Abstract
In order to study low-frequency cardiac vibrations less than 20 cps, the vibration at various points within the esophagus has been recorded by a strain-gauge transducer connected with a water filled No.13 cardiac catheter whose end was coveredby a small rubber balloon.
The curves of the vibrations recorded by this method were found to be greatly affected by the mode of tubing systems. Thus, for the purpose of an accurate analysis of the curves, the frequency and transient response characteristics of the tubings and the timing delay due to transmission of the pressure in the tubings were studied by application of the sine-wave and square-wave pressure vibrations under various conditions. Results were as follows : The resonant frequency of the transducer and amplifier without tubings was 95 cps and the response curve was flat up to 80 cps. The resonant frequency became lower and the damping effect or the transmission time of the pressure increased in proportion to the length as well as the narrowness of the catheter. These tendency were more remarkable in the case of a polyvinyl tube. When stopcocks or a lead tube were inserted between the catheter and transducer, the resonant frequency decreased but the transmission time a little increased. The range of resonant frequency of the present study was 6-27 cps, the damping ratio 0.06-0.33, and the transmission time 5-16 msec.
When a three-way stopcock and a lead tube of 40 cm length were inserted between the transducer and No. 13, 120 cm catheter, the resonant frequency was 12 cps, responses over 20 cps greatly attenuated and the ransmission time was 7 msec. Therefore, this tubing seemed to be desirable, practicable in the intraesophageal recording.
