Proposed methods for the measurement of regional renal blood flow using heat transfer analysis

Abstract

The kidney, with its heterogeneous regional perfusion in the two anatomically and functionally distinct vascular beds of the renal cortex and medulla, and with its non-uniform blood vessel geometries, presents a unique challenge for measuring intrarenal blood flow distribution. Determining whole organ perfusion, on the other hand, is comparatively simple for the kidney, but it provides relatively little information about the suspected dependency of renal excretory function on local perfusion rate. Among the variety of methods proposed for gauging regional renal blood flow, some depend on measuring one or more of the tissue's thermal properties. The most straightforward, but least reliable, involve measurements either of focal tissue temperature alone, or of regional tissue thermal gradients. Simply using heat as a diffusible indicator, however, is unreliable as a measure of blood flow, for many of the same reasons that using an inert gas in a dilution technique is unreliable. Recently developed thermal analytical methods, though, hold promise for measuring local tissue blood flow with accuracy and precision. Two of them are reviewed here. One depends on measurement of the effective thermal conductivity of a small mass of tissue by evaluating the steady state ratio between regional unidirectional heat flux across it and the associated temperature gradient in one vector along a segment of it through an imposed spheroidal heat field. The other depends on analyses of tissue temperature decay subsequent to a controlled pulse of heat delivered through a small inserted thermistor bead. Both techniques use bioheat transfer equations to deduce regional blood flow by differentiating between heat dissipation due to local thermal conductivity and that attributable to the effects of regional convection. Although both methods are unavoidably invasive, neither produces debilitating damage in the tissue volume in which perfusion is measured, nor increases local temperature or metabolism enough to affect blood flow itself. Both techniques quantify local blood flow in small volumes of tissue by detailed evaluation of the many properties of tissue and blood which affect heat transfer, and both allow for a virtually unlimited number of nearly continuous sequential measurements at short (nom. 1 min) time intervals.

Objective, Real‐Time, Intraoperative Assessment of Renal Perfusion Using Infrared Imaging

“…However, we feel that the described method has many potential advantages over these technologies. Invasive methods or methods requiring direct contact with the parenchyma clearly cause tissue trauma or compression that affect local perfusion (27, unpublished observations). Additionally, most methods provide regional (ultrasound) or aggregate (thermo‐dilutional) information, but not both (28).…”

The Flow of Blood-Based Hybrid Nanofluids with Couple Stresses by the Convergent and Divergent Channel for the Applications of Drug Delivery

“…The temperature involvement in blood flow depends on the focal tissue temperature and thermal gradients. To sustain the uniform flow of blood and avoid the turbulence factor, researchers [25][26][27][28][29][30][31] used the temperature field in the blood flow analysis using various channels. The parameters involved in the energy equations vary in order to sustain the uniformity of blood flow in various circumstances and to improve the capability of drug delivery.…”

Assessment of renal graft function by perioperative monitoring of cortical microcirculation in kidney transplantation.1

“…In the past, available thermodiffusion devices were handicapped by specific limitations, particularly the necessity to induce a temporary "noflow" situation for preliminary measurement of the effective tissue conductivity (11,12). A new prototype device avoiding no-flow calibration proved to be a valid technique for continuous monitoring of renal and hepatic perfusion in a porcine model and has been transferred to the clinical setting for quantification of hepatic microcirculation after liver transplantation (13)(14)(15).…”