Respiratory rate detection by a time-based measurement system

  • E. Sifuentes Departamento de Ingeniería Eléctrica y Computación, Universidad Autónoma de Ciudad Juárez, Chihuahua-México
  • J. Cota-Ruiz Departamento de Ingeniería Eléctrica y Computación, Universidad Autónoma de Ciudad Juárez, Chihuahua-México
  • R. Gonzalez-Landaeta Departamento de Ingeniería Eléctrica y Computación, Universidad Autónoma de Ciudad Juárez, Chihuahua-México
Keywords: time-based measurements, Wheatstone bridge sensors, respiratory rate, temperature

Abstract

 

This paper proposes a system that converts a time-modulated signal from a resistive sensor into a digital signal with the goal to estimate the respiratory rate of a subject. To detect breathing, a known method based on a nasal thermistor, which detects temperature changes near the nostrils, is used. In this work, the thermistor mounted in a Wheatstone bridge, forms a RC circuit which is connected directly to a microcontroller, without using any analog circuit or analog-digital converter. Thus, whenever the subject breathes, it causes a fractional change in resistance x (Δ R/R0) on the thermistor, and this produces a time-modulated signal that is directly digitized with the microcontroller. Measurements were made on 23 volunteers, obtaining changes of x > 0.01. The temperature resolution was 0.2 °C, and the time response was 0.8 s, mainly limited by the thermistor properties; these features were enough to obtain a well-defined waveform of the breathing, from which was easy to estimate the respiratory rate by a compact, low cost and low power consumption system. Unlike interface circuits based on the voltage or current amplitude, with this kind of interface, the self-heating of the sensor is avoided since the thermistor does not require any voltage or bias current.

Published
2016-05-15
How to Cite
Sifuentes, E., Cota-Ruiz, J., & Gonzalez-Landaeta, R. (2016). Respiratory rate detection by a time-based measurement system. Mexican Journal of Biomedical Engineering, 37(2), 91-99. https://doi.org/10.17488/RMIB.37.2.3
Section
Research Articles