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Biomedical Signal Analysis > Biomedical Signals > Flashcards

Biomedical Signals Flashcards

1
Q

What is resting potential?

A

In excitable cells like a neuron or muscle cell
- RP is the electrical potential difference (voltage) between the inside and outside of the cell.
- semipermeable membrane (=some ions can move in and out, some can not depending on the state of the cell and the voltage-gated ion channel.
- body fluids: conductive solutions containing ions
- RP ~ -60 mV to -100 mV

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2
Q

Describe the state of equilibrium of a cell.

A

In the resting state, the membrane of excitable cells
- permit entry of K+ and Cl-
- block Na+ ions
- equilibrium acc. to charge and concentration –> with a potential difference (RP)
- inside of the cell is negative (-) w.r.t the outside
- until some disturbance or stimulus upsets the equilibrium

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3
Q

What is an action potential?

A
  • the basic component of all bioelectrical signals
  • an electrical signal that accompanies the mechanical contraction of a single cell when stimulated by an electrical current (neural or external)
  • Depolarization: Na+ influx, K+ outflux –>net (+), peak +20mV (most cells), +40mV (heart muscle cells)
  • Repolarization: net efflux of K from the cell, inside more negative –> RP
  • Nerve and muscle cells repolarize rapidly ~ 1ms
  • Heart muscle cells repolarize slowly 150 ms - 300 ms
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4
Q

What is the absolute/relative refractory period?

A

The absolute refractory period is a period during which a cell cannot respond to any new stimulus after an action potential. (in nerve cell ~1ms)
This is followed by a relative refractory period, during which another AP may be triggered by a much stronger stimulus than a normal situation. (in nerve cells 3-5ms)

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5
Q

What is saltatory conduction?

A

The propagation of AP as a current flows by jumping from one node to the next node of Ranvier along myelinated nerve fibers.

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6
Q

What can ENG be used to measure?

A

the velocity of propagation (or conduction velocity) of a stimulus or AP in a nerve.

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7
Q

What is ENG?

A

Electroneurogram
the electrical signal observed as
- a stimulus
- and the associated nerve AP propagates over the length of a nerve.

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8
Q

How can we measure ENG?

A
  • concentric needle electrodes
  • or silver-silver-chloride electrodes (Ag-AgCl)
    • at the surface of the body
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9
Q

How can peripheral nerve conduction velocity be measured?

A
  • stimulating a motor nerve
  • measuring the related activity at 2 points that are a known distance apart along its course.
  • stimulus 100V, 100-300 microseconds
  • ENG amplitude 10 microVolt
  • amplifier: gain 2000, bandwidth 10 Hz - 10000 Hz
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10
Q

How much is the typical conduction velocity in nerve fibers?

A

45-70 m/s

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11
Q

Give an example of using ENG to measure conduction velocity.

A
  • experimental limb: forearm
  • recording sites: from the elbow to the wrist
  • note: relaxed posture –> minimize muscle contraction and other undesired effects
  • short stimulus ~ 100V, in 100-300 microseconds duration
  • record the difference in the latencies of the ENGs –> conduction time
  • repeat measurement 3 times (or more)
  • the known distance between the recording sites
  • conduction velocity (m/s) = distance / time
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12
Q

What is EMG?

A
  • electromyography
  • measures muscle response or electrical activity in response to a nerve´s stimulation of the muscle.
  • recorded using needle electrodes or Ag/AgCl electrodes at the body surface
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13
Q

How does skeletal muscle work?

A
  • Skeletal muscle fibers are twitch fibers.
  • produce a mechanical twitch response for a single stimulus
  • generate a propagated AP
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14
Q

What is a motor unit?

A
  • motor unit = MU
  • the smallest muscle unit that can be activated by volitional effort
  • consisting of :
    1. an anterior horn cell ( or motoneuron, from a spinal cord cross-section)
    2. its axon
    3. all muscle fibers innervated by that axon
      –> the constituent fibers of a MU are activated synchronously
      –> extend lengthwise in loose bundles along the muscle
      –>interspered with the fibers of other MUs
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15
Q

What is SMUAP?

A
  • single motor unit action potential
  • upon stimulation,
  • each MU contracts –> causes an electrical signal
  • summation of the APs of all its constituent fiber cells
    => mechanical output (contraction) = net result of stimulation and contraction of several of its MUs
  • normal SMUAPs usually have biphasis or triphasic waveform
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16
Q

How can we measure a single motor unit?

A

–> measure muscle fibers at the interested point correlating to an interested movement

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17
Q

What are the factors that can affect the shape of recorded SMUAP?

A
  • needle electrode type used
  • its positioning w.r.t the active MU
  • the projection of the electrical field of the activity on the electrodes
    e.g. SMUAP trains recorded simultaneously from 3 needle electrode channels at different locations –> 3 different MUs are active –> the same SMUAP shows different shapes due to the projection onto the 3 channel axes
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18
Q

What is the innervation ratio?

A
  • number of muscle fibers per motor nerve fibers / MU
  • e.g.
    large muscle –>gross movement: 100s of fibers/MU
    small muscle –>precise movement: fewer fibers /MU
    + platysma (neck) muscle: IR of 25
    + first dorsal interosseus (finger)muscle: IR of 340
    + medail gastrocnemius (leg) muscle: IR of 1934
19
Q

Describe a physiological model for EMG signal generation.

A
  • Each motoneuron from the spinal cord branches each axon to muscle fibers through nerve fibers.
  • Each motor neuron fires and can be represented by an impulse train.
  • Firing activates MU represented by system hi(t)
  • MU generates a train of SMUAPs
  • Net EMG is a sum of several SMUAP trains represented as mp(t,F)
    –> the observed EMG is a function of time t and muscular force produced F –> m(t,F)
20
Q

How is the shape of SMUAP affected by diseases?

A
  • higher rate (at low-to-medium levels of effort)
  • polyphasic
  • large amplitude
21
Q

How does neuropathy affect the shape of SMUAPs?

A

Neuropathy due to:
+ damage to nerves
+ slow conduction of fibers in 1 MU
+ desynchronized activation of fibers within 1 MU
+ polyphasic SMUAP within an amplitude larger than normal
=> the same MU may fire at higher rates than normal before more MUs are recruited

22
Q

How does myopathy affect the shape of SMUAPs?

A

Myopathy due to:
+ loss of muscle fibers in MUs, neurons intact
+ patchy destruction of fibers (muscular dystrophy)
+ size of MU is reduced
+ asynchrony activation
+ splintering of SMUAPs occurs / polyphasic SMUAPs
=> more MUs than normal recruited at low levels of effort

23
Q

What is Gradation (gradation of muscular force)?

A
  • control of muscular contraction levels
  • 2 neural mechanisms responsible
    + recruitment = spatial summation of activated MUs –> increasing Nr. of MUs activated/recruited –> increasing amount of force required during movement
    + rate coding = temporal summation of activated MUs —> higher frequencies of discharge (firing rate) of each MU with increasing effort –> greater tensions
24
Q

During contraction, are the responsible MUs activated at the same times/frequencies)

A

No
- MUs activated at different times & frequencies = asynchronous contraction
- Timing:
+ twitches of individual MUs sum and fuse to form tetanic (sustained) contraction and increased force
- Rate/Frequency
+ weak volitional effort: 5-15 pps (pulses per second)
+ at greater tension: 25-50 pps

25
Q

What are the important characteristics of EMG signals?

A
  • spatiotemporal SMUAP summation of all active MUs
  • signals obtained with surface electrodes are
    + complex (interference patterns of several MUAP trains)
    + difficult to analyze
  • used to research
    + neuromuscular diseases (neuropathy, myopathy)
    + biomechanical relationships (motor control) e.g. understanding Parkinson disease
    + control signal (prosthetic devices)
26
Q

What is ECG?

A
  • electrocardiogram
  • electrical manifestation of the contractile activity of the heart
  • recorded with surface electrodes on the limbs or chest
27
Q

What can affect ECG waveshape?

A

By cardiovascular diseases e.g. myocardial ischemia and infarction (heart attack)
By abnormalities such as ventricular hypertrophy or conduction problems.
* ventricular hypertrophy = thickening of the heart ventricle wall

28
Q

What is the normal heart rate (HR)? What controls it?

A
  • Normal resting HR ~ 70bpm, 60-90ml/beat, 5-7l/min
  • At work HR ~190bpm, ~120ml/beat, 23l/min
  • Controlled by specialized pacemaker cells in the sinoatrial node (SA node)
  • The firing rate of the SA node controlled by the autonomous nervous system leading to the delivery of the neurotransmitters
    + acetylcholine for vagal stimulation (reduced HR)
    + epinephrine (=adrenalin) for sympathetic stimulation (increased HR)
  • SA provides the base rhythm, changed by external controls
29
Q

How is HR controlled by external innervation?

A
  • Nerves to heart:
    + visceral sensory fibers
    + parasympathetic branches of vagus nerve (decreases HR)
    + sympathetic fibers from the thoracic spinal cord (increases HR and force of contraction)
30
Q

What is the difference between the motor neurons innervating skeletal muscles and visceral muscles/cardiac muscles?

A

Skeletal& branchial muscles:
- Either somatic or branchial motor neuron synapse onto muscle
- involve only 1 motor neuron –> monosynaptic
Visceral muscle/ cardiac muscle
- General visceral motor neurons innervate the muscles
- involve 2 motor neurons –> disynaptic

31
Q

What are other factors that can affect HR?

A

illness or cardiac abnormalities
bradycardia - abnormally low HR <60bpm
tachycardia - high resting HR

32
Q

What is CP?

A
33
Q

What is PCG?

A
34
Q

What is EEG?

A
35
Q

What is ERP?

A
36
Q

What is EGG?

A
37
Q

What is VMG?

A
38
Q

What is VAG?

A
39
Q

What is BCG?

A
40
Q

What is HSS?

A
41
Q

What is CTG?

A
42
Q

What is the end goal of Biomedical Signal Analysis?

A
  • aims to aid more accurate diagnostic decisions by the physician
43
Q

Why do we need computer-aided diagnosis (CAD)?

A

Biomedical Signal Analysis (7 decks)

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