Frequency Modulation of Heart Rate to Increase Low-Frequency Content of Cardiovascular Signals

Vital physiologic infonnation about the cardiovascular system resides in the low-frequency range of the frequency spectrum. The regularity of cardiac pulsations generaily restricts their frequency spectrum to a few lines corresponding to the hannonics of the regular wave-forms with little or no information at frequencies below the natural heart rate. To obtain accurate infonnation at frequencies above zero but below the natural heart rate, a simple experimental technique has been developed which introduces a periodic perturbation to the heart rate by electrical pacing. This frequency-modulated heart rate results in predictable increases in the low-frequency content of the pressure (F) and flow (Q) signals corresponding to the period and associated harmonics of the perturbation. Using this technique, curves are plotted for the modulus of the low-frequency hydraulic input impedance of a canine systemic arterial system.