Fabrication of prototype for measuring the exhaled breath temperature (EBT) to support detection of asthma

Recently, EBT has been proven as the marker of airways inflammation like asthma and proposed as the non-invasive tool. Although EBT device has already been made but this device is rarely used for patients in Indonesia. The aim of this study is to develop a prototype which accurately measures EBT and is comfortably used by patients including children. This prototype was made using SHT11 as a sensor of EBT which is integrated on a thermal flask 0.5L. This flask filled up patient breath and the temperature of air breath was measured. The EBT of twelve healthy samples and seven samples with asthma was examined using this prototype, the measurement was done within three minutes for all of them. The test results of EBT on healthy samples obtained the median is 33.9°C within of 33.0°C - 34.7°C and EBT on asthma samples obtained median is 35.0°C within the range 34.9°C - 36.0°C.


Introduction
Health is one of the most important parts of life. The level of a person's health can be determined from several aspects, one of which is on the performance of a respirator. Asthma is a chronic disease which attacks the respiratory tract bronchial on our lungs, where there is inflammation bronchial cavity wall resulting in constriction of the airways that ultimately leads a person experience shortness of breath. Paredi et al, in their study found that patients with asthma had a rise in EBT that were faster than normal people [1]. Garcia et al, in their research also found the same thing regarding the relationship between EBT and asthma. The research found that healthy people EBT was 33.2 ± 0.2°C compared to patients with uncontrolled asthma that was 33.7 ± 0.8°C and patients with uncontrolled asthma that was 34.9 ± 0.8°C [2]. Popov et al shows that EBT can distinguish both samples with and without asthma. In their research, the obtained EBT asthmatics are in the range from 34.12 to 36.09 and from 32.29 to 35.84 °C for healthy people [3], [4], [5].
To fulfill the purposes of measurement of EBT, it needs to be made an instrument that is capable of measuring EBT precise and easy to use. This article discusses the prototype of the measuring instrument EBT using SHT11 sensor-based microcontroller ATmega16 as an instrument for supporting the treatment of asthma.

Materials and methods
Steps to prepare the prototype for measuring EBT to support detection of asthma can be shown in Figure 1. All steps of fabrication of the system were done in the Laboratory Instrumentation of Physics on Faculty of Mathematics and Natural Sciences, Universitas Lambung Mangkurat. Then, the step testing system to support asthma detection was done in Regional General Hospital Ulinon Banjarmasin, South Kalimantan.

Figure 1
The steps to prepare the prototype..

Preparation tools and materials
Tools and materials used were electronics equipment, multimeter, personal computer, power supply, microcontroller module minimum system ATMega16 [6], RTC module, the SHT11 sensor with i2c interface [7], thermal flask, RS232 module, LCD 16x2 module, BASCOM, Personal Computer and several of cables.

Design prototype of EBT
A design of the system can be shown in Figure 2. The figure shows that the EBT is collected on the thermal flask then the EBT is measured with the SHT11 sensor and the data of EBT are displayed by LCD and saved by a personal computer.

Fabrication module electronics and mechanics
The electronics part of prototype consists of sensor SHT11 placed in the thermal flask, module RTC (Real Time Clock), module LCD 2x16 and power supply. The power supply and RTC use the circuit that with microcontroller ATMega16 module. The interface of LCD 2x16 module with microcontroller module using configuration 4 bit. All the modules electronics are assembled and laid International on the box.Prototype electronic parts have the following specifications power supply with the output voltage of 5V, 12V and 12V. Power supply 5 V is required to turn SHT11 and minimum system. Minimum system ATmega16 uses 11.059200 MHz crystal. The form of mechanics module is just the modification of thermal flask used to keep warm the liquid in it. It is equipped with the mouthpiece to blow the air from breathing results.

Integration of electronics and mechanics module
The integration between the two modules uses a cable that connects the sensor module SHT11 with ATmega16 microcontroller i2c input. The connection of data from the electronics part of a prototype to a personal computer use the RS232, type of digital communication. It was selected to prevent lost data on the cable connected to them because of the length of a cable. The prototype has integrated shown in Figure 3.

Characterization of sensor SHT11
The characterization of SHT11 sensor aims to look at the performance of the sensor compared with a standard digital thermometergenerating a correction factor from the prototype to the exhaled breath temperature measured. Characterization is done by placing SHT11 and the thermometer in the same position in the thermal flask. The hot air is passed through a small tube into a thermal flask. Measurements were performed within a temperature range of 20 -60°C with a temperature recording every increase of 0.1°C. The result in Figure 5 (a) shows the differences of SHT11 and thermometer readings and calculation. It isobtained that the temperature correction value was 3.5°C. based on the average of the difference between the temperature value by digital thermometer with a temperature value measured by the prototype. This correction added values of SHT11 and the result has been shown in Figure 5 (b).

Figure 5 Characterization SHT11
On the results of correction as shown in Figure 5 (b) it was performed the paired t-test to determine whether the presence or absence of the difference in temperature readings by prototypes and digital thermometer. Based on the calculation, t value was -2.02 than from the t distribution table for df = 400 t for 99% confidence interval of 2.5882, the value of t<t distribution table so Ho is accepted. It means that there is no difference between a prototype and a digital thermometer.

Test of prototype
Tests were performed on 10 samples with repetition of data collection three times to determine the repeatibility of measurement. The test results are shown in Table 1.

Data analysis
The next test of a prototype was conducted on 12 healthy samples and samples of 7 people with asthma. The highest temperature measured was taken as the measured value of EBT. The test results in healthy samples are shown in Table 2 and the results of tests on healthy samples are shown in Table 3.  The value of EBT comparison charts of one sample of healthy and asthmatic is shown in Figure 6, starting at the second to 0-180s. Table 1 shows that the performance measurement repeatability deviation of EBT was in the range 0.115-1.415, meaning the prototype can measure EBT correctly on samples.  Figure 6 shows a graph EBT difference between normal samples and samples with asthma. EBT for the sample chart with asthma is increasing faster than the normal sample from 0 to 180 seconds. EBT value at 180 seconds is considered a sample value EBT that was recorded.

Result and Discussion
A thermal flask in this research was used withour the feature to clear the air after use, so they need a few minutes to equalize the initial conditions for the next EBT measurement.
The performance of the prototype needs to be improved to enhance EBT measurement and store data without using a personal computer, so that the necessary storage modules on the prototype so that data can be read by a computer for further analysis. Then it should also be used for the LCD graphic to display data EBT measured directly on the prototype.

Figure 6
The difference graphics between EBT asthma and normal

Conclusion
Based on the results and discussion we concluded that the prototype can measure samples EBT in healthy and asthmatic. Results of prototype testing on samples of healthy EBT values obtained ranges from 30.3 to 34.7°C and the sample asthmatics EBT values obtained ranges from 34.9 to 36.3°C.