In accordance with the present trend of clinical medicine, there have been many attempts to devise methods for obtaining objective evidence concerning the functional condition of the heart in patients with cardiovascular disease. Such methods may be divided into two categories: (1) those which attempt to estimate the functional state of the heart at any given time, i. e., its ability to meet the routine demands of life, and (2) those designed to measure the cardiac reserve, i. e., the ability of the heart to meet emergency demands.
Most of the phenomena which have been observed under those methods have been the coincidental changes in the cardiovascular and respiratory systems, such as deviations from the normal in vital capacity, minute volume of respiration, venous pressure, minute volume of blood flow, circulation time, blood pressure and pulse rate. While these measurements within their limits of accuracy are of undoubted value in
KATZ LN, SOSKIN S, SCHUTZ WJ, ACKERMAN W, PLAUT JL. A "METABOLIC EXERCISE TOLERANCE TEST" FOR PATIENTS WITH CARDIAC DISEASEA FEASIBLE METHOD FOR USING THE EXCESS OXYGEN CONSUMPTION AND THE RECOVERY TIME OF EXERCISE AS CRITERIA OF THE CARDIAC STATUS. Arch Intern Med (Chic). 1934;53(5):710–723. doi:10.1001/archinte.1934.00160110079008