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Transcript
EE 4BD4 Lecture 20 Therapeutic Stimulation 1 2 Weak and Strong Stimulation Recording Amplifier AC Coupled (bad choice) 3 Extracellular Stimulation (at cathode) 4 5 Extracellular Stimulation • Stimulation threshold – minimum strength of stimulus required to excite the membrane • Defined by current pulse amplitude and duration • For unmyelinated nerve fibers and muscle fibers can be anywhere along fiber • For myelinated depolarization only at the Node of Ranvier 6 7 Extracellular Stimulation Clinical Applications • • • • Cardiac Pacing Cardiac defibrillation Functional electrical stimulation (next slide) Diagnostic stimulation for nerve conduction velocities • Innervated or denervated muscle maintenance • Therapeutic brain stimulation (ECT, vagal or direct brain stimulation for Parkinsonism or epilepsy, rTMS – repetitive transcranial magnetic stimulation, tDCS – transcranial direct current stimulation, etc.) • Artificial cochlea and vision prosthesis 8 Functional Electrical Stimulation 9 Stimulator Design • Constant voltage (current determined by electrode and tissue impedance) • Constant current (more modern) • Typical pulse durations are 50 µs to 200 µs (some applications use 1 ms and longer • Cardiac or smooth muscle require these longer durations because membrane gates take longer to depolarize • Implantable constant current stimulators can deliver ma’s with voltages < 10V but should have bipolar shapes to minimize charge buildup and tissue damage. • External stimulators can be monopolar but require higher current amplitude (>10 ma) and voltage output 10 11 12 +15v Rat Muscle Stimulator 5V power Power 5V Isolator isolator PC USB Microcontroller CNTRL 1 High CNTRL 2 High CNTRL 2 Low CNTRL 1 Low To constant current source and H-bridge components To CCS Optocoupler Optocoupler H-bridge Inside the H-bridge Constant current source Inside the constant current source (CCS) From H-Bridge From H-bridge Vin DAC + - From optocoupler Rsense Current through Vin ______ rat = Rsense 13