Electric impedance cuff for the indirect measurement of blood pressure and volume elastic modulus in human limb and finger arteries

A new plethysmograph, the electric impedance cuff, was designed for the indirect measurement of blood pressure, volume elastic modulus E_v and compliance C_a in human limb arteries. This comprises a compression chamber filled with electrolyte solution and a tetrapolar electric impedance plethysmograph whose electrodes are placed inside the chamber; the former for controlling transmural arterial pressure P_t, and the latter for detecting total limb volume V_o, mean arterial volume \(\bar V_a \) and its variation ΔV_a. Systolic and mean arterial pressure in the upper arms, forearms and fingers were measured by detecting pulsatile impedance variation during the gradual (3–5 mm Hg per heart beat) increase (or decrease) in chamber pressure by the volume oscillometric technique. Diastolic and pulse pressure ΔP were calculated from these pressure values. Compliance C_a=ΔV/ΔP and volume elastic modulus \(E_v = \Delta P/(\Delta V_a /\bar V_a )\) were recorded at various P_t levels, controlled by the compression pressure. Although this is a kind of impedance plethysmograph, the volume change in a limb segment can be detected by this method without passing electric current through the limb.