Diagnostic Devices for Nervous System PDF

Lecture 6. Diagnostic Devices for Nervous System Introduction to Biomedical Engineering Technology Boreom Lee [email protected] , X 3272 Department of BioMedical Science and Engineering Gwangju Institute of Sciences and Technology Copyright. Most figures/tables/texts in...

Lecture 6. Diagnostic Devices for Nervous System Introduction to Biomedical Engineering Technology Boreom Lee [email protected] , X 3272 Department of BioMedical Science and Engineering Gwangju Institute of Sciences and Technology Copyright. Most figures/tables/texts in this lecture are from the textbook “Introduction to Biomedical Engineering Technology by Laurence Street 2016” and this material is only for those who take this class and cannot be distributed to anyone without the permission from the lecturer.  Nervous System Nervous signal conduction through the body (two processes) – Within nerve cells Transmitted in long cell extensions called axons Not as simple as an electrical signal in a wire ∵Cell membrane along the axon must be polarized and then depolarized as the signal passes along A time lag or refractory period Overall conduction speed within an exon: 50-200 m/s – Far slower than the near-speed-of-light conduction of electrical signals in a wire 2 Nervous System 3  Nervous System Nervous signal conduction through the body (two processes) – From one cell to another Passed through a connection called synapse Connect two nerve cells to simply pass a signal along Others can actually inhibit signal transmission within the target axons An interface btw nerve axons and muscle cells = neuromuscular junction – Neurotransmitter: acetylcholine (Ach) – Acetylcholinesterase: break down Ach in order for muscle to relax 4  Nervous System Drugs affecting nervous system – Agonists Excite the nervous system Caffeine, cocaine, ecstasy, and amphetamines – Antagonists Inhibit the nervous system Alcohol, valium, barbiturate, marijuana, heroin and its derivatives Some nerve gases(e.g., sarin)/pesticides (e.g., DDT and parathion) – Inhibit the action of acetylcholinesterase – Cause muscle to remain contracted for prolonged periods in spasms  painful death 5  Nervous System Anesthetics – Local anesthetics Act by blocking motor and sensory synapse in the area of application Procaine, xylocaine, and benzocaine – General anesthetics Blocking ion channels in the nervous system  blocking pain and producing unconsciousness – Devices to test the effectiveness of anesthetics Nerve stimulators BiSpectral index monitors 6  EEG Monitors and Machines Abnormalities within the brain – Structural abnormalities  epilepsy and other seizures, aphasia, hallucinations, and comas – Disease processes: tumors, Parkinson’s disease, cerebral palsy  extreme difficulties for patients Diagnosing tools – Electroencephalogram (EEG): almost the only tool available in the past – Imaging equipment: CT, MRI or PET scanners – Electrical activity of the brain measured in real time Provide information that other source cannot Confirm or expand on the results of other tests 7  EEG Monitors and Machines EEG machine – A set of a dozen or more electrodes – placed in specific locations on the scalp – Connected to amplifier/digitizer/analyzer/display/recorder unit (similar to ECG systems) – Signals: stored and analyzed later and/or printed out on a recorder strip – Electrodes for special studies Inserted through the skull and directly into brain tissue Precise determination of the location of anomalies 8 EEG Monitors and Machines 9  EEG Monitors and Machines Waves of signals recorded from brain electrical activity – Groups divided according to their characteristics 10  EEG Monitors and Machines Waves of signals recorded from brain electrical activity – Alpha waves Range: 9 to 14 Hz Relatively high amplitude Seen when the subject is awake but relaxed – Beta waves 15 – 40 Hz Lower amplitude, but higher frequency than alpha waves Subject is aroused in some way: angry or frightened, or closely involved in a conversation or activity 11  EEG Monitors and Machines Waves of signals recorded from brain electrical activity – Theta waves A variation in amplitude (usually greater than beta waves) Low frequency: about 4-8 Hz Periods of inattentive consciousness (e.g., daydreaming) – Delta waves Highest in amplitude but lowest in frequency About 1.5 – 4 Hz Periods of sleep Can be analyzed to indicate depth of unconsciousness during general anesthesia 12 EEG Monitors and Machines 13  EEG Monitors and Machines Absence of brain wave activity: a legal indication of brain death in some jurisdictions EEG activity changes by various stimuli – Flashing and/or colored lights or various sounds – Abnormal responses – can indicate various brain abnormalities – In epilepsy study Can induce seizures under controlled conditions – Using flashing lights with controlled frequency (around 16-25 Hz) and intensity Photosensitivity: only about 5% of epilepsy patients 14 EEG Monitors and Machines 15  EEG Monitors and Machines Learning to control some aspects of brain waves – Biofeedback training Useful in stress or pain reduction Useful in focusing concentration – Controlling external devices By altering brain waves in a particular manner With suitable analysis and interface circuitry – BCI (brain-computer interface) – BMI (brain-machine interface) 16  BIS Monitors A special application of EEG technology to evaluate the depth of unconsciousness of patients Useful during general anesthesia or when patients are being kept in an induced coma – Under general anesthesia Too high level of consciousness – Patients can experience awareness during surgery  very distressing! Too low level – Prolonged recovery from anesthetic – Physiological damage in extreme cases 17  BIS Monitors Useful during general anesthesia or when patients are being kept in an induced coma – Induced coma To help keep a patient immobile when recovering from various traumas A balance btw too high and too low depths of unconsciousness (as with general anesthesia) 18  BIS Monitors BiSpectral index monitor (BIS) – EEG signals from a few specifically placed electrodes – BIS value Produced by analyzing EEG with a complex algorithm A unitless number that corresponds to level of consciousness – 0: brain death – 100: full consciousness and awareness 19 BIS Monitors 20  Muscle/Nerve Stimulators Circumstances in which it is necessary to greatly relax or paralyze a patient’s muscles – During surgical procedures: the signals produced by ESU(electrosurgery machine) action  cause muscle contractions in various areas of the body – Some surgeries involving muscles – much easier when the muscles being worked on are relaxed – On ventilators: patients may fight the action of the machine if their breathing muscles are active – In electroconvulsive therapy (ECT): ECT pulse can cause extreme contractions in many muscle groups  injuries to patient or staff 21  Muscle/Nerve Stimulators Across neuromuscular junction – Nerve signal transmitted via Ach – Muscle relaxing agents: block the action of Ach  muscle activity reduced Sufficient degree of inhibition to prevent unwanted muscle activity Excess dosages – avoided Nerve/muscle stimulator – Calibrated signals applied to a patient’s skin in a convenient location near a muscle group(thumb or big toe) – Once over a certain threshold: the signals cause muscle contraction to a degree corresponding to the signal amplitude 22  Muscle/Nerve Stimulators Nerve/muscle stimulator – A certain high value of stimulus Muscle contraction – the greatest possible Adding about 10% to this stimulus level (a supramaximal stimulus): maximal muscle contraction ensured – Muscle relaxant administration Supramaximal stimuli delivered until such time that muscle action is reduced to a certain percentage of maximum (e.g., 20%) Can be leveled or reduced in order to maintain the desired reduction in muscle response – Setting Pulses of various amplitudes and durations Pulses delivered in continuous trains or in bursts of a specific number of pulses 23 Muscle/Nerve Stimulators 24