With an ultrasonic fetal heart detector, several low-frequency Doppler signals can be heard over the precordium. In normals, the characteristic pattern comprises atrial (a) ventricular systolic (β), and ventricular diastolic (8) components. During quiet breathing the β signal is usually loudest (β pattern), but on deep inspiration, lying, or squatting, the α signal predominates (α pattern). In atrial flutter or fibrillation the a signal disappears, and in some cases quivering noises (ψ signals) are audible. The Dopplercardiophone can also be useful at the bedside, in conjunction with the stethoscope, in elucidating gallop rhythm. Simultaneous recordings of the Doppler-cardiogram with electrocardiogram and phonocardiogram help to relate the signals to discrete cardiac events. The Doppler signals are probably mainly due to blood flow, movement of the heart wall, or both. The contribution of valve closure is relatively minor.
Abelson D. Ultrasonic Doppler Auscultation of the Heart: With Observations on Atrial Flutter and Fibrillation. JAMA. 1968;204(6):438–443. doi:10.1001/jama.1968.03140190020006
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