Abstract
Abstract Venous blood circulation can be restricted due to various conditions commonly indicating a related medical condition. However, current non-invasive methods for determining venous blood flow are limited to be either very inaccurate or expensive. Alternatively, a method to measure sap flow non-invasively in trees is through thermal mass measurement principles. This paper investigates applying the thermal mass flow measurement principle to determine venous blood flow. A simplified finite element model (FEM) and simulation are created to determine the operating behavior and expected response of a thermal mass flow meter with venous blood flow under the skin. An initial prototype of a thermal mass venous blood flow meter is designed using a Peltier-element and RTD thermistors. Initial tests were done on N = 8 subjects identifying the presence of blood flow and, testing the devices basic functionality and performance. The simplified FEM model of venous blood flow proved the thermal mass blood flow device is feasible, and determined the initial characteristics of the first prototype. The initial prototype proved to be functional detecting rises in temperature downstream of +1.4 K (0.8 - 1.8 inter- quartile range) when the blood flow was released (t = 90 s after release), compared to when blood was not flowing. The initial prototype proved to be able to detect the presence of blood flow in all subjects. However, further work is required to increase the differences in temperature values or gradient measured for a change in flow rate so the actual flow rate can be determined.
Highlights
The circulatory system is fundamental to the body’s functionality transporting necessary nutrients and oxygen to cells within organs and peripheral limbs
This paper investigates creating a venous blood flow measurement device using principles of thermal mass measurement similar to those seen in thermo-dilution and sap measurements
A large change in temperature (0.9 - 0.95 K) is seen when comparing to the no flow case, only very small differences (
Summary
The circulatory system is fundamental to the body’s functionality transporting necessary nutrients and oxygen to cells within organs and peripheral limbs. Changes in venous flow can indicate shock [1], dehydration [2], vein thromboses [3], and a general decrease in peripheral perfusion [4]. Restricting blood flow to peripheral limbs has been shown to induce muscle hypertrophy and increase strength gain with low intensity resistance training (KAATSU training) [5]. Vascular Doppler ultrasound is the most common technique for determining venous blood flow. The Doppler ultrasound is currently expensive, depends heavily on probe orientation and requires the assumption of vessel cross sectional area and average velocity to determine the mass flow rate. Other techniques such as the capillary nail re-fill test only give limited information about the venous flow rate
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