25-02-2013, 12:44 PM
A Portable Respiratory Rate Recorder for Athletes
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ABSTRACT
This report describes the development of a portable respiratory rate recorder
(PRRR) for athletes. Respiratory rate is an important parameter, because it can be
used to detect the anaerobic threshold.
The PRRR can be used to measure the respiratory rate of athletes during exercise
in the field, whereas existing devices can only be used in a laboratory. The
measured respiratory rate is shown on a liquid crystal display and stored in
memory. When the measurement is completed, the PRRR can be connected to a
personal computer, to load the results for further analysis.
The first step in the project was the formulation of the requirements for such a
device. Also the user interface was specified. During the project a new sensor for
measuring the respiratory signal of an athlete was developed. This consists of a
pressure sensor mounted in a flexible belt around the chest of the athlete.
The hardware of the PRRR consists of a Philips microcontroller with a built-in AiD
converter with some supplementary circuits. A custom active filter/amplifier has
been designed to convert the signal from the sensor into a signal which is suitable
for the AiD converter. An earlier developed frequency analysis method is used to
determine the respiratory rate from the measured signal. This function and the other
software is written in the 'e' language.
INTRODUCTION
General introduction
The Master Programme Information Technology (ITW) at the Eindhoven University
of Technology (TUE) is completed with a nine-month graduation project.
This report describes the results of my graduation project at the group of Medical
Electrical Engineering of the Department of Measurement and Control Systems of
the Faculty of Electrical Engineering. The project consists of the design, realisation
and evaluation of a Portable Respiratory Rate Recorder for athletes (PRRR).
Respiratory rate and exercise
A Portable Respiratory Rate Recorder for Athletes
As you will know from your own experience, the respiratory rate increases as one
exercises. This is an example of the phenomena that are studied in the field of
exercise physiology. Professor H. Kuipers of the Group of Movement Sciences of
the University of Limburg (RL) studies the variability of physiological responses to
exercise. This chapter gives a brief overview of some results of this study.
Interested readers can find more in Kuipers[1983] and Cheng[1992].
The "fuel" the human muscle needs, is an energy-rich phosphate called ATP. This
ATP can be generated in two ways. The first way consists of the breakdown of
glucose with the use of oxygen in the blood. The uptake of oxygen by the lungs is
limited. When the maximum is reached and still more power is needed, the second
way to produce ATP is activated. This so called anaerobic metabolism consists of
the breakdown of glucose to lactic acid (lactate).
The anaerobic energy delivery can only be used for a few minutes because it
causes the intracellular pH to drop. In this situation the function of the muscle
decreases and the desired power can no longer be produced.
Frequency analysis of the respiratory signal
The Portable Respiratory Rate Recorder (PRRR) has to determine the respiratory
rate, in other words the frequency of the measured signal. In an earlier stage of this
project different frequency analysis methods were developed and tested. One of the
methods was the implementation of the Fast Fourier Transform (FFT). A drawback
of this implementation is that the results are not reliable. Further it uses a lot of
arithmetic operations.
The most effective method proved to be a variant of the Orthogonal Search Method
(OSM). In this section we will take a closer look at it. More about the OSM method
and the E-function in (3.2) can be found in Phoelich[1994].