IMPROVED METHOD FOR THE DETERMINATION OF THE PULSE TRANSMISSION CHARACTERISTICS OF ARTERIES INVIVO

On the basis of the theory of wave transmission lines, an improved method is described which permits the determination of the complex propagation coefficient of arteries from the Fourier components of natural pressure pulses. This coefficient is composed of the damping constant (α) and the phase constant (β). In the arterial system, there is always a superposition of forward- and backward-traveling waves, the interrelationship of which is not known to the investigators. Therefore, we have to deal with an additional unknown, and at least three independent measurements are necessary. Previous methods required recordings of three or four variables, such as pressure, flow, and/or diameter. In the new procedure, only two recordings of pressure are needed. This is made possible by occluding the artery directly behind the distal measuring point so that total positive reflection occurs and a defined relationship between forward and backward waves is brought about. This method is applied in the common carotid arteries of nine dogs. By the additional recording of the arterial diameter by means of a photoelectric device, the characteristic impedance (Z) is also determined. For the frequency range of 1.25-12 Hz, α was found to increase from 0.003 to 0.01 Neper/cm, and β from 0.02 to 0.1 radian/cm. The phase velocity was 9-11 m/sec. The modulus of Z was between 7,000 and 12,000 CGS units and dropped slightly with increasing frequency. The results are compared with those of other authors, and the accuracy of the various methods is discussed.