functions measured was obtained through the use of hand signals by the subject to denote the onset and disappearance of ally unpleas ant sensation. The meaning of the signals was later obtained liv description. Except for a difference in time required for the devel opment of dyspnea, the results were similar whether the subject was exercised in the Su pine or in the 65-degree head-up position. In every instance, while the subjects were breath ing air, at the time of appearance of dyspnea, the arterial oxygen tension had fallen below control, levels, and at the disappearance of the symptom, the oxygen tension had returned to or near the control value. No such correla tion was obtanieci between the symptom mid the other variables measured. Subjects who did not develop dyspnea showed no fall ill arterial oxygen tension. The subjects exer (Ismg while breathing 100 per cent oxygen required longer periods for the development of dyspnea, and six of eight subjects who de veloped clysl)llea while breathing air experi enced partial Or complete relief of dyspnea despite the continuance of exercise when, un known to them, the inspired gas was switched from air to 1.00 Per cent oxygen. These resuggest that dyspnea, under the conditions of these experiments, was related to the sum- mated load of respiratory stimuli. In these experiments, the arterial oxygen tension ap pareritly was the critical variable.