BIOPOTENTIAL MEASUREMENT-ECG, EEG, EMG, PCG

BIOPOTENTIAL MEASUREMENT

1. UNIT II BIOPOTENTIAL MEASUREMENT

2. UNIT II BIOPOTENTIAL MEASUREMENT Bio signal characteristics– frequency and amplitude ranges. ECG – Einthoven‘s triangle, standard 12 lead system, block diagram. Measurements of heart sounds - PCG. EEG – 10-20 electrode system, unipolar, bipolar and average mode, EMG – unipolar and bipolar mode-Nerve conduction velocity

3. Electrocardiogram-ECG - biopotential generated by the muscles( myocardium ) of the heart during cardiac cycle ANATOMY OF HEART -

4. Heart has 4 chambers 1. left and right atria 2. left and right ventricle SA node(pacemaker) - group of cells spontaneously generate action potential at a regular rate -Action potential propagate in all direction -wave terminate at the center of heart (Atrioventricular(AV) -AV node contain delay line fibers that provide timing between the action of atria and ventricle -Once excitation passed through the delay line fiber, spread rapidly to all parts of the ventricle by bundle of His -Purkinje fiber-initiate action potential in ventricle https://www.youtube.com/watch?v=5tUWOF6wEnk

5. Pulmonary circulation - circulatory path for blood through the lung Systemic circulation -circular system that supplies oxygen and nutrients to the cells heart pumping cycle- systole and diastole Systole - period of contraction Diastole- period of dialation (expansion) Average heart rate-70beats/miniute(60 -100)- normal- R wave is positive slower rate(bradycordia) Higher rate (Tachycardia)

6. ECG leads Electrocardiograph - instrument to record cardiogram - 5 electrodes fixed to the body - colour code to identify the lead -4 electrodes , one reference(RL)

7. Types Bipolar limb lead- 3 lead Augmented Unipolar limb lead- 3 lead Unipolar chest lead- 6 lead ECG measurement-12 leads system(3+3+6) https://bmi-iitr.vlabs.ac.in/List%20of%20experiments.html

8. 1.Biploar limb lead(standard lead system) -For each lead, ECG is recorded from two electrode . Third electrode is not connected Three leads (right leg reference) 1. Lead I –voltage drop from Left Arm(LA) and Right Arm(RA) 2. Lead II - voltage drop from Left Leg(LL) and Right Arm(RA) 3. Lead III -voltage drop from Left Leg(LL) and Left Arm(LA)

9. V II =V I +V III Lead I Lead II Lead III Voltage V I V II V III P wave amplitude 0.53mV 0.71mV 0.38mV Duration 0.07-1.13 0.07-1.13 0.07-1.13

10. Einthoven triangle -Working of ECG lead system is defined by Einthoven - The closed loop from RA to LA, LA to LL, then LL to RA forming a triangle called Einthoven triangle - Sides of the triangle represent the line along which three projection of ECG waveform is measured - Voltage measured from any one of the three limb lead is equal to algebraic sum of other two - In Lead II , R wave amplitude is high = sum of R wave amplitude in lead I and lead II

11. 2. Augmented unipolar limb lead - record electrical activity from one lead - ECG recorded between single exploratory electrode and central terminal - central terminal is obtained by connecting two limb electrode together through equal resistance -potential at connection point =average potential other two electrode -The limb electrode used as a exploratory electrode is not used for central electrode . Therefore ECG amplitude increases Three leads 1. aVR (augmented Voltage Right arm) 2. aVL (augmented Voltage Left arm) 2. aVF (augmented Voltage Foot(left))

12. Augmented unipolar limb lead

13. 3. Unipolar chest lead - single chest electrode placed on six predefined points in chest in horizontal plane - Chest positions are called precordial unipolar leads -six leads V 1 to V 6 -All three limb electrodes used to obtain the central terminal , chest electrode is the exploratory electrode

14. V1 to V6 unipolar horizontal plane front to back

15. V 1 to V 6 waveforms

16. ALL 12 leads Frontal Plane Horizontal Plane

17. ECG RECORDER

18. Lead selector Switch - consists of resistor network and standardization volt(1mv) for calibration of recorder - amp. is switched off momentarily to avoid artifacts caused by the changes in the switch lead selector switch Pre amplifier - is the Differential amplifier with high CMRR -amplify the low amplitude ECG signal - AC coupled to avoid problems with DC vot. generated due to the polarization of electrode - Gain of the amplifier is adjusted by gain switch Pen amplifier (DC amplifier) -provide power to drive the pen motor (record ECG) -- pen motor control the position of pen on the recording paper – paper is coated with heat sensitive material like wax - pen is an electrically heated stylus (temp. of stylus is adjusted with stylus heat control) - marker stylus records the lead name at the margin of the paper

19. - Normal Paper speed is 25mm/s -50mm/s is allowed for better resolution of QRS complex Power switch - has three positions -ON-power to amp. turn on , paper drive is not running RUN – start recording Buffer amplifier - High input impedance amplifier -Present in each patient lead to provide over voltage protection

20. Electroencephalogram(EEG) -Bio electric potential generated by the activity of the brain - electrodes are placed at the surface of the scalp - waveform varies with the location of electrodes on the scalp and activity of the person - Frequency 1 to 100 Hz amplitude-10 microvolt to 100 microvolt Electrode used- surface, needle Brain wave –electrical activity of brain

21. EEG

22. STRUCTURE OF BRAIN Human brain contain12 billion neurons Four lobes Frontal lobe -primary motor action-leads to various muscles of the body Occipital lobe-back of the head over the cerebellum -contain visual cortex 3. Temporal lobe-Auditory sensory inputs are traced -neurons respond to sound 4. Parietal lobe - sensory inputs cerebellum - acts as microcomputer intercept sensory and motor nerves -maintain balance

23. EEG waves Delta - Theta Alpha Beta

24. Wave voltage Frequency Condition Region Delta Above 50 microvolt Below 3 .5Hz Deep and dreamless sleep Normally in babies Body is healing or resetting Theta Above 50 microvolt 3.5 to 8 Hz Light sleep , extreme relaxation Normally in young children Drowsy adult, emotional distress Occipital Alpha 50 to 100 microvolt 8 Hz to 13Hz Adult, Relaxed with eyes closed, get up in the morning 8 Hz in children Occipital Beta 20 microvolt Above 13 Hz to 38Hz Alert, wide awake and thinking, mental activity Common form of brain wave frontal region

25. -Natural ideal frequency of brain-alpha wave evoked response -measure of the disturbance in the EEG pattern results from external stimuli, such as a flash of light or a click of sound. Gamma waves -36 to 44Hz -Amp: 3.5micro volt -occur with sudden sensory stimuli

26. EEG Electrode System Each electrode site is labeled with a letter and a number . The letter refers to the area of brain underlying the electrode numbers refers to the right or left side of the head Region F - Frontal P - Parietal T - Temporal O - Occipital C – Central Numbering Odd – left Even –right Z-middle

27. 10 20 20

28. scalp electrodes are indicated. Further there are nasopharyngeal electrodes n1;and n2 and ear electrodes A1 and A2 . Draw two lines on the skull 1. from the nasion (root of the nose), to the inion ( ossification center). 2. from the left pre auricular (ear) point to the right pre auricular point . - intersection of these two lines is the mid point ( Cz ) Mark points at 10,20, 20,20 and 10% of the total nasion - inion distance . These points are Fpz , Fz , Cz,Pz and Oz . Mark points at 10, 20, 20, 20, 20 and 10% of the total distance between the preauricular points. These points are T3, C3, Cz , C4 and T4 . In these odd numbered points T3 and C3 are on the left and even numbered points C4 and T4 are on the right.

29. Measure the distance between Fpz and Oz along the great circle passing through T3 and mark points at 10, 20, 20, 20, 20 and 10% of this distance. These are the positions of Fp1, F7, T3, T5 and O1 . Repeat this procedure on the right side and mark the positions of Fp2, F8, T4, T6 and O2 . Measure the distance between Fp1and O1 along the great circle passing through C3 and mark points at 25% intervals. These points give the positions of F3, C3 and p3 The ground reference electrode is a metal clip on the earlobe. Repeat this procedure on the right side and mark the positions of F4, C4 and P4

30. F7, F3, Fz, F4 and F8 are equidistant along the transverse circle passing through F7, Fz and F8 T5, P3, Pz, P4 and T6 are equidistant along the transverse circle passing through T5, Pz and T6.

31. EEG recording Three types of recording Bipolar – – Measurement is between two electrodes spaced close together Unipolar – Measurement is between one electrode(active) and the indifferent electrode(reference- at ear lobe) Average reference mode- Activity from all the electrodes is measured, summed together and averaged before being passed through a high value resistor which is the reference

32. Each amplifier records the difference between a scalp electrode and a reference electrode. The same reference electrode is used for all channels. Electrodes frequently used as the reference electrode are A1, A2, the ear electrodes, or A1 and A2 linked together Unipolar recording mode

33. Bipolar- potential difference between a pair of electrodes is measured Bipolar recording mode These sequentially link electrodes together usually in straight lines from the front to the back of the head or transversely across the head. For example, the first amplifier may have electrodes FP1 and F3 connected to it and the second amplifier F3 and C3 connected to it .

34. Average reference recording mode Activity from all the electrodes is measured, summed together and averaged before being passed through a high value resistor. The resulting signal is then used as a reference electrode and connected to input 2 of each amplifier and is essentially inactive. All EEG systems will allow the user to choose which electrodes are to be included in this calculation

35. Lead selector - permit any two electrode to be connected to be connected to any channel of the instrument - Calibration signal is to be applied to any desired channel for calibration of the equipment Pre ampilfier : amplify the low voltage(1mv) EEG signal from several regions of the brain -high quality differential amplifier with high CMRR - High input impedence (>10Mhz)-to reduce the effect of change in electrode resistance, loading effect cut off frequency-1Hz B.W -50-100Hz Power amplifier : - drive pen of each channel for recording -may be a dc amplifier to reduce the variation in dc electrode potential Band rejection filter - frequency-60Hz -To reduce the power line interference Filter bank : EEG signal is separated into different bands (LP, BP,HP ) for analysis Display - paper or CRO - normal paper speed -30mm/sec For high resolution and of high frequency signal -60mm/sec

36. EMG-Electromyogram Bio electric potential of muscle generated by muscle activity -Muscle fiber generate action potential when excited Measured directly from skin(surface electrode) or penetrating the skin(needle electrode) skin-pick up nearby muscle activity also -Instantaneous sum of muscle potential generated by group of muscles at any given time EMG -function of the amount of muscle activity and electrode placement. Random noise waveform - peak amplitude-50 micro volt to 1mv (depends on distance between electrode and muscle - frequency-10Hz to 3000Hz

37. EMG measurement Unipolar or bipolar measurement is used EMG Amplifier- -High gain (80 to 100db), high input impedance (10M Ω ), , differential amplifier with high CMRR , Frequency range-10Hz to 10KHz -accommodate high frequency band -Upper frequency response is varied by switchable LPF Display - graphic pen - Oscilloscopic read out -to get high frequency response - Storage CRT -retention of data - Oscilloscope camera - visual record of data from CRO

38. Audio amplifier and loud speaker - hear the crackling sound - helpful in the placement of needle and wire electrode into the muscle to ensure that the electrode are making good contact , number of adjacent muscle in contact with the electrode conduction velocity -indicate the location and type of the nerve lesion . -used to examine the nerve function procedure -stimulating nerve segment with electric shock for 0.2 - 0.5 milliseconds - determine the latency Latency - elapsed time between the stimulating impulse and the muscle's action potential. Determination of conduction velocities in motor nerves

39. l 1 – distance between EMG electrode and the stimulating electrode placed on the skin. t 1 - time elapsed (latency) between the stimulating impulse and muscle's action potential - electrodes are repositioned l 2 – new distance between the electrodes, l 1 >l 2 , and t 2 –corresponding latency Conduction velocity v = (l 1 -l 2 )/(t 1 -t 2 ) Normal value-50m/sec, less than 40m/sec- disorder in nerve conduction

40. Quantification of EMG signal 1.Measurement of amplitude -maximum amplitude achieved for given type of muscle activity -depends on location of electrode 2.Count of number of spikes or zero crossing over given interval -number of times the given amplitude exceeds the threshold -vary with muscle activity 3. Time integral of EMG waveform -Measure the integral value of EMG signal over a given time(0.1sec) -related to tension and activity of the muscle 4. Envelope or contour of EMG - EMG signal is rectified, filtered to produce envelope or contour -envelope contains lower frequency band, related to muscle activity

41. Phonocardigram(PCG) -Graphic recording of heart sound PCG - measurement of sounds/murmurs generated by the heart during opening and closing of heart valves -heart disorders diagnosed by sound and vibrations in heart beat and pumping of blood Auscultation- Technique of listening to sounds produced by organs and vessels Normal heart beat produce 2 distinct sound- ‘ lub-dub’

42. Heart sound Sound origin Max energy 1 st sound Lub At the time of QRS complex, Closure of AV, mitral valve(bicuspid valve) and aortic valve open 30 to 45Hz Below audible 2 nd sound dub Occurs at the T wave Closure of aortic valve and mitral valve open 50 to 70Hz Releases blood for pulmonary and systemic circulation 3 rd sound 0.1 to 0.2sec after the 2 nd heart sound Due to rush of blood from atria into ventricle Below 30Hz Weak vibration Only for young adults 4 th sound (atrial heart sound) Occur when atria contract Low amplitude , frequency Not audible, visible by graphic recording

43. Abnormal heart sound -normal heart sound -1/10 th of a sec, murmurs extend the normal -Murmurs heard between normal heart sound due to ( i ) improper opening of valves or regurgitation –valve do not close completely and allows backward flow of blood -sound due to high velocity of blood through small opening (ii) small opening in septum (separation between right and left heart) -push blood from left ventricle to right atria(due to pressure gradient),bypass systemic circulation

44. Measurement of PCG

45. Transducer -microphone -frequency response-5Hz and above 1000Hz Amplifier –2 stages of amplifier with gain 20, 50 respectively Filter- HPF to allow high frequency cutoff to be adjusted for noise prevention Display Pen recorder –in adequate to record high frequency integrator- record envelope of frequency over 80Hz along with actual signal below 80Hz -

46. Microphone -PCG

47. Vibro cardiogram -vibration of sides of the heart as it thumps against the heart wall Apex cardiogram -tip or apex of the heart hitting the rib cage Korotkoff sounds - when artery is partially occluded , the blood velocity increases and leads to the sound Ballistocardiogram -dynamic forces of heart as it beats or pumps blood to major arteries

48. Comparison of bioelectric potential Bioelectric signal Frequency range Voltage range (micro volt) Electrode used Origin Electro cardiogram(ECG) 10 to 100Hz Surface and Needle electrode Heart muscles Encephalogram (EEG) 1 to 100Hz 10-100millivolt Surface and Needle electrode Neuronal activity of the brain Electromyogram (EMG) 10 to 3000Hz 50 microvolt to 1mv Surface and Needle electrode Skin muscles PCG 5 to 100Hz microphone Heart sound