Assessment of peripheral hemodynamics using impedance plethysmography

Impedance plethysmography (IPG) is a safe, noninvasive method for measuring peripheral hemodynamics. The purpose of this article is to describe the IPG technique and its potential use by physical therapists in making hemodynamic evaluations. Impedance plethysmography requires the attachment of four circumferential Mylar band electrodes around a limb. We use a cardiograph to introduce a 4-mA current (I) at a frequency of 100 kHz in the two outer electrodes. The voltage (V) is sensed in the two center electrodes, and the resulting impedance (Z) is calculated using Ohm's law (Z = V/I). Arterial blood flow can be calculated using an impedance-related volume conduction equation. Impedance plethysmography has been shown to be economical, and any limb or limb segment can be evaluated. Applications are presented for the assessment of arterial blood flow, peripheral arterial disease, deep vein thrombosis, and venous insufficiency. Impedance plethysmography offers the physical therapist a safe and relatively simple technique to assess the peripheral vascular status of the patient.