Development of a Wearable Device for PHR Application

Ⅰ. Introduction

Advancement of modern medicine and improvement in standards of living have increased the average lifespan, and the number of elderly and chronic patients has risen sharply. The elderly and chronic patients are prone to diseases such as hypothermia, heatstroke, cardiac infarction, and digestive disorders owing to hypofunction in the sensing ability that detects a change in body temperature through malfunction of the autonomic nervous system.

Human body can be divided into the core and outer parts. Core temperature remains constant owing to the heat generated through basal metabolism of somatic cells. The outer part serves as an insulator between the core part and the external environment. The heat, generated in the core part through basal metabolism of somatic cells, is carried to the outer part through tissues and blood. The temperature of peripheral areas is kept constant through gain or loss of heat from external environments in the outer part. [1-3] In a healthy body, the core temperature is maintained at approximately 37–38 °C, with a temperature change of 0.5–1 ℃. When the body temperature increases or decreases beyond the said range owing to an abrupt temperature change, the body maintains the temperature through physiological adaptation and behavioral responses. [4]

When hypothermia occurs owing to a decrease in body temperature, the blood vessels in the peripheral tissues constrict, which decreases the blood flow into the peripheral areas and the oxygen supply to the tissues. It mostly occurs in the limbs, rather than in the trunci. [5] The decrease in blood flow degrades local sensing abilities and causes muscle weakness, making the skin cold and pale. When such a condition is maintained for hours without treatment, the body temperature drops below 34.4 °C, and the pulse, respiratory activity, and blood pressure drop to a life-threatening level. [6]

Sunstroke, which can occur during heavy exercises or activities in a high temperature environment, causes dizziness, headache, and nausea. In addition, bodily tissues can be destroyed owing to a high body temperature, and there is a risk of death when the physiological defense function is lost.

In this study, we developed a wearable device that can monitor the heartbeat, blood oxygen, and body temperature by being connected to a body heat keeper [7-9] using a thermoelement, which is employed in various industry sectors for monitoring of the wearer’s health data.

Ⅱ. Biometric Information Measurement

The main controller of the wearable device and body heat keeper transmits and receives data through XBee. The body heat keeper was designed to be turned on and off depending on the body temperature measured by the wearable device. In addition, we developed an application that presents the collected data. The collected data on heartbeat, blood oxygen, and body temperature were transmitted in real time from the main controller to the application using Bluetooth.

The main controller’s MCU was selected considering LCD communication, Zigbee, and Bluetooth communication. USART communication was used for data transmission and reception with LCD, Zigbee, and Bluetooth. For data transmission and reception with a temperature sensor, the 12C port was used.

Figure 1 presents the flow diagram of the biometric data. For measurement of data on a patient’s heartbeat and blood oxygen, a sensor (MAX30102, Maxim integrated, USA) was used. For the measurement of data on the patient’s body temperature, an infrared temperature sensor (MLX90614B, Melexis, Belgium) was used.

Fig. 1.

Flow Diagram of Biometric Data

Ⅲ. Wearable Device Design and Development

Figure 2 depicts the wearable device’s MCU. It was a STM32F070 MCU, which is equipped with a 32-bit cortex M-0 processor, with a flash memory of 32-128 kB and SRM of 6-16 kB. Figure 3 presents the developed wearable device’s PCB. We connected the infrared temperature sensor and heartbeat and blood oxygen sensor in parallel for simultaneous sensing and used 12C communication to transmit and receive data.

Fig. 2.

Circuit Diagram of the Wearable Device’s MCU

Fig. 3.

Wearable Device’s PCB (a)Front, (b)Back

Figure 4 illustrates the circuit diagram of the infrared temperature sensor that was used for real-time contactless body temperature measurement. It is a small sensor that can measure an object’s surface temperature from –70 to +380 °C, with an error of ±0.5 °C and measurement resolution of 0.02 °C. We placed a pull-up resistor on the SCL and SDA pins to improve the accuracy and reliability of 12C communication. The real-time data on body temperature were configured to be transmitted to the main controller using 12C communication.

Fig. 4.

Circuit Diagram of the Infrared Temperature Sensor

Figure 5 presents the circuit diagram of the heartbeat and blood oxygen sensor. The characteristics of the sensor are provided in Table 1. The sensor shoots red light and infrared light from the LED and senses the reflection of the lights from the skin to measure the heartbeat and blood oxygen under the skin.

Fig. 5.

Characteristics of the Hearbeat and Blood Oxygen Sensor

Table 1.

Characteristics of the Hearbeat and Blood Oxygen Sensor

Ⅳ. Experimentation and discussion

The speed of data transfer between the wearable device and the controller was measured. The block diagram for the measurement of data transfer speed is provided in Figure 6, along with the measured value. We connected oscilloscope CH1 to the data transmitting end (TXD) of the sensor board and oscilloscope CH2 to the main controller. Then, we put the “GND” of the sensor board and oscilloscope to “COM ON.” The sensor board transmits data to the main controller. The main controller sets the output pin to high every time it receives data. The data transfer speed from the wearable device to the controller was measured to be 24.0

Fig. 6.

(a)Block Diagram for Response Speed Measured Data

To calculate the impact of body heat maintenance on the biometric data, we put on the wearable device and measured the biometric data before and after wearing the body heat keeper.

First, we measured the data at 5 min intervals when we stopped, walked, ran, walked, and stopped in the written order while wearing the wearable device only. Subsequently, we put on the body heat keeper, along with the wearable device, and measured the data at 5 min intervals when we stopped, walked, ran, walked, and stopped in the written order.

Figure 7 depicts the changes in heartbeat before and after wearing the body heat keeper. The changes before wearing it are provided in (a), whereas the changes after wearing it are provided in (b).

Fig. 7.

Changes in Hearbeat Based on Wearing the Body Heat Keeper

The average heartbeat before wearing the body heat keeper when stopped was 81.9 bpm, whereas the average heartbeat after wearing it was 81.6 bpm. The average heartbeat before wearing the body heat keeper after walking and running was 83.7 bpm, whereas the average heartbeat after wearing it was 83.4 bpm. The average heartbeat before wearing the body heat keeper after walking and stopping was 82.6 bpm, whereas the average heartbeat after wearing it was 82.2 bpm. These results demonstrated that the heartbeat was stabilized slightly more quickly after wearing the body heat keeper than before wearing it.

Figure 8 presents the changes in body temperature before and after wearing the body heat keeper. The changes before wearing it are provided in (a), whereas the changes after wearing it are provided in (b).

Fig. 8.

Changes in Body Temperature Based on Wearing the Body Heat Keeper

The result of comparison of the body temperature changes revealed that the average body temperature was lower by 0.1 ℃ after wearing the body heat keeper than before wearing it when the wearer ran, thereby demonstrating that, after walking and stopping, the body temperature was recovered to the normal level in a more stable manner after wearing the body heat keeper.

Figure 9 depicts the changes in blood oxygen before and after wearing the body heat keeper. The changes before wearing it are provided in (a), whereas the change after wearing it are provided in (b). The average blood oxygen was 99.5 bpm. Therefore, there was no significant change in blood oxygen owing to the use of the body heat keeper, similar to the heartbeat and body temperature.

Fig. 9.

Changes in Blood Oxygen Based on Wearing the Body Heat Keeper

Ⅴ. Conclusion

In this study, we developed a wearable device for PHR application and measured real-time changes in the device wearer’s heartbeat, blood oxygen, and body temperature. The results of the measurement of the changes in heartbeat, blood oxygen, and body temperature using the wearable device revealed that the data transfer speed appeared to be as fast as 24.0 ms. There was no significant change in heartbeat, blood oxygen, and body temperature owing to the use of the body heat keeper in the experiment wherein the measurement was performed when the wearer stopped, walked, ran, walked, and stopped, presumably because the experiment participant was a healthy normal person. It is expected that the device will produce basic data for health management of the elderly and chronic patients if it is worn by them on a daily basis. In particular, if the biometric data collected by the wearable device are linked with hospital data, it will be possible to collect and manage high-quality personal health information for improvement of the wearer’s health.

Acknowledgments

This paper is that revised and supplemented the research results supported by the Small and Medium Business Promotion Agency (S2759360) in 2019.

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