Biomedical Instrumentation

Biomedical Instrumentation
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Published Date:21-07-2017
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Biomedical Instrumentation A. Intro & ECG B18/BME2 Dr Gari Clifford (Based on slides from Prof. Lionel Tarassenko) Biomedical Instrumentation B18/BME2 Who am I?  UL in Biomed Eng  Dir CDT in Healthcare Innovation IBME  Signal Processing & Machine Learning for Clinical Diagnostics  mHealth for Developing Countries  Low Cost Electronics  EWH / OxCAHT Biomedical Instrumentation B18/BME2 Vital signs monitoring Clinical need  Every day, people die unnecessarily in hospitals  20,000 unscheduled admissions to Intensive Care p.a.  23,000 avoidable in-hospital cardiac arrests per annum  Between 5% and 24% of patients with an unexpected cardiac arrest survive to discharge  Vital sign abnormalities observed up to 8 hours beforehand in 50% of cases Biomedical Instrumentation B18/BME2 Identifying at-risk patients  Acutely ill patients in hospital (e.g. in the Emergency Dept) have their vital signs (heart rate, breathing rate, oxygen levels, temperature, blood pressure) continuously monitored but…  Patient monitors generate very high numbers of false alerts (e.g. 86-95% of alarms - MIT studies in ‘97 & ‘06)  Nursing staff mostly ignore alarms from monitors (“alarm noise”), apart from the apnoea alarm, and tend to focus instead on checking the vital signs at the time of the 4-hourly observations Biomedical Instrumentation B18/BME2 Continuous bedside monitoring in Emergency Department Biomedical Instrumentation B18/BME2 Course Overview 1. The Electrocardiogram (ECG) 2. The Electroencephalogram (EEG) 3. Respiration measurement using Electrical Impedance Plethysmography/Pneumography 4. Oxygen Saturation using Pulse Oximetry 5. Non-invasive Blood Pressure Biomedical Instrumentation B18/BME2 Course text books  Biomedical Engineering Handbook, Volume I, nd 2 Edition, by Joseph D. Bronzino (Editor), December 1999, ISBN: 0-849-30461-X  Medical Instrumentation: Application and Design, 3rd Edition, by John G. Webster (Editor), December 1997, ISBN: 0-471-15368-0 Biomedical Instrumentation B18/BME2 Relevant lecture notes  OP-AMP CIRCUITS – Year 1, pages 1 to 42  FILTER CIRCUITS – Year 1, pages 1 to 15  INSTRUMENTATION – Year 2, pages 1 to 4, 17-18, 22 to 28 and 38 to 52.  Please e-mail if you would like copies of the above.  Course website: Biomedical Instrumentation B18/BME2 Quick Vote  Do you want all these lectures printed out each day? (You can use laptops etc to take notes, just don’t check your email.) Biomedical Instrumentation B18/BME2 ToDo (for you)  Sign up on weblearn for revision sessions (15 max per session)  B18 (Undergrad)  Question sheet 1: three sessions, 9 a.m. - noon on Friday of Week 7, in LR4  Question sheet 2: three sessions 9 a.m. - noon on Friday of Week 8, in LR4  MSc:  Question sheet 1: a single session for all students, 3 - 5 p.m. on Friday of Week 7, in LR3  Question sheet 2: a single session for all students, 3 - 5 p.m. on Friday of Week 8, in LR3 Hand in sheets before hand Biomedical Instrumentation B18/BME2 Biomedical Instrumentation 1. The Electrocardiogram (ECG) Biomedical Instrumentation B18/BME2 The Electrocardiogram  If two surface electrodes are attached to the upper body (thorax), the following electrical signal will be observed:  This is the electrocardiogram or ECG Biomedical Instrumentation B18/BME2 The origin of the ECG  Atrial and ventricular contractions are the result of carefully timed depolarisations of the cardiac muscle cells • The timing of the heart cycle depends on:  Stimulus from the pacemaker cells  Propagation between muscle cells  Non-excitable cells  Specialised conducting cells (Atrio-Ventricular Node) Biomedical Instrumentation B18/BME2 Important specific structures  Sino-atrial node = pacemaker (usually)  Atria  After electrical excitation: contraction  Atrioventricular node (a tactical pause)  Ventricular conducting fibers (freeways)  Ventricular myocardium (surface roads)  After electrical excitation: contraction Biomedical Instrumentation B18/BME2 Excitation of the Heart Biomedical Instrumentation B18/BME2 Excitation of the Heart Biomedical Instrumentation B18/BME2 Cardiac Electrical Activity  Putting it al together: Biomedical Instrumentation B18/BME2 Approximate model of ECG  To a first approximation, the heart can be considered to be an electrical generator.  This generator drives (ionic) currents into the upper body (the thorax) which can be considered to be a passive, resistive medium  Different potentials will be measured at different points on the surface of the body Biomedical Instrumentation B18/BME2 Recording the ECG P1 R T1 P1 RA LA P2 R P R T2 P2 RL LL Points P1 and P2 are arbitrary observation points on the torso; R is the resistance between them, and R , R are lumped P T1 T2 thoracic medium resistances. . Biomedical Instrumentation B18/BME2 Typical ECG signal Biomedical Instrumentation B18/BME2