A Study of the Mechanical Impedance to Flow in the Femoral Peripheral Vascular Bed of the Dog

The mechanical impedance to blood flow in the hind limb of the dog was studied, and a dynamic relationship among the various factors affecting blood flow was derived. The blood flow through the femoral artery was routed through external polyethylene tubing containing an electromagnetic flowmeter and a Statham pressure transducer. The pulsatile blood pressure and the blood flow were displayed simultaneously on a dual-beam oscilloscope and recorded on 35-mm film. The pressure and the flow curves were then analyzed for their respective Fourier component frequencies. The Fourier analysis was performed with a frequency converter and a wave analyzer. The mechanical impedance is calculated by dividing the amplitude of each pressure harmonic by the amplitude of the corresponding flow harmonic. The average mechanical impedance vs. frequency curve has two resonant frequencies: one between 3.6 and 4.6 cps and the other between 5.6 and 7.0 cps. The impedance has a minimum value of about 1.2 peripheral resistance units at each resonant frequency. The flow vs. frequency and the pressure vs. frequency curves are also described. A theoretical electrical analog is hypothesized. This circuit consists of two arms in parallel, each arm containing an inductance and a resistance in series with a parallel capacitance and resistance. The impedence equations for the analog circuit are derived, and the impedancefrequency curve of the circuit is qualitatively constructed. This constructed curve agrees with experimental observation. The dynamic relationships existing among the elastance, inertial, and frictional factors affecting blood flow are discussed. (auth)