Evaluation of specific pick-ups and preamplifiers for the recording of heart vibrations.
Experiments have shown that pick-ups used for the recording of heart vibrations (apexcardiography, phonocardiography) can influence the vibrations of the soft tissue chest wall to which they are applied. This influence is most pronounced in the medium and high frequency range (10 . . . . . 1000 Hz). Owing to the mechanical loading effect of the pick-up on the chest wall, the vibrations are attenuated and distorted. This is also shown with respect to pure mass loading of the chest wall. The loading effect on the chest wall (coupling function) has been studied by us in the frequency-domain as well as in the time-domain on 6 normal subjects who were in the recumbent position. Typical parameters of the coupling function have been established in relation to mass loading. An empirical formula has been found for the degree of attenuation of the vibrations caused by the load. In order to perform these investigations, a special seismic pick-up FYSPac2 has been constructed which will load the tissue to a slight degree only. Its mass is 1 g and it has a flat frequency response up to 1 kHz and a high sensitivity (12 pC m-1s2). The problem of the vibration measurement on soft tissue is discussed here in its whole context: the loading effect of the pick-up, the sensitivity (and bandwidth) of the pick-up as well as the quality of the preamplifier as regards its transfer characteristics and its electronic noise level.(ABSTRACT TRUNCATED AT 250 WORDS)
D000669:Amplifiers, Electronic; D005069:Evaluation Studies as Topic; D006801:Humans; D007702:Kinetocardiography / Q000295:instrumentation*; D014159:Transducers