Some requirements in equipment and technics for vectorcardiography.

To reduce the effects of extraneous potentials caused by muscle tremor, sweating, and interference from power circuits, it is desirable to restrict the frequency range of the cathode ray vectorcardiograph. Mathematical analysis of idealized waves and experiments with a photoelectric electrocardiographic generator indicate that a frequency range between the half-power frequency of 0.8 to 80 cycles per second is satisfactory for proper reproduction of most vectorcardiograms. Many investigators construct the vectorcardiogram graphically from the electrocardiogram. In this study it is shown that, unless simultaneous electrocardiograms recorded at greater than usual paper speed are used, such vectorcardiograms may be incorrect. D URING the past six years the attention of cardiologists in increasing numbers has been directed toward vectorcardi-ography. This attention has been stimulated by the hope that this phase of electrocardiog-raphy may lead to new information of clinical importance in detecting and evaluating heart disease and of physical importance in determining the manner in which electric currents are generated by the living heart and propagated through the body. Modern electrocardiography and vector-cardiography are intimately associated with vacuum tube amplifiers and oscillators, cathode ray oscilloscopes, and electronic timing circuits. Although the Einthoven string galvan-ometer is satisfactory for electrocardiography, modern automatic vectorcardiography would be impossible without the vacuum tube amplifier and the cathode ray oscilloscope. Theoretically the combination of vacuum tube amplifiers and cathode ray tubes should constitute the perfect vectorcardiograph. With this system the amplifier alone is the limiting factor in both low-and high-frequency reproduction. With a suitable direct-coupled amplifier all of the frequencies encountered in vec-torcardiography may be reproduced properly. direct-coupled amplifier having the required voltage gain of approximately 200,000 is difficult to construct and maintain. Moreover, the effects of extraneous voltages due to sweating at the electrode sites, both low-and high-frequency skeletal muscle activity, respiration , changes in the position of the subject, and inductive and electrostatic interference from adjacent power circuits and electrical equipment make it advisable to restrict as much as possible both the low-and high-frequency limits of the vectorcardiograph. A theoretic study was made to determine the approximate frequency requirements for a satisfactory vectorcardiograph. In addition, a photoelectric generator was constructed which could produce voltages similar in waveform to those encountered in vectorcardiography. With the generator, it was possible to demonstrate some of the errors which may occur when the vectorcardiogram is constructed graphically from standard electrocardiograms, and to determine bv means of frequency attenuating networks the …