HEALTH STATE MONITORING SYSTEM DESIGN A Project Presented to the faculty of the Department of Electrical and Electronic Engineering California State University, Sacramento Submitted in partial satisfaction of the requirements for the degree of MASTER OF SCIENCE in Electrical and Electronic Engineering by Viorel Rotar FALL 2012 HEALTH STATE MONITORING SYSTEM DESIGN A Project by Viorel Rotar Approved by: __________________________________, Committee Chair Dr. Warren D. Smith __________________________________, Second Reader Koullis Pitsillides ____________________________ Date ii Student: Viorel Rotar I certify that this student has met the requirements for format contained in the University format manual, and that this Project is suitable for shelving in the Library and credit is to be awarded for the Project. __________________________, Graduate Coordinator, __________________ Preetham B. Kumar Date Department of Electrical and Electronic Engineering iii Abstract of HEALTH STATE MONITORING SYSTEM DESIGN by Viorel Rotar The health of hospitalized patients often deteriorates, because the available medical staff is unaware of the deterioration. The condition of normally healthy people under stressful situations can deteriorate, because they are not aware that they have reached their physical limits. Infants can die in their “Sleep” because of Sudden Infant Death Syndrome (SIDS). Death could be prevented by waking the child, but the parents are unaware that the infant experiences lack of oxygen. People with epilepsy can die because a seizure was not detected in a timely manner. In severe epileptic episodes, death from airway constriction can occur in less than 3-5 minutes unless help is immediately provided. Therefore, a Health State Monitoring System (HSMS), able to detect and alarm when a health abnormality develops, is desirable. The HSMS should be broadly useful from being used by professional health-care providers to personal in home use. It should be easy to use by first responders, military personnel, firefighters, athletes, and parents monitoring infants. iv The HSMS consists of a wearable device with sensor and communication circuitry, a personal computer (PC) based graphical user interface (GUI), and a base- station interface between the wireless sensor and the PC. The wearable device incorporates sensors that can provide a quick general assessment of a person’s cardio- respiratory status, temperature, and level of physical activity. The cardio-respiratory status is assessed by a pulse oximeter, which gives the percent oxygen saturation in the blood. Heart rate is derived from the pulsatile waveform of the pulse oximeter which corresponds to the cardiac cycle. Skin temperature is measured with a digital temperature sensor. A micro Secure Digital (microSD) card is used to store raw data for extended periods of time. The sensors for vital data acquisition are non-invasive and do not require a professional health care provider for attachment to the body. The system is configurable to accommodate different applications. For continuous patient monitoring, the system can be configured to wirelessly transmit collected data to a computer. These data then can be sent to a physician, who then reviews the data and intervenes when necessary. For applications where a computer is out of wireless communications range, like when monitoring the effect of stressful situation on health of first responders, the data are saved on the microSD card for later review. For applications where just an alarm is necessary to indicate a breathing or heart rate abnormality, such as monitoring of infants for the detection of SIDS, for example, the system can be configured to activate the light and/or sound alarm. v In this project, a small wearable wireless sensor was designed and built that incorporates multiple sensors, and all the sensors operated properly in a laboratory setting. The sensors that are less susceptible to motion artifacts, such as temperature, were easier to implement. The pulse oximeter performed well under different light conditions, but data were disrupted or incorrect as a result of motion artifacts. Development of software algorithms to reduce the effects of motion artifacts is desirable. The pulse oximeter signal was obtained easily when a finger was placed over the sensor, but the sensor was not tested at other locations on the body. The wireless communication was stable, with a range suitable for hospital and home use. The necessity for different component values for the transceiver, if there is a need to change the frequency band to comply with local radio-communication rules, is a drawback. Approved by: __________________________________, Committee Chair Dr. Warren D. Smith ____________________________ Date vi ACKNOWLEDGEMENTS It is a pleasure to acknowledge the assistance received during the development of the Health State Monitoring System from Dr. Warren D. Smith, who is committee chair for the project, and Koullis Pitsillides, a biomedical engineer from Endosomatic Systems. vii TABLE OF CONTENTS Page Acknowledgements ........................................................................................................... vii List of Figures .................................................................................................................... xi Chapter 1. INTRODUCTION ........................................................................................................1 2. BACKGROUND ..........................................................................................................5 2.1. Temperature Monitoring ....................................................................................5 2.1.1. Temperature Monitoring Importance ................................................. 5 2.1.2. Temperature Measurement Principle ................................................. 6 2.2. Activity Monitoring ...........................................................................................8 2.2.1. Activity Measurement Importance ..................................................... 8 2.2.2. Activity Measurement Principle ......................................................... 9 2.3. Cardio-Respiratory Assessment .......................................................................10 2.3.1. Pulse Oximeter Importance .............................................................. 10 2.3.2. Principle of Pulse Oximeter Measurements ..................................... 11 2.3.3. Optical Properties of the Tissue ....................................................... 12 2.3.4. Transmission and Reflectance Modes of Pulse Oximeter Measurements .................................................................................. 18 2.3.5. Interference to the Pulse Oximeter Signal ........................................ 19 3. HEALTH STATE MONITOR CIRCUITRY ............................................................21 viii 3.1. Health State Monitor Circuitry Overview........................................................21 3.2. Sensor Circuitry ...............................................................................................23 3.2.1. Temperature Monitoring Circuitry ................................................... 24 3.2.2. Activity Monitoring Circuitry .......................................................... 25 3.2.3. Pulse Oximeter Circuitry .................................................................. 26 3.3. Supporting Circuitry ........................................................................................31 3.3.1. Power Supply Circuitry .................................................................... 31 3.3.2. Microcontroller (MCU) Circuitry ..................................................... 32 3.3.3. Radio Communication Circuitry ...................................................... 35 3.3.4. MicroSD Card Circuitry ................................................................... 36 3.3.5. Alarm Circuitry ................................................................................ 37 3.4. Base-Station Circuitry ......................................................................................38 4. WIRELESS SENSOR SOFTWARE ..........................................................................39 4.1. Microcontroller Main Routine .........................................................................39 4.2. Temperature Acquisition .................................................................................42 4.3. Accelerometer Acquisition ..............................................................................43 4.4. Pulse Oximeter Acquisition .............................................................................44 4.4.1. Pulse Oximeter Software Overview ................................................. 44 4.4.2. Controlling the LEDs and Taking Data Samples ............................. 46 4.4.3. Red and Infrared (IR) Signal Processing .......................................... 49 4.4.4. Calculating the Heartbeats ................................................................ 52 ix 4.4.5. Calculating the Percent Oxygen Saturation in Blood ....................... 55 4.1. MicroSD Card Software ..................................................................................58 4.2. Wireless Communication .................................................................................61 5. GRAPHICAL USER INTERFACE (GUI) ................................................................63 5.1. Initializing a Wireless