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This thesis for a doctor's degree is divided into three parts. The first part describes the results of phonocardiographic studies of the heart of fifty pregnant and forty-nine nonpregnant women, arriving at the conclusion that no changes in the character or frequency of heart sounds attributable to gestation can be found. The second part gives a description of records of fetal heart sounds and furnishes data as to their duration, frequency, number of vibrations which form the first and second sound, and so on. In the third part the author discusses the hemodynamics in the fetus and in other periods of life, calculated on the basis of the aforementioned studies.
As to the technic, he prefers the direct method of recording heart sounds with Wiggers-Dean capsule and optical registration to the indirect, in which the sound is transformed into oscillations of an electric current and after a suitable amplification is
Estudios fonocardiográficos y hemodinámicos en embarazadas y fetos en los últimos tiempos del embarazo normal. JAMA. 1940;114(22):2243. doi:10.1001/jama.1940.02810220067026