Research

In vitro calibration of a system for measurement of in vivo convective heat transfer coefficient in animals

Chanchana Tangwongsan^1* , Louay Chachati^2* , John G Webster^3* and Patrick V Farrell^4*

¹  Department of Electrical Engineering, Chulalongkorn University Phaya-Thai Road, Bangkok 10330, Thailand

²  Department of Electrical and Electronic Engineering, University of Aleppo, Aleppo, Syria

³  Department of Biomedical Engineering, University of Wisconsin, 1550 Engineering Drive, Madison, WI 53706, USA

⁴  Department of Mechanical Engineering, University of Wisconsin, Madison, WI 53706, USA

author email corresponding author email* Contributed equally

BioMedical Engineering OnLine 2006, 5:57doi:10.1186/1475-925X-5-57

Published:	26 October 2006

Abstract

Background

We need a sensor to measure the convective heat transfer coefficient during ablation of the heart or liver.

Methods

We built a minimally invasive instrument to measure the in vivo convective heat transfer coefficient, h in animals, using a Wheatstone-bridge circuit, similar to a hot-wire anemometer circuit. One arm is connected to a steerable catheter sensor whose tip is a 1.9 mm × 3.2 mm thin film resistive temperature detector (RTD) sensor. We used a circulation system to simulate different flow rates at 39°C for in vitro experiments using distilled water, tap water and saline. We heated the sensor approximately 5°C above the fluid temperature. We measured the power consumed by the sensor and the resistance of the sensor during the experiments and analyzed these data to determine the value of the convective heat transfer coefficient at various flow rates.

Results

From 0 to 5 L/min, experimental values of h in W/(m²·K) were for distilled water 5100 to 13000, for tap water 5500 to 12300, and for saline 5400 to 13600. Theoretical values were 1900 to 10700.

Conclusion

We believe this system is the smallest, most accurate method of minimally invasive measurement of in vivo h in animals and provides the least disturbance of flow.