Tetrapolar impedance plethysmograph for assessing peripheral venous congestion.

BOLOGNINI, PATRICIO CARLOS; GOY, CARLA BELÉN; GOMEZ LOPEZ, MARIA DE LOS ANGELES; HERRERA, MYRIAM CRISTINA

Mar del Plata

Congreso; XVIII Congreso Argentino de Bioingeniería, VII Jornadas de Ingeniería Clínica; 2011

Sociedad Argentina de Bioingeniería

It has been suggested that venous congestion would be an independent and fundamental stimulus for the onset of decompensated cardiac heart failure. Early detection of congestion could be assessed by venous occlusion plethysmography. In this context, we propose to develop a tetrapolar impedance plethysmograph and method for evaluating the drain venous capacity after a 60sec cuff occlusion by analyzing changes in impedance. Occlusion maneuver avoids venous return; therefore, blood accumulates in lower limbs changing its impedance. The device comprises of a 50KHz stabilized current generator that provides a sinusoidal current of 2mA. The current flows through the limb to produce an amplitude modulated voltage which is appropriately amplified and filtered. Then, the signal is demodulated and stored using a ?sample and hold? circuit. Finally, the basal impedance is separated from impedance variations due to volume changes by means of a suppression circuit. The whole plethysmograph has proven to be highly linear (R2 = 0.998) while the current shows stability in repeated measurements with different loads (from 6 to 412 Ω). Frequency response curve shows a typical low-pass pattern with a cut-off frequency of 7Hz. Finally, as an example, a temporary record of an occlusive maneuver in a healthy volunteer is presented.