Lecture 2 - mHealth and Sensor PDF

Lecture 2 - mHealth and Sensor Outline Heart Rate Monitoring Cardiac Conduction System ECG Measuring Device Holter Monitor Chest Strap Pulse PPG Technology PPG Measuring Device Smart watch (Apple watch) Smart ring mHealth (Mobile Health) The Global Observatory for eHealth of the World Health Organis...

Lecture 2 - mHealth and Sensor Outline Heart Rate Monitoring Cardiac Conduction System ECG Measuring Device Holter Monitor Chest Strap Pulse PPG Technology PPG Measuring Device Smart watch (Apple watch) Smart ring mHealth (Mobile Health) The Global Observatory for eHealth of the World Health Organisation (WHO) defines mHealth as: “medical and public health practice supported by mobile devices, such as mobile phones, patient monitoring devices, personal digital assistants and other wireless devices.” Heart Rate Monitoring Heart rate is affected by Health of cardiovascular system Lecture 2 - mHealth and Sensor 1 Levels of physical activities Mood Heart Rate Monitor A personal monitoring device to measure the heart rate in real time Areas of usage In hospital In sport activities Methods of recording heart signals Electrical: ECG sensors measure the electrical activity of the heart Optical: PPG sensors measure blood volume in the vessels The Heart Lecture 2 - mHealth and Sensor 2 Cardiac conduction system Electrical impulses control the contraction and relaxation of heart muscles (pump blood) Green structure is the nervous system within the heart Sinoatrial node has a pacemaker impulse in it to generate electrical signal ECG Electrodes on the skin pick up the heart’s electrical signals ECG (EKG) Heart rate: number of R waves per minute Atrium contracts pushes blood to the Ventricle Ventricle contracts pushing blood to the rest of the body Variations of ECG Devices Holter monitor (portable) Chest strap (wireless) Pros and cons of ECG measuring devices Pros: very accurate Cons: not convenient, may be uncomfortable Lecture 2 - mHealth and Sensor 3 Chest Strap (ECG) Smart Watch (PPG) Sensor Readings (Acquire Data) Storage (via Phone/Cloud) Data Processing (Algorithms) Display: Data Visualisation Pulse Every time your heart beats, it pumps blood through the arteries in your body As heart pushes out blood, in the arteries expand and artery pressure increases Between the beats, the arteries contract and artery pressure decreases Pulse rate = Heart rate Measure Pulse Feel the pulse (neck, elbow, wrist) Measure the change of blood volume (PPG) PPG (Photoplethysmography) Technology A LED light source shines green light onto the skin Green light is absorbed by the blood, more blood volume, more absorption of light Remaining green light bounces back into the photo detector Changes of light intensity picked up by the photo detector are proportional to the variations of blood volume Lecture 2 - mHealth and Sensor 4 Apple Watch (PPG) When your heart beats, the blood flow in your wrist is greater Between two heart beats, the blood flow is less Green LED light and photodetector (light-sensitive photodiodes) detect the amount of blood flor in your wrist at any given moment Signal processing algorithms are used to calculate the heart rate Comparing Green and Infrared Light PPG Sensors Green Light PPG Sensor Infrared Light PPG Sensor (Smart Watch) Great signal-to-noise ratio, resistance to motion artefacts Good signal-to-noise ratio but susceptible to motion artefacts, so need advanced and robust signal processing algorithms to filter out the noise (motion) Skin absorbs green light from the LED light source, which weakens the overall signal Tattoos, freckles and melanin in the skin do not affect reading accuracy Skin tone (amount of melanin) affects the skins ability to absorb green light which affects the reading accuracy Penetrate 10 times deeper into multiple tissue layers; obtain a number of biometric signals (such as hydration, muscle oxygen saturation, total hemoglobin and more) Hemoglobin strongly absorbs green light, so green light is unable to reach the deeper tissue to extract physiological insights Smart Ring Measure: heart rate, blood oxygen saturation Contains: optical sensor unit, RF transmitter and a battery, connected to a microcomputer inside the ring Can do low-level signal processing, data acquisition, filtering and bidirectional RF communication with a cellular phone which can access a website for data analysis and clinical diagnosis Lecture 2 - mHealth and Sensor 5 Light weight, comfortable to wear (even during sleep), low power consumption (charge once per week) Health tracker: heart rate, blood oxygen level, body temperature, sleep, activity Provide personalised recommendations based on user’s biometric data Help to detect early signs of some diseases PPG wave is susceptible to motion, if we move the ring the wave may change Solution: two ring sensors, one does not move, the other moves normally to produce a motion corrupted signal which has had motion noise removed. Another solution is to wear an accelerometer, which can measure the disturbances caused by motion Oura Ring App Sleep Score Total sleep time Sleep efficiency Resting heart rate Duration of each sleep stage Recommendation Above 85 means your sleep is optimal Between 74 and 84 means your sleep is good Under 70 means your sleep needs to be improved (Alcohol consumption affects sleep quality) Readiness Score Heart rate overnight Heart rate variability Body temperature Lecture 2 - mHealth and Sensor 6 Activity from previous day Sleep Recommendation Above 70 is good, indicating you are ready for the day Lower score indicates you need some rest if consistently getting a low score, it indicates you are not getting enough sleep or rest. Heart Rate Monitors Types of PPG-based monitoring devices Wristband-type (smart watch, smart band) Finger-type (ring sensor) Ear type (Earring sensor, earphone sensor) Forehead-type Pros and cons of PPG-based devices Pros: inexpensive, low power consumption, highly portable, very convenient to wear Cons: need to remove motion artefacts in PPG signals to get accurate readings Lecture 2 - mHealth and Sensor 7