Resonance in the kidney system of rats

The pressure wave of the abdominal aorta and the flow wave of the renal artery were recorded simultaneously from a rat. The impedance of a kidney system that is derived by dividing the pressure of the corresponding frequency by that of the flow was studied in six rats. The data show that the system has two resonant frequencies, at the second and third harmonics. At the second harmonic, the pressure wave and fluid flow in a round trip through the branch of the kidney. Whereas it is difficult for the third harmonic flow to enter the kidney, it flows directly through the aorta. To obtain further proof, we compared the frequency components of the two flows measured simultaneously on the abdominal aorta and the renal artery and found the same result. The kidney, renal artery, and aorta combined show a coupled oscillation that is analogous to that of resonance circuits. The kidney vascular system exhibits a resonant frequency at the second harmonic of the heartbeat.