of the rate of instantaneous blood flow through the body section being tested application_number US 57447175 A description i propose to take into account the fact that the arteries of a living body are essentially ducts with elastic walls as the blood pressure varies during the cardiac cycle the diameters of the arteries may also vary and the flow of blood through the arteries has pulsatile character which results in periodic accumulation and decumulation of blood in the section of the body subject to test based on principles of the mechanics of viscous flow through ducts with elastic walls and the theory of elasticity i provide the following formula for the instantaneous rate of blood flow equ1 where q is the instantaneous rate of blood flow in cc per second e is the average modulus of elasticity of the arterial walls 10 6 dynes per square centimeter is a typical value k is the average ratio of outer to inner radii of the arterial walls a typical value of k is 1 1 u03bc is the viscosity of blood a typical value is 0 03 gm per centimeter per second s is the average speed of propagation of pressure through the arterial walls a typical value is 1000 centimeters per second r o is the average radius of the chest of a patient in centimeters measured on the patient u03c1 is the electrical resistivity of blood a typical value is 200 ohm centimeters l is the distance between the impedance measuring electrodes in centimeters measured on.