CLINICAL STUDIES OF THE RESPIRATION

<h3>INTRODUCTION</h3> In an earlier paper¹in this series, observations were described on the production of dyspnea in normal subjects and in patients with cardiac disease by means of increasing amounts of carbon dioxid in the inspired air. It was found that patients with heart disease became dyspneic more easily than did healthy subjects, and this tendency seemed to depend largely on their inability to increase the depth of respiration in a normal manner. A few preliminary determinations showed that this inability to breathe deeply corresponded to a diminished vital capacity of the lungs as measured by the volume of the greatest possible expiration after the deepest inspiration. Since any condition which limits the possibility of increasing the minute-volume of air breathed must be an important factor in the production of dyspnea, it appeared worth while to undertake an extensive study of the vital capacity of the lungs in those diseases