The electrical impedance of pulsatile blood flowing through rigid tubes: an experimental investigation

Abstract

Small fluctuations present in an Impedance Cardiogram are often dismissed as noise, but may be due to unknown physiological origins. One such origin suggested in literature is the impedance variation induced by changes in red blood cell orientation during pulsatile blood flow. This study investigated the relationship between the impedance, velocity and acceleration of blood as it pulses during the cardiac cycle. This was achieved experimentally by pumping blood through rigid tubes in a mock circulatory system while measuring the impedance and velocity of the blood. Analysis of collected data confirms that impedance responds to changes in both velocity and acceleration. During acceleration, impedance and velocity are linearly related. However, during deceleration, it was found that the relationship between impedance and velocity is non linear. As velocity increases, the relationship becomes linear with a reducing slope. This indicates that for the same change in acceleration at low velocities, the impedance response is significantly larger than at higher velocities. Experimental data demonstrating these trends is presented for varied pulse rates (20 – 100 beats per minute), stroke volumes (20 – 60 ml) and systolic/diastolic ratios (50/50 – 30/70).