Three-block electrical model of renal impedance.

In this study, we measured the characteristic renal impedance profiles of Wistar rats and simulated the profiles using an electrical model with three series connected Windkessel blocks containing inductance. It is expected that a complete renal impedance profile ought to provide better physical properties information and have more diagnostic power than the pulsatility (PI) and resistive indices (RI) as a result of frequency dependency. A characteristic peak value at the third harmonic on the renal impedance amplitude curve was observed and the phase curve decreased with increasing harmonic numbers. From least mean square fitted parameters, the three blocks were given distinct physical properties and identified as: (1) the renal artery, (2) the small arteries plus the afferent arteriole and (3) the residual kidney (i.e., the efferent arteriole plus the post glomerular capillary structures). These allocations were made according to respective physical properties reported in previous research. These classifications were further confirmed when we compressed the kidney or infused Ang II. Variations in electrical parameters concurred with the likely affected blood vessels reported. This model describes renal impedance characteristics well; and it provides useful hints on the physical properties of the renal vascular system as well as allows for distinctions in possible physiologically affected locations during functional disturbance. It has potential for development as a clinical non-invasive diagnostic tool.