Bio Signal Measurement Flashcards

Question

What do we want from a filter?

Answer 1

1) Brick wall like amplitude response 2) Linear phase response 3) Steep transition between pass and stopband

Answer 2

* -3dB point is fc – corner/cut off frequency * Maximally flat response in the pass band * Gain in stop band ≠ 0 • As n↑, the transition region narrows * Attenuation slope ≈ -20n dB/decade * As n ↑, the amplitude response looks more like the ideal brick wall response.

Answer 3

• BW – flat magnitude response • Bessel – Linear phase response • Tchebyshev – sharp transition region

Answer 4

``` • Offline - Diagnostics - Biomedical research • Online (real time) - Control of assistive devices like prosthesis and exoskeletons - diagnostics ```

Answer 5

* Sampling -> continuous to discrete time * Takes snapshots T seconds apart * Called Pulse Amplitude modulation * Digitisation -> continuous to discrete amplitude * Called Pulse code modulation

Answer 6

• Fh - the highest frequency of the input signal • Fs – sampling frequency • Fourier transform of the sampled signal gives a repeated spectrum (repeats every fs)

Answer 7

-Use a lowpass filter where fc=fh • To avoid spectral overlapping, the fsshould at least be 2fh • This is the Nyquist sampling criterion • Practically, we always take fs >2fh

Answer 8

* Aliasing = confusion * Aliasing happens when the signal is under sampled. * Spectral folding – gives a distorted signal upon recovery.

Answer 9

* If under sampled, the recovered signal doesn’t look anything like the original. * Band-limiting the signal prior to sampling can prevent aliasing –Anti aliasing filters * There is a trade off between aliasing error, filter order and sampling frequency.

Answer 10

• Uses a number of discrete amplitude levels to represent a continuous amplitude range. ``` • Pulse code modulation - Finite number of code words (Q) - Number of symbols = m - Code word length = n - Number of possible codewords 𝑄 = 𝑚^n ```

Answer 11

• SNR = Signal power/ Noise power • SNR due to Quantization using the ADC - SNR for Gaussian input=6N-4.7 dB - SNR for sinusoidal input=6.02N+1.76 dB

Answer 12

quantisation error noise=q/sqrt(12)

Answer 13

``` -Effective number of bits • To calculate ENOB • Measure input signal power • Measure Noise power ( difference between power of the full frequency spectrum and the input signal power) • Calculate the SNR based on measurement • 𝐸𝑁𝑂𝐵 =(𝑆𝑁𝑅𝑚𝑒𝑎𝑠𝑢𝑟𝑒𝑑 −1.76)/6.02dB ```

Answer 14

The discipline that deals with the detection, acquisition, processing, analysis and use of the electrical signals that emanate from contracting muscles. EMG- plot of myoelectric voltage vs. time

Answer 15

• Index of muscle activity - EMG gives an indication of the output force of a given muscle - EMG signal amplitude increases for increasing output force - Activity relative to MVC (Maximum Voluntary contraction) • Muscle Fatigue index - Fatigue is a specific phenomenon in which the muscle force decreases due to prolonged activity - Fatigue causes a shift in the frequency content in the EMG, and also reduces the conduction velocity within the fibre

Answer 16

• Assessment of muscle pathologies - Lower back pain - Distinguishing between Parkinson tremors and essential tremors • Control of powered Limb prostheses

Answer 17

Single Fibre Action potential • Electrodes measure the change in the dipole

Answer 18

* The time between the firings Ti is not equal * Ti is a random variable with mean of 20ms to 200ms (depending on the force output), and a variation (SD ~ 10-20% of the mean) * Ti can thus be modelled as a gaussian random variable

Answer 19

– group of muscle fibres with a common nerve axon • All fibres in a motor unit fire synchronously • Innervation Zone • SFAP for each fibre will depend on: - Position of the end plate - Velocity of the action potential

Answer 20

* MUAP = Collection of all fibre signals * Larger in magnitude * Large time duration * Waveform is different from SFA

Answer 21

• Relative geometry of electrode and muscle fibres in the motor unit in its vicinity • Position of detection surface relative to the innervation zone • Size of the muscle fibres (amplitude is proportional to the diameter of the fibre) • Number of muscle fibres in the motor unit

Answer 22

* To sustain a muscle contraction, the motor units must be activated repeatedly. * The resulting sequence of MUAP of a single Motor unit is called MUAPT. * The MUAP within a MUAPT will remain constant if the geometric relationship between the electrode and the active muscle fibres remains the same

Answer 23

time between adjacent MUAP ``` -Mathematically, can be expressed as a sequence of Dirac delta impulses convoluted with a filter representing the shape of the MUAP ```

Answer 24

• EMG signal = linear summation of the MUAPTS (from a number of motor units)

Answer 25

1. Rectification (half or full wave) 2. Mean absolute value 3. Integration 4. Root mean square

Answer 26

- Power spectrum density of signal (from FFT) - Useful measures of the PDS are median frequency, mean frequency and the bandwidth of the spectrum - Median frequency is less sensitive to noise - Frequency spectrum parameters are appropriate for analysing signals that are stationary or almost stationary.

Answer 27

• ECG = surface level measurement of the electrical activity of cardiac muscles. • Also known as EKG • Cardiac electrogram – when electrodes are placed on or in the heart to measure the electrical activity. • Self excitation property (don’t need a nerve to initiate the firing) • The muscle fibres fire more or less synchronously

Answer 28

- Those groups of cells that have the ability to pace the heart. - 3 such groups - SA node, AV node, Bundle of His & Purkinjee fibre

Answer 29

1. Rest phase – atria fill with blood. There is no electrical activity. 2. The SA node depolarizes spontaneously, and waves of depolarization move from the SA node across the atria – causing a mechanical contraction pushing the blood into the ventricles 3. AV node then delays the depolarization spread to ensure that the ventricles are filled 4. Purkinjee fibres conduct the depolarization wave very rapidly – causing the ventricles to contractfrom the bottom upwards. (Ventricular depolarization) 5. Ventricles repolarize (T wave) and return to the rest phase.

Answer 30

the shape, duration, amplitude, etc of the ECG as | compared to the normal ECG to detect diseases.

Answer 31

ECG lead – is a graphical description of the electrical activity and is computed by analysing electrical currents detected by several electrodes.

Answer 32

12 lead display – has 12 curves derived from 10 electrodes that are placed on standard location. * 6 leads come from 4electrodes placed on the limbs. * 6 leads come from the 6 electrodes placed on the chest.

Answer 33

• All the limb leads use the electrode on the Right leg to be the ground electrode. - Standard electrode leads are (1) RA – LA (2) RA – LL (3) LA - LL

Answer 34

• Augmented limb leads use stand limb electrode configuration, but the electrodes are connected through resistors to a common node. • This decreases the noise level and increases the size of the apparent signal.

Answer 35

* Leads I, II and III form the original leads constructed by Wilhelm Einthoven. * Their spatial orientation forms a triangle in the chest. • Based on Kirchoff’s current law: 𝐿𝑒𝑎𝑑 𝐼 + 𝐿𝑒𝑎𝑑 𝐼𝐼𝐼 = 𝐿𝑒𝑎𝑑 𝐼𝐼 only need info from two leads

Answer 36

``` • Bandwidth: 0.1 – 100 Hz • Gains: between 100 to 5000 (usually much smaller than EMG as the signal is larger) • CMRR: 100 dB or above • Input resistance: >100 MΩ ```

Answer 37

ST segment acts as marker

Answer 38

• Electrical activity of the brain as | measured from the scalp.

Answer 39

(Electrocorticogram)– the electrodes are placed on the exposed surface of the brain (cortex)

Answer 40

Depth recording – when electrodes are advanced into the brain.

Answer 41

“10” and “20” refer to the % distance between the adjacent electrodes (of the front to back or the right to left distance on the skull)

Answer 42

* Gamma has the highest bandwidth – only between 25 to about 40Hz. * Frequency content of EEG is much lower than that in EMG or ECG.

Answer 43

-sleep studies - (Study brain waves in relation to sleep) • We go through different stages of sleep as we sleep through the night, and each stage plays a different role in the proper brain function. Eg: Stage 3 & 4 – body recuperates, Stage 2 –memory consolidation.

Answer 44

• The action potential in a muscle fibre is the signal for the fibre to contract or generate a force. • Muscle fibre contraction occurs when specialized, regularly arranged proteins – actin and myosin – form linkages (called cross bridges) and slide past each other.

Answer 45

• The muscle twitch lasts much longer than the action potential.

Answer 46

- Action potential in one axon, generates a twitch in all the muscle fibres that it innervates. - (1) If more axons are activated, then more force is produced by the twitch. - (2) If the same axon is stimulated more frequently, the twitches fuse into a `tetanic contraction.

Answer 47

– number of axons that are stimulated, and the frequency of stimulation of each axon.

Answer 48

The higher the firing rate, the higher the steady-state force. (up to saturation – called tetanic contraction)

Answer 49

* The size principle states that as more force is needed, motor units are recruited in a precise order according to the magnitude of their force output. * Small units are recruited first –exhibiting task appropriate recruitment

Answer 50

- Minimises amount of fatigue experienced by using fatigue resistant first, and only using the fatigable fibres when high forces are needed. - The relative change in force produced by additional recruitment remains relatively constant.

Answer 51

Mean Frequency and conduction velocity both decrease when a person is fatigued.

Answer 52

* Most advanced upper-limb fitting clinic in Canada * Myoeelctric/powered upper limb prostheses * Custom prosthetic devices * > 120 clients

Answer 53

• Electrical activity from a residual limb is amplified, processed and used to control the flow of electricity from a battery to a motor, which operates an artificial limb.

Answer 54

• Must be comfortable -> weight should be minimised • Work reliably • Have a natural appearance during rest and during functional activities • Should replace not only the mechanical function, but also the cutaneous and the kinaesthetic sensation. • Clinical acceptance – ease of fitting, adjustment and training • Versatility – usually achieved through modular design

Answer 55

• On/Off control - One or two control sites - Voluntary open and automatic closing/ or voluntary opening and closing -device was not portable, before invention of transistors

Answer 56

* Mapping individual EMG signalsto individual functions of a prosthetic device * Good performance * Intuitive for user

Answer 57

- Usually not a physiologically appropriate mapping - limited number of control sites - Control of limited number of DOF