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Slide 3A
- Stroke can definitely be confirmed by a) MRI b) EEG c) Motor movement d) Speech e) CT scan
- Epileptic seizures can definitively be confirmed by a) Heart rate in Apple watch b) Video (movement) c) Convulsion d) MRI e) EEG
- There is a traffic accident. The person is found to be “non-responsive” with no pulse and no evident chest movement. You don’t have any equipment, so what would you do? a) Take body temperature b) Scream, get attention c) Give CPR d) Try to elicit pain response, reflex e) Call ambulance and wait
- Neurostimulation (modulation) has been used to treat – select the incorrect answer a) Alzheimer b) Depression c) Parkinson’s d) Epilepsy e) Arthritis and inflammation
- What would be the key equipment in an ambulance or in emergency field situations a) Pacemaker b) Defibrillator c) Brain machine interface d) Portable CT scanner e) Blood chemical analyzer
- How would you detect someone having the following:
- Brain injury or brain death after cardiac arrest:
Check for heartbeat. unconsciousness will occur rapidly once the heart stops beating, typically within 20 seconds.
The question isn’t clear enough, so I’ll take 2 approaches for the answer under the common assumption that all medical devices are available
- The victim is still in coma
Using pupillary assessment, brain injury could have taken place if the pupils are unequal (difference in diameters >1mm), with 1 pupil being dilated and non reactive to light, or if pupils are pinpoint bilaterally and too small to observe reaction to light, or if normal-sized pupils alternate between dilation and constriction in response to light. If pupils are dilated bilaterally and do not respond to light stimulus or the response differs between pupils, there’s a chance that brain death has occurred.
EEG is also a good diagnostic tool for brain injury and comatose outcome prediction
3A slide 3
ICU: Cortical Health Index (CHI) for monitoring global brain injury in
post-cardiac arrest patients with bedside monitor to enhance clinical
management (treatment/counseling)
Intracranial mass lesion/TBI: 1st non-invasive bedside assessment of patients
with acute mass lesions in the neurocritical care unit (vs. ICP monitoring)
3C slide 5 - Neuromonitoring for confirmation of Brain Death
SSEPs: commonly used to assess after Cardiac Arrest (CA)
Bilateral absence of the N20 response between 4 and 72 hours after CA
predicts poor prognosis in patients without prior hypothermia with ~100%
accuracy.
Reports do exist of patients who initially have absent N20 responses who
proceed to recover these responses, as well as achieve a good recovery.
3D Slide 20
Record the EPs of repeated time-synchronized experiments and observe the
temporal coherence. A low coherence can indicate neurological injury.
Use cortical Injury Monitor device
- The victim has been resuscitated and is conscious
NICU: Neonatal CHI monitoring HIE and seizures in post-asphyxia babies via bedside monitoring in the NICU
3. Stroke:
i. Face drooping. One side of the face droops or is numb. When asked to smile, the person’s smile looks uneven. ii. Arm weakness. One arm will feel weak or numb. When asked to raise both arms, one of the person’s arms will drift downward. iii. Speech difficulty. The person will have trouble speaking. Speech will sound slurred, or the words will be hard to understand. When asked to repeat a simple sentence like “The sky is blue,” the person will have trouble repeating it correctly. iv. Numbness or weakness in the face, arm, or leg, located on one side of the body. Because our brains control each side of the body from a different hemisphere, a stroke usually affects one half of the body. v. Confusion or trouble understanding. If you suddenly feel confused and have trouble understanding things you usually have no problems managing, it could be a sign of stroke. vi. Trouble seeing in one or both eyes. A stroke can affect the area of the brain that manages vision. A sudden loss of vision is another sign of stroke. vii. Sudden dizziness, trouble walking, loss of balance or coordination. The keyword here is sudden: one moment you’re fine, the next you feel dizzy or have trouble keeping your balance. This is another sign that your brain is being affected by something. viii. Sudden and severe headache with no obvious cause. A stroke can cause a sudden, very bad headache that doesn’t seem related to your usual headache triggers.
- How would you detect depth of anesthesia? This is a situation where a patient is anesthetized and you want to know deeply is the patient sedated, and that the patient does not feel pain/memory etc.
- Heart rate variability (can indicate DoA)
Brain electrical activity monitoring - most can indicate DoA with a defined scale, but some can’t reliably identify the transition from being conscious to unconscious
- Spontaneous EEG activity monitor - BIS, entropy, narcotrend
Bispectral Index (BIS) is empirically derived from EEG to indicate the depth of anesthesia on a scale of 0 (EEG silent/ flat) to 100 (awake CNS). The BIS is calculated from an algorithm that relates three factors: (1) degree to which EEG waveforms are in phase (bico-herence); (2) amount of EEG power in the delta (1– Hz) versus beta (13–30 Hz) range (power spectrum); and (3) proportion of the EEG
that is isoelectric. The degree of bicoherence of the EEG increases with increasing anesthetic depth (Fig. 7.2) and is inversely related to the derived BIS.
Entropy - acquisition and processing of raw EEG and FEMG (facial electromyography) signals by using the Entropy algorithm. The commercially available Datex-Ohmeda module calculates entropy over time windows of variable duration and reports two separate entropy values. State entropy (SE) is an index ranging from 0 to 91 (awake), computed over the frequency range from 0.8 to 32 Hz, reflecting the cortical state of the patient. Response entropy (RE) is an index ranging from 0 to 100 (awake), computed over a frequency range from 0.8 to 47 Hz. Not clinically evaluated for intraoperative awareness.
Narcotrend - dimensionless Narcotrend index from 100 (awake) to 0 (electrical silence).
Patient State Index (PSI) derived from a four-channel EEG. The derivation of the PSI is based on the observation that there are reversible spatial changes in power distribution of quantitative EEG at loss and return of consciousness. The PSI has a range of 0-100, with decreasing values indicating decreasing levels of consciousness or increasing levels of sedation
But BIS and PSI (patient state index) don’t reliably detect the transition from consciousness to unconsciousness, same goes for Narcotrend
SNAP index" ranges from 100 (arbitrarily representing the fully awake state) to 0
- Depth of anesthesia
Refer to the previous question
- What signal processing method would you use to improve the signal to noise ratio of evoked potentials?
3D slide 16
Coherent Averaging improves signal to noise ratio Steps: Apply electrodes to scalp Amplify signal Record EEG Sensory stimulation
Record multiple epochs Signal average SNR goes up sqrt(N) … N trials
- Perform repeated time-synchronized experiments and apply ensemble averaging
- Principal Component Analysis
- What are the different stimuli that can you stimulate the nervous system to evoke cortical evoked responses?
An evoked potential or evoked response is an electrical potential recorded from the nervous system of a human or other animal following presentation of a stimulus:
Somatosensory Audio Visual Motor
Slides 3B
Study question: What are the differences between cardiac and neural action potentials?
What are the important ion channels?
- Hyperpolarization occurs almost immediately after the peak of neural AP because
Na+ voltage-gated channels closed and K+ V-gated channels open.
- After the peak of cardiac AP, Ca+ion influx causes depolarization in conjunction with
K+ outflux, leading to a long delay in repolarization as compared against neural AP
Study question: How would you measure nerve conduction velocity?
When the Achilles tendon is stretched after being tapped with a reflex hammer, the induced
action potential is conducted up the leg to the spinal cord and back down where it causes
the gastrocnemius (calf) muscle to contract. To determine the speed of conduction, the
impedance, and so on. In addition, the amplifier system should be designed for small
magnitude EEG signal (key features: high gain, low noise, suitable bandwidth).
- Identify novel/useful applications of EEG recording or monitoring
sleep studies (sleep stage analysis), brain disorders like seizures, monitoring in neurocritical
care units and before/after surgery.
- What are the pros and cons of using EEG as a way to detect a driver falling asleep on the wheel.
Ans: pros: The Electroencephalogram (EEG) is the physiological signal most commonly used
to measure drowsiness. The EEG signal has various frequency bands, including the delta
band (0.5–4 Hz), which corresponds to sleep activity, the theta band (4–8 Hz), which is
related to drowsiness, the alpha band (8–13 Hz), which represents relaxation and creativity,
and the beta band (13–25 Hz), which corresponds to alertness [ 10 , 59 , 60 , 62 ]. A decrease in
the power changes in the alpha frequency band and an increase in the theta frequency band
indicates drowsiness. Akin et al. observed that the success rate of using a combination of
EEG and EMG signals to detect drowsiness is higher than using either signal alone. Results
are reliable and accurate
cons - Because the level of drowsiness is measured approximately every 5 min, sudden
variations cannot be detected using subjective measures. Another limitation to using
subjective ratings is that the self-introspection alerts the driver, thereby reducing their
drowsiness level. In addition, it is difficult to obtain drowsiness feedback from a driver in a
real driving situation. Therefore, while subjective ratings are useful in determining
drowsiness in a simulated environment, the remaining measures may be better suited for the
detection of drowsiness in a real environment. Intrusive technique.
- What instrument is used to measure the magnetic field from the brain? Magnetoencephalography
B) What are the possible advantages and disadvantages of the magnetic versus electrical measurement?
An advantage of MEG is that magnetic signals are much less dependent on the conductivity of the extracellular space than EEG. The scaling properties (that is, the frequency versus power relationship) of EEG and MEG often show differences, typically in the higher-frequency bands. These differences may be partly explained by the capacitive properties of the extracellular medium (such as skin and scalp muscles) that distort the EEG signal but not the MEG signal.
C) To your knowledge, what breakthroughs in the scientific world that have occurred (or ought to occur?) that would make magnetic field measurement more feasible and affordable?
- Cheap, biocompatible materials that can create durable coating for magnetic materials
- Cheap, biocompatible and/or biodegradable materials that are magnetic in nature
D) If you had a cheap magnetic field sensor (with a relatively lower sensitivity) available what other biomedical application would you think of (other than biopotential measurements).
- They could be used for monitoring transplants with metallic parts, predict their failures
- Another possible application is removing thromboses or tumor in conjunction with nanobots
Slides 3D
- Question: Evoked potentials can be generated by giving
Answers:
A. Electrical stimulus B. Magnetic stimulus C. Auditory stimulus D. Visual stimulus E. All of the above
- Question: Evoked potentials can be noisy. How can the noise be reduced.
Answers:
A. Filtering B. Move less C. Do advanced Fourier or wavelet analysis D. Signal average E. Increase the stimulus strength
- Question: In an operating room, evoked potentials may be useful to detect
Answers:
A. Injury to a nerve or spinal cord and loss of integrity or continuity
- Spectral filters - high-pass, low-pass, band-pass, Notch filters, Finite & Infinite Impulse Response, minimum-phase filters
- Rate-changing filters - e.g. resampling
- What are different applications of brain monitoring? Where in the hospital would you find an EEG monitor?
3A Slide 4
- Predict (e.g. seizure onset)
- Detect/ Diagnose (e.g. ischemia)
- Assess (e.g. depth of Anesthesia)
- Prognosticate (e.g. Hypothermia in Spinal Cord Injury, qEEG in CA, poor outcome in coma)
- Confirm/Validate (e.g. Trauma Brain Injury, Sleep Apnea)
Intesive Care Unit, Operation Room
EEG lab
Q1. What electrodes were used (comment on nature/type of electrodes)? What are the critical requirements for making good measurements? How could the electrodes be improved?
Q2. What recording systems were used (nature/specification of instrumentation)? What specifications are important for good EEG recording?
Q3. What signal processing methods may be used to analyse the EEG signals? Comment on the obvious/common approach: a) filtering, and b) spectral analysis. Describe each of these analysis steps in detail. Review literature to also identify (one paragraph) an alternative method.
Clinical qns
Research and learn about “other” applications of EEG recordings
● Electrocorticogram (e.g. epilepsy surgery) ● Brain computer interface (patients with ALS or paralysis) ● Epilepsy detection and prediction
Research problem: Research and describe an algorithm or a measurement technique to detect epileptic seizures.
● Sleep detection (driving?), ● sleep stages (for disorders)
- How can different sleep stages be automatically identified?
- How would you design a sleep alarm and what would be the benefits or applications? ● Reading the mind (thoughts, dreams) ????? ● hypoxic-asphyxic injury - fusion (no large energy discharges and low volatility, speed of recovery is crucial.. How fast we get to fusion is critical if you pass through a bursting stage) - volatility index
