The term functional capacity is used to indicate the total amount of power possessed by the heart muscle. When the body is at rest a small portion of this power is utilized to furnish the circulatory requirements of the metabolism. As soon as any muscular activity occurs the so-called reserve power of the heart is drawn on to furnish blood to the working muscles.
Of these two component parts of the power inherent in the heart muscle the reserve power forms normally by far the larger portion, and it is with this factor that our studies are concerned. We propose to gain an idea of the heart's functional capacity by a measurement of its reserve power.
The method used to determine this is based on the circulatory reactions to graduated work, and a rather detailed description of these reactions is necessary to a clear understanding of our test, and, what
BARRINGER TB. STUDIES OF THE HEART'S FUNCTIONAL CAPACITY. Arch Intern Med (Chic). 1917;XX(6):829-839. doi:10.1001/archinte.1917.00090060003001