Fundamental frequency modulation of the human voice by the heartbeat: preliminary results and possible mechanisms.

Signal-averaging techniques reveal that the vocal fundamental frequency (F0) of a sustained vowel is modulated over a period equal to that of the speaker's heart cycle. Average F0 deviation varies in an orderly way from about 0.5% to about 1.0% as F0 changes. Location of the peak deviation in the time frame of the heart cycle also changes systematically with vocal F0. Modulation of the vocal F0 is likely to be caused by pressure-related changes in the stiffness of the vascular bed of the vocal folds and by alterations of the geometry of the thyroarytenoid muscle produced by periodic vascular engorgement.