Methods of functional diagnosis should comply with two requirements: The function to be tested should be precisely known, and quantitative results should be obtained. Neither of these has been exactly fulfilled by the existing methods of functional diagnosis of the heart, first, because the exact nature of the function tested is not given and, second, because the results are not quantitative. In this paper, attention is called to the possibility of elucidating one definite function of the heart by the means of certain graphic methods, phonocardiography and sphygmography. I call these cardiodynamic records. This function, the tonicity, can be considered to depend on the isometric contraction of the myocardium, as expressed in its time element. I will try to bring out some facts in favor of this assumption, after pointing out some well known experimental data on which the hypothesis is based.
Two different forms of contraction occur
D'IRSAY S. THE VALUE OF CLINICAL CARDIODYNAMIC RECORDS. Arch Intern Med (Chic). 1925;36(1):62-72. doi:10.1001/archinte.1925.00120130065007