Coronary input impedance during cardiac cycle as determined by impulse response method.

The coronary arterial system was characterized by its input impedance determined in systole and diastole from impulse response functions in five dogs. The impulse response technique was verified on a known hydraulic system. A second confirmation was obtained on the circumflex artery: reflected pulses were correlated with site of reflections generated by occlusions. The impulse response indicates discrete reflections, superimposed on the tail of the response, resulting from diffuse reflections. Input impedance was calculated from Fourier analysis of the impulse response. Characteristic impedance was 1.0 +/- 0.2 X 10(9) Pa X s X m-3 (0.13 +/- 0.02 mmHg X ml-1 X min) and impedance at 0 Hz was 2.6 +/- 0.8 X 10(9) Pa X s X m-3. No significant differences between systole and diastole were found in both characteristic impedance and impedance at 0 Hz. It is concluded that the coronary system consists of a proximal part that can be described with the three-element windkessel and a distal part not seen by oscillatory pressure or flow perturbations, which depends on the phase of cardiac contraction.