The fourth heart sound was clearly recorded by using the signal averaging method. Furthermore, the simultaneous recording of the Doppler signal with the fourth heart sound was performed. Thus, it was demonstrated that the Doppler signal started after the P wave and followed by the fourth heart sound. In 2 cases, the effect of the double Master's test and taking a bath was studied on the computer averaged phonocardiogram. After the exercise, the amplitude of the fourth heart sound was increased, whereas after taking a bath it was almost unchanged. The above results show that the simultaneous recording of a computer averaged phonocardiogram and Doppler signal that is associated with cardiac activity can greatly facilitate the interpretation of small vibrations such as the fourth heart sound.
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