Chapter 13-Webster Therapeutic and Prosthetic Devices Note: Some of the figures in this presentation have been taken from reliable websites in the internet

Medical Instrument Diagnostic Instrument : Sense various physiological signals, carry out some processing of these signals, and display or record them. Therapeutic and prosthetic Instruments: Electrically stimulate different part of the body to relief pain, cure from diseases, or replace damaged biological organ in the body. Examples of Therapeutic and prosthetic devices: Cardiac Pacemakers Ventilators Heart-Lung machines Artificial Kidney Diathermy Devices Electrosurgical Instrument Cochlear Implant Eye Bionic

Cardiac Pacemakers Cardiac Pacemaker: An electric stimulator that produces periodic electric pulses that are conducted to electrode on the surface of the heart, within the hear muscle, or within the cavity of the heart. Two Type of Pacemakers: asynchronous cardiac pacemaker synchronous cardiac pacemaker

Asynchronous Cardiac Pacemakers Power Supply: Lithium iodide Cathode reaction: Li  Li+ + e- Anode reaction at the Anode: I2 + 2e-  2I- Timing Circuit: pulse rate is 70 to 90 pulse per minute Output Circuit: Constant-Voltage Amplitude pulses: 5.0 to 5.5 V with duration of 0.5 to 0.6 msec. Constant-current amplitude pulses: 8 to 10 mA with pulse duration from 1.0 to 1.2 ms. Block diagram of an asynchronous cardiac pacemaker

Lead Wires and Electrodes Figure 13.2 Two of the more commonly applied cardiac pacemaker electrodes (a) Bipolar intraluminal electrode. (b) Intramyocardial electrode.

Synchronous Pacemakers Provide electric stimulus when the cardiac normal rhythm is stopped. Two type of synchronous pacemakers The demand pacemaker (Irregular SA node firing) The atrial-synchronous pacemaker (AV node is not working) Figure 13.3 A demand-type synchronous pacemaker Electrodes serve as a means of both applying the stimulus pulse and detecting the electric signal from spontaneously occurring ventricular contractions that are used to inhibit the pacemaker's timing circuit.

Atrial-Synchronous Pacemaker Figure 13.4 An atrial-synchronous cardiac pacemaker, which detects electric signals corresponding to the contraction of the atria and uses appropriate delays to activate a stimulus pulse to the ventricles.

Rate-Responsive Pacemaker Physiological variables are used to control the pulse rate of the rate-responsive pacemakers Physiological Variable Sensor Right-ventricle blood temperature Thermistor Venous blood oxygen saturation Optical Oximeter Respiratory rate and/or volume Thoracic electric- impedance

Bladder Stimulator Bladder stimulator is used to treat urinary incontinence and other neurological bladder dysfunctions Urinary incontinence: sphincter muscles surrounding the urethra unable to contract. (Unable to hold) Neurologic bladder dysfunctions: Injured neurons can not stimulate the detrusor muscle of the bladder wall to contract. (Unable to void)

Bladder Stimulator Electrodes stimulate the muscles that controls the urethra or the nerves that supply these muscles. Muscle stimuli: pulse duration 0.5 to 5ms at a rate from 20 to 100 pulses/sec. Nerve stimuli: pulse duration 0.1 to 0.4ms Current amplitude =1 mA Figure 13.6 A transcutaneous RF-powered electric stimulator Note that the implanted circuit of this stimulator is entirely passive and that the amplitude of the pulse supplied to the electrodes is dependent on the coupling coefficient between the internal and external coils.

Bladder Stimulator http://www.polystim.polymtl.ca/anglais/urinaire/intrurin.html

Muscle Stimulators Muscle stimulator: Physical thereby of muscle (comma) Functional electric-stimulation (FES): regain function of paralyzed muscle due to neurological injury. regain functions of lower and upper extremities Figure 13.7 A stimulator system for use on stroke patients suffering from gait problems associated with drop foot.

Pain Suppression and Transcutaneous Nerve Stimulation Electric stimulation of tissues is used as a means of suppressing pain. The gate-control theory of pain: Stimulation of certain neurons can have an inhibitory effect on the transmission of pain information from peripheral nerves to the spinal cord. TENS (Transcutaneous Electric Nerve Stimulus) stimulators are similar to the asynchronous pacemaker with skin surface electrodes of different sizes and shapes.

TENS Stimulus Parameters Wide range of stimuli parameters due to lack of information on the mechanism of TENS. -Monophasic rectangular to biphasic spike pulses -Pulses are modulated in terms of amplitude, width, or rate. -Voltage and current range up to 60 V and 50 mA -Pulse rate range from 2 to 200 pulses per second -Pulse width range from 20 to 400 microsec

Cochlear Prosthesis Regain hearing sensation for deaf individuals whose hearing impairment results from dysfunction of the middle and inner ear. Speech processor Stimulus controller Microphone External coil Internal External unit Stimulator circuit Electrode array Implanted unit

Biological Hearing System Cochlear Tympanic Membrane Ossicles Bones Basilar Membrane Inner Hair Cells Sound S(t) NT(t) = Glutamate Oval Window Spiral Ganglion Cells & Cochlear nerve Auditory Pathways & Auditory Cortex

Frequency of Sound (Pitch) Low Frequency High Frequency

Loudness

Spiral Ganglion Cells & Electrical and Biological Hearing System Cochlear Implant Sound S(t) RF Transmitter & Receiver Speech Processor Microphone Electrodes EP(t) Spiral Ganglion Cells & Cochlear nerve Auditory Pathways & Auditory Cortex

Increase channels 1 > 2 > 4 > 8 > 16 > 32 > Original Sound Simulation Increase channels 1 > 2 > 4 > 8 > 16 > 32 > Original Decrease Channels Original > 38 > 16 > 8 > 4 > 2 > 1 Song 4 > 8 > 16 > 32 > Original Music > 4 > 8 > 16 > 32 > Original