The Harmonic Analysis of Intraventricular Pressure Curves

Investigators who have devised practical forms of manometers recording by optical registration have experienced considerable difficulty in selecting the constants so that an adequate natural frequency and a sufficient degree of sensitivity exist at the same time. Frank’s equation 2’ = M 1 2R ---y iE makes it clear why this is so. The natural period, T, is decreased by reducing the effective mass, M’, or by increasing the volume elasticity coefficient, E’. There are practical limits, however, beyond which the effective mass cannot be reduced and yet retain a practical form of instrument. There is likewise a limit beyond which E’ cannot be increased without reducing the ratio between pressure changes in the cardiovascular system and amplitude of record, i.e., the sensitivity. Adequate amplitude is, however, almost as important as accurate amplitude and contour; without it, smaller oscillations or bends are often difficult to locate with precision, and tie vibrations are entirely obscured when pressure gradients are steep. In membrane manometers, the inverse relation between natural frequency and sensitivity is easily altered by changing the thickness and tension of the rubber membrane. This is illustrated by the following data derived from tests with an optical manometer. devised by the author: In cardiodynamic researches reported at various times, the writer has taken care that manometers with all three of these ratings were employed in different experiments of the same series, and, in this way, curves recorded with different ordinate values were at his disposal. Most of the published intraventricular pressure curves were obtained with manometers having a natural frequency of about 180, and a sensitivity ratio of 3.5: 10; and, as a matter of fact, they have proved the most valuable for analysis. In the study of right ventricular and pulmonary pressures, the most satisfactory curves were obtained by manometers whose sensitivity was 6: 10, and whose natural frequency was about 150 per second. It becomes desirable, however, to reinvestigate the adequacy of