Combined impedance plethysmography and spectroscopy for the diagnosis of diseases of peripheral vascular system

Aim of this paper is to present a combined impedance plethysmography and spectrometry technique suitable to measure the functionality of the peripheral vascular system, with emphasis on the lower limbs. The plethysmographic investigation allows studying the venous flow by detecting the change in blood volume through an electrical bio-impedance measurement. In particular, such measurement is based on a procedure that does not require the use of an occlusive cuff that might cause a detachment of potential thrombus because of the downstream venous pressure. The spectroscopic investigation, instead, might reveal possible differences in the limb impedance spectrum due to a different resistivity of flowing blood as compared to standing blood: the latter, in particular, might be present in case of vascular diseases. Results obtained on healthy subjects show an increasing impedance in correspondence of blood volume decreases forced by a rise of the limb, and a corresponding decrease in the impedance linked to the leg blood filling as the limb is taken back to its rest position. The two transitions follow an exponential trend with different time constants. For a healthy patient, the bio-impedance of the leg shows a comparable behavior between the two legs, while for a subject with venous thrombosis a longer transient is expected for the affected limb. Similarly, the impedance spectrum of healthy patients shows almost the same frequency behavior for both legs, while possible differences might be detected in case of thrombosis.