تحريك الكتريكي بافتهاي تحريك پذير

تحريك خارج سلولي

).Activating Function(تابع فعال ساز �

):برحسب قرارگيري الكترود(نوع تحريك �

.Bipolarدوقطبي �

.Unipolar يا Monopolarتك قطبي �

.Field Potentialميداني �

STRENGTH-DURATION CURVE

� Capacitive membrane.

� Effect of leakage currents.

� Rheobase: Leakage of membrane.

� Chronaxie.

PW

QI ThresholdThreshold =

� Chronaxie.

� Human motor nerve: 0.01ms

� Pain receptors: 0.25ms

� Cardiac muscle: 2 ms

For Rectangular Pulses:

+=

PW

chronaxierheobaseIThreshold 1

� Energy for stimulation.

� Applied Stimulation, usually twice the threshold.

APPLICATIONS OF ELECTRICAL STIMULATION

� Function, or Therapy.

� Cardiac Pacing.

� Cardiac Defibrillation.

� Cardiomyoplasty.

� Electroventilation.

� Phrenic Nerve or Diaphragm.

� SCI patients, intractable hiccups, sleep apnea.

� Superior to mechanical Ventilation.

� Diagnostic: ENG, SEP.

� Control of epileptic seizure.

� Vagus nerve. Little cognitive side-effects.

� Control of parkinsonian tremor (DBS).

� Gastric Pacing (for Gastroparesis).

� Restoration of lost sight.

� Retina (in RP), visual cortex (optical nerve damage)

� Restoration of lost hearing.

� Cochlear Implants:

� Stimulation of ganglion cells, bypassing hair cells.

� Restoration of neuromuscular function� Restoration of neuromuscular function

� FES, FNS.

� Skin-surface or Implanted.

� Foot drop, Standing or Sitting, Hand function.

� Electrical Muscle Stimulation

� Strengthen muscle.

� Relaxation of muscle spasm.

� Muscle reeducation.

� Increase local blood circulation.

� Electro-Convulsive Therapy.

� Major depression.

TYPICAL STIMULUS WAVEFORMS

� True monophasic.

� Seldom.

� Poisoning by metallic ions.

� Electrolysis.

� Asymmetric Biphasic.

TYPICAL STIMULUS WAVEFORMS

� Symmetric Biphasic

� Charge balanced.

� Asymmetric Biphasic.

� Charge balanced.

TYPICAL STIMULUS WAVEFORMS

� Capacitive Discharging:

� Impulse transformer

� To increase the output voltage.

CAPACITIVE DISCHARGE STIMULATORS

� Use of a Tank Capacitor.

� Capacitor-coupled stimulator.

� Low impedance output stage.

CURRENT-SOURCE STIMULATORS

� Transistor Based.

� Opamp Based.

� Voltage-to-Current Converter.

� Float load.

� V/C Converter.

� Howland Current Source.

� Necessary Condition:

1

2

3

4

R

R

R

R=

� Modified Howland Current Source.

� Improved compliance.

EXAMPLE STIMULATOR� Delivers up to 1mA to a load of 10kOhm.

EXAMPLE

� Opamp Bridge Stimulator

� Master and Slave opamps.

VAN DEN HONERT PATENT

� Problem in multi-channel stimulation.

� Use of independent channels.

IMPLANTED ELECTRODES

).بار خالص تزريق شده، صفر(تحريك دوفازي �

.فرايند تزريق جريان در هر فاز بايد قابل برگشت باشد�

.حل شدن فلز�

.اكسيد شدن مواد ارگانيك و سالين�

.توليد گاز، مواد اسيدي يا بازي: الكتروليز� .توليد گاز، مواد اسيدي يا بازي: الكتروليز�

.ولت 0/8: ولتاژ الزم براي شروع الكتروليز�

.اهميت مقدار خازن اتصال الكترود بافت�

.ميلي كولون بر سانتيمتر مربع براي شروع الكتروليز 0/5: پالتين�

.مواد حل شده در بافت سمي است�

.ميلي كولون بر سانتيمتر مربع براي شروع حل شدن شديد 0/04: فوالد�

:خصوصيت الزم براي الكترودهاي نصب شونده�

.ميكرومتر 100قطر بافت فيبروز، كمتر از : سازگار با بدن�

.بافت بزرگ باشد-خازن پيوند الكترود� .بافت بزرگ باشد-خازن پيوند الكترود�

.امپدانس، خيلي كمتر از فوالد و تنگستن: ايريديوم و آلياژهاي آن�

.استفاده از اليه اكسيد، روي الكترود�

.بافت- عملكرد براساس شارژ و دشارژ خازن اتصال الكترود�

.توسط خود الكترود DCبلوك شدن جريان هاي �

.TiN: نيتريد تيتانيوم� .TiN: نيتريد تيتانيوم�

.IROX: اكسيد ايريديوم�

.فرايند اكسيد و احيا در محل اكسيد ايريدويم�

.ميلي كولون بر سانتيمتر مربع 10امكان تزريق �

NEUROMUSCULAR ELECTRICAL STIMULATION

� Functional.

� Therapeutic.

� Diagnostic.

� Direct: activation of moto-neurons.� Direct: activation of moto-neurons.

� Indirect: Reflex recruitment.

� FDA Class II.

� IEC-60601-2-10: Particular requirments for the safey of nerve and

muscle stimulators.

EXAMPLE CIRCUIT

� Output stage.

� Control circuit.

TENS

� Symptomatic treatment of acute or chronic pain.

� When the source of pain is known,

� and can not be treated.

� Success Rate:Success Rate:

� Initial relief of pain in 70% of patients.

� 25% after a few months.

� Mechanism:� Gate Control Theory.

� Endorphin Release Theory.

� Descending inhibitory pathway theory.

TENS (continued)

� Conventional TENS.

� Normal: 40-150Hz, 10-30mA.

� Low Frequency: 1-10Hz, Close to tolerance limit.

� Uncomfortable.

� Increase the time of analgesia after therapy.

� Burst TENS.� Burst TENS.

� Low intensity stimuli in high frequency bursts.

� Bursts of 5-10 pulses at a rate of 100Hz.

� Each burst sensed as a single pulse.

� Ramped modulation.

� More convenient.

� Rate modulation: Better results by avoiding nerve adaptation.

� Percutaneous Electrical Nerve Stimulation.

� Electro-acupuncture.

EXAMPLE CIRCUIT

INTERFERENTIAL STIMULATION

� Stimulation of deep tissue.

� Applications:

� Acute pain:80-150Hz.

� Edema:1-10Hz.

� Muscle rehabilitation:1-150HzMuscle rehabilitation:1-150Hz

� Up to 150V, 100mA

� Targeting:

� Exact frequency difference.

� Phase difference.

� Use of DDS.

� More power consumption, more electrodes.

EXAMPLE

DESIGN� Using PC sound card.

� Beatinbrain freeware.

� MATLAB programming: ‘sound’ command.

10W Audio Amp

Bridge Config.: 4 times power

� Safety:

� High power.

� Continuous current injection.

� Electrode impedance monitoring.� Electrode impedance monitoring.

� Electrotherapy gel, to prevent burn.

CAUTION IN ELECTRICAL STIMULATION

� Cardiac demand pacemakers.

� Implanted devices, and metal implants.

� Avoid eyes, carotid sinus: hypotension.

� Avoid back neck: laryngospasm.

� Pregnancy.� Pregnancy.

� Avoid head: induce seizure.