Electromagnetic Compatibility And Medical Devices

Have you heard about the wheelchair that moved on its own every time a police car passed by No, it's not part of a joke. This actually happened, and several people were seriously injured when radio signals from the two-way communications equipment on emergency vehicles and boats, CB, and amateur radios interfered with proper operation of the control circuitry of powered wheelchairs, sending some off curbs and piers. Similar reports of improper operation of apnea monitors, anesthetic gas...

Vc

You can use the following Matlab command to look at the actual frequency shift and distortion of the VCO signal sampled through the sound card specgram(y 512 Fs kaiser(2 56 5),220) If you are not a Matlab user, here is how you can write a program to determine the instantaneous frequency (or phase) of the sampled VCO output 1. Transform the incoming signal to a complex data stream using a Hilbert transform.3 This gives I (in-phase) and Q (quadrature-phase) data. A true Hilbert transform is...

Concluding Remarks

There is much more to the design of active implantable medical devices (implants that rely for their functioning on a source of electrical energy or any source of power other than that generated directly by the human body or by gravity) than the short explanations and demonstrations presented in this chapter. The European Union has published a directive that regulates the level of performance and testing applicable to active implantable medical devices. This standard is EN-45502-1, Active...

Lowpolarization Surface Electrodes

Silver (Ag) is a good choice for metallic skin-surface electrodes because silver forms a slightly soluble salt, silver chloride (AgCl), which quickly saturates and comes to equilibrium. A cup-shaped electrode provides enough volume to contain an electrolyte, including chlorine ions. In these electrodes, the skin never touches the electrode material directly. Rather, the interface is through an ionic solution. One simple method to fabricate Ag AgCl electrodes is to use electrolysis to chloride a...

Standards For Protection Against Electrical Shock

It has been a long time now that medical electronic devices left the realm of experimentation and were transformed into irreplaceable tools of modern medicine. This widespread use of a very diverse variety of electronic devices compelled countries to impose regulations that ensure their efficacy and safety. In the United States, the Food and Drug Administration (FDA) is responsible for the regulation of medical devices. In the European Union (EU), a series of directives establishes the...

Direct Stimulation Of Nerve And Muscle

Implantable cardiac pacemakers have been around since the late 1950s. More recently, the same basic techniques have been applied to stimulate the vagus nerve for the control of epilepsy, to stimulate the sacral roots to control the bladder and correct erectile dysfunction, and to stimulate nerves in the spine for the control of pain and angina. In addition, interest in functional electrical stimulation (FES) has grown rapidly during recent years, due primarily to progress made in miniaturized...

Info

Sinusoidal with a frequency of 10 Hz. In a perfect system, this signal would not appear in the PSD because it falls between two discrete frequency channels, much as a picket fence allows us to see details in the scene behind it only if they happen to fall within a slot between the boards. In reality, however, because the FFT produces slightly overlapping bins of finite bandwidth, components with frequencies that fall between the theoretical discrete lines are distributed among adjacent bins,...

About The Authors

David Prutchi is Vice President of Engineering at Impulse Dynamics, where he is responsible for the development of implantable devices intended to treat congestive heart failure, obesity, and diabetes. His prior experience includes the development of Sulzer-Intermedics' next-generation cardiac pacemaker, as well as a number of other industrial and academic positions conducting biomedical R& D and developing medical electronic instrumentation. David Prutchi holds a Ph.D. in biomedical...

Design Of Safe Medical Device Prototypes

Military downsizing, government cutbacks, and corporate reengineering had the opposite effect on the medical industry as they did on all other areas of technology. As R& D budgets shrank, early-generation technologies that had long been considered obsolete for space, security, and military applications suddenly found a thriving environment in the development of new medical devices. For example, cruise-missile tracking technology has been adapted to steer powerful x-ray beams to destroy brain...

Extracellular Stimulation

In clinical practice, the stimulation methods used to elucidate the electrical properties of excitable cells are simply not suitable. To start with, clinically useful stimulation requires stimulating much more than a single nerve or muscle cell, making it impractical to build electrode arrays that can impale a large number of cells simultaneously. Next, even if a sufficient number of cells could be impaled with microelectrodes, it is next to impossible to keep them in place in a living, moving...

Stimulation Of Excitable Tissues

An electrically excitable cell in its resting state is essentially a charged capacitor. The cell membrane is the dielectric, the ionic solutions on either side of the membrane constitute the plates, and differences in the concentrations of ions on each side generate a potential difference of about -70 to -90mV (measured inside the cell against a reference in the extracellular fluid). To generate an action potential, the membrane capacitance must be discharged by about 15 mV in a small region....

Sampling Rate And The Nyquist Theorem

Without doubt you have heard that according to the Nyquist theorem, a signal should be sampled at twice its frequency. Yes, and no. There is no data acquisition concept that is more quoted and less well understood than the Nyquist theorem. Let's explore what this theorem actually implies for proper data acquisition. Nyquist stated that any bandwidth-limited signal can be reconstructed from its digitized equivalent if the sample rate is at least twice the highest-frequency component. Signal...

Pdn

Figure 6.16 The linear power supply for the arb requires a 12 V ac input to produce +5 V for the logic circuitry, 5 V for the ECL logic of the high-speed DACs, and 12 V for the analog circuitry. The same circuit can be used for powering the DDS generator. Finally, a word of caution when building this arb. High-frequency clocks and signals demand proper layout techniques Prutchi, 1994 . Preferably, use a multiple-layer printed circuit board. Separate the analog ground from the digital ground and...

Very Realistic Physiological Signal Sources

No physical model can really replace the biological realism that can be achieved with an intact animal model with implanted instrumentation. However, the intact animal presents the problem that body geometry and exact organ configuration are very difficult to integrate as part of an experimental study. A compromise solution is to use an isolated preparation of the organ generating the biopotentials placed in a synthetic volume conductor that simulates the human cavity holding the organ. Figure...

Ecg Amplifier With Pacemaker Pulse Detection And Artifact Rejection

Patients with cardiac pacemakers may have difficulties, especially just after implantation of the pacemaker and lead system, from failure of the pacing system to properly sense the heart's intrinsic signals or to evoke heartbeats (capture the myocardium). This may reflect problems in the electronics, the leads, the placement of the leads, or the myocardium itself. The most catastrophic event is failure of the pacemaker to capture the heart when the patient's intrinsic rate is slow or...

Output Voltage Into Tissue

Figure 8.12 This circuit generates pacing pulses with an amplitude of 3 or 6 V, depending on the state of the pacing amplitude selector switch. When inactive, microcontroller sets the HIGH AMPLITUDE PACING line low, charging tank capacitor C2 to VDD. To generate a 6-V pacing pulse, HIGH AMPLITUDE PACING line is set low to connect the positive terminal C2 to the battery's negative terminal. For 3-V pacing, HIGH AMPLITUDE PACING is set high, to connect the positive terminal of C2 to VDD. A pacing...

Irf9530

Figure 8.37 An isolated dc dc rated at 3 kV with a maximum 60-Hz leakage of a 2- a A converter powers the battery charger circuitry. A single-chip gel-cell charge controller IC (UC3906) charges two sealed 12-V batteries. Q4 switches power to the high-voltage power supply from the +24-V battery. This switch is tumed-on by Q5 upon receipt of the appropriate command from the shock-box microcontroller. IC9 produces 5 V to run the microcontroller and associated logic. Figure 8.37 An isolated dc dc...

Clinical Uses Of Electrical Stimulation

Clinical electrical stimulation is simply the application of electrical currents to a body, be it for function or therapy. As we just discussed, the current of electrons passing through the wires is converted into a current of ions moved within the tissue, which are in turn capable of transporting electrical charge across the membranes of excitable tissues. The purpose of these applied currents is to cause the targeted depolarization of nerve and or muscle to threshold. The most common clinical...

Electrode 2

Interferential Frequency Circuit

Figure 7.19 Circuit of a battery-powered, two-channel TENS unit. IC1 produces a pulse every time the stimulation channels need to be triggered. The trigger frequency can be varied between 3 and 100 Hz. Burst TENS is activated when SW2 connects the reset line of timer IC3 periodically to inhibit IC1 from oscillating. Modulated TENS is enabled by closing SW3, which allows a triangle wave generated by IC2 to modulate the frequency of IC1. The electrodes are driven by step-up transformer Tl....

Intracardiac Impedance Sensor

Impedance sensors for use as hemodynamic sensors in implantable pacemakers don't need to be as accurate as those used for the generation of PV loops. Relative rather than absolute indications of volumes are usually sufficient. As such, impedance sensors used in pacemakers often make certain assumptions that simplify the volume-estimation problem at the expense of precision. The circuit represented in Figure 8.22 is a simple, yet highly effective impedance sensor suitable for implantable cardiac...