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2.5. Respiration sensor
Respiration measurement often includes two classes: physiological parameter measurement
and gas ingredient from respiration system. What sensor the former utilizes is physical sensor,
and what sensor the latter employs is chemical sensor and biological sensor. Here, respiration
sensor which belongs to the first class is only introduced and explained. The measurement of
respiration system is important basis of clinic diagnosis, and it is necessary for patients in the
fields of surgery, baby and critically ill patient’s monitoring, sports medicine, and medical
research. The measurement of respiration system could be classified into three classes of
parameters: respiration frequency, respiration flow and lung respiration volume.
In biomedical research or clinic monitoring, respiration frequency of patient needs to be
sometimes detected to record the physiological status. Figure 9 illustrates a kind of sensor for
respiration frequency based on thermistor sensing principle. Thermistor is mounted to the
front-end of binder. When binder clamps the nares, airstreams from body flows through the
surface of thermistor. According to the change of thermistor value, the respiration frequency
would be measured.
Figure 9. Electromagnetic blood flow sensor
Biomedical Sensor, Device and Measurement Systems
http://dx.doi.org/10.5772/59941
191

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Figure 10. Thermistor sensor for respiration frequency (a)structure diagram, (b)measurement diagram
Of course, elastic strain instrument could be also utilized to detect the respiration frequency.
Its sensing principle is such: resistance wire is fixed to the surface of elastic plastic pipe. And
then mercury or other electrolyte is sealed into the elastic plastic pipe. After elastic plastic pipe
is adhered to the front of breast, respiration would lead to the length change of elastic plastic
pipe. Such length change causes the change of resistance wire which could show the change
of respiration frequency. When resistance wire is introduced into a detecting circuit, the
respiration frequency will be sensed and measured.