Although breathlessness on exertion is one of the most common symptoms of disease, and though difficulty in obtaining a sufficient exchange of oxygen and carbon dioxide is the underlying cause, the exact mechanism is little understood. Certainly it is the quantity of air and of oxygen relative to the capacity of the subject rather than the absolute amount which is important, and we have tried to learn more about this phenomenon by comparing the reaction of normal and of breathless subjects to the same exercise.
The pioneer work of Haldane has led to an enormous amount of investigation during the last twenty years, and has been applied to the changes at the beginning and end of exercise by Krogh and Lindhard,1 by Campbell, Douglas and Hobson2 and, more recently, by Hill and his fellow workers.3 The changes at the beginning take place quickly, and the larger part of the reverse
CAMPBELL JMH, SALE FJ. EFFECT OF EXERCISE ON RESPIRATORY EXCHANGE IN HEART DISEASE. II. Arch Intern Med (Chic). 1927;40(2):237-250. doi:10.1001/archinte.1927.00130080111010