An isothermal flowmeter with improved frequency response for measuring tissue blood flow

Area of Science:

• Biomedical Engineering
• Physiological Measurement

Background:

• Accurate measurement of tissue blood flow is crucial for understanding physiological processes and diagnosing diseases.
• Existing methods for measuring tissue blood flow often face limitations in frequency response, probe size, or temperature sensitivity.

Purpose of the Study:

• To develop and characterize an isothermal flowmeter with enhanced frequency response for measuring tissue blood flow.
• To design a compact and simple probe utilizing thermistors for improved tissue blood flow measurement.

Main Methods:

• Developed an isothermal flowmeter using directly heated thermistors in small capillary probes (0.5 mm outer diameter).
• Employed a feedback current system to maintain thermistor temperature and a second thermistor for tissue temperature compensation.
• Evaluated the device's dynamic performance, including frequency response and linearity at different flow rates.

Main Results:

• The developed flowmeter demonstrated a low-pass frequency response with a cut-off frequency exceeding 5 Hz.
• The output signal was proportional to flow at low rates, with linearization required for higher flow rates.
• The device proved insensitive to tissue temperature, enabling continuous, long-term recordings and potential for in-vivo calibration.

Conclusions:

• The novel isothermal flowmeter offers a significant improvement in frequency response for tissue blood flow measurement.
• Its simple construction, small probe size, and temperature insensitivity make it suitable for various research and clinical applications.
• The device facilitates accurate and continuous monitoring of tissue perfusion.