Part 1: Components of Medical Instrumentation System Bioamplifier Static and dynamic characteristic of medical instruments. Biosignals and characteristics. Problems encountered with measurements from human beings. Part 2: Organization of cell: Cell Organization Nernst equation for membrane Resting Potential Generation and Propagation of Action Potential, Conduction through nerve to neuromuscular junction.
Bio-Medical Instrumentation Components of Medical Instrumentation System Bioamplifier A Bioamplifier is an electrophysiological device, a variation of the instrumentation amplifier, used to gather and increase the signal integrity of physiologic electrical activity for output to various sources. It may be an independent unit, or integrated into the electrodes Variations of Bioamplifiers Electrocardiography Electrocardiography (ECG or EKG) records the electrical activity of the heart, across the surface of the thorax skin. The signals are detected by electrodes attached to the surface of the skin and recorded by a device external to the body. The amplitude of ECG ranges from 0.3 to 2 mV for the QRS complex, which is used to determine the interbeat interval from which the frequency is derived. Electromyography: Electromyography (EMG) records the electrical activity produced by skeletal muscles. It records various types of muscle signals from simple relaxation by using placing electrodes on the subject's forehead, to complex neuromuscular feedback during stroke rehabilitation. The EMG signals are acquired from the electrodes applied over or nearby the muscles to be monitored. The electrodes delegates signals to the amplifier unit, usually consisting of high performance differential amplifiers. The usual types of the signal of the interest are in the range of 0.1–2000 mV amplitude, Unit 1.1 Components of Medical Instrumentation System 1|Page
Bio-Medical Instrumentation over a bandwidth of about 25–500 Hz. Electroencephalography Electroencephalography (EEG) instrumentation is similar to EMG instrumentation in terms of involving the placement of many surface electrodes on the patient's skin, specifically, on scalp. While EMG acquires the signals from muscles below the skin, EEG attempts to acquire signals on the patient's scalp, generated by brain cells. Simultaneously, EEG records the summed activity of tens of thousands to millions of neurons. As the amplifiers became small enough to integrate with the electrodes, EEG has become to have the potential for long term use as a brain-computer interface, because the electrodes can be kept on the scalp indefinitely. The temporal and spatial resolutions and signal to noise ratios of EEG have always lagged behind those of comparable intracortical devices, but it has the advantage of not requiring surgery. High performance differential amplifiers are used for amplification. Signals of interest are in the range of 10 µV to 100 µV, over the frequency range of 1–50 Hz. Similar to EMG amplifiers, EEG benefits from the usage of integrated circuit. The chances of EEG is also mainly from the asymmetrical placement of electrodes, which leads to increased noise or offset. Galvanic skin response Galvanic skin response is a measurement of the electrical conductance of the skin, which is directly influenced by how much the skin is moist. Since the sweat glands are controlled by the sympathetic nervous system, the skin conductance is crucial in measuring the psychological or physiological arousal. The arousal and the eccrine sweat gland activity are clinically found to have direct relation. High skin conductance due to sweating can be used to predict that the subject is in a highly aroused state, either psychologically or physiologically, or both. Galvanic skin response can be measured either as resistance, called skin resistance activity (SRA) or skin conductance activity (SCA), which is a reciprocal of SRA. Both SRA and SCA include two types of responses: the average level and the short-term phasic response. Most modern instruments measure conductance, although they both can be displayed with the conversion made in circuitry or software. Other: Electrocorticography (ECoG) records the cumulative activity of hundreds to thousands of neurons with a sheet of electrodes placed directly on the surface of the brain. In addition to requiring surgery and having low resolution, the ECoG device is wired, meaning the scalp Unit 1.1 Components of Medical Instrumentation System 2|Page
Bio-Medical Instrumentation cannot be completely closed, increasing the risk of infection. However, researchers investigating ECoG claim that the grid "possesses characteristics suitable for long term implantation". The Neurotrophic Electrode (NE) is a wireless device that transmits its signals transcutaneously. In addition, it has demonstrated longevity of over four years in a human patient, because every component is completely biocompatible. It is limited in the amount of information it can provide, however, because the electronics it uses to transmit its signal (based around differential amplifiers) require so much space on the scalp that only four can fit on a human skull. Characteristics of medical instruments Static characteristics describe the performance of instruments for dc or very low frequency inputs. The properties of the output for a wide range of constant inputs demonstrate the quality of the measurement, including nonlinear and statistical effects. Some sensors and instruments, such as piezoelectric devices, respond only to time-varying inputs and have no static characteristics. Dynamic characteristics require the use of differential and/or integral equations to describe the quality of the measurements. Although dynamic characteristics usually depend on static characteristics, the nonlinearities and statistical variability are usually ignored for dynamic inputs, because the differential equations become difficult to solve. Complete characteristics are approximated by the sum of static and dynamic characteristics. This necessary oversimplification is frequently responsible for differences between real and ideal instrument performance. Here we will talk regarding the static characteristics of a Biomedical Instrument. 1. Accuracy: The accuracy of a single measured quantity is the difference between the true value and the measured value divided by the true value. Accuracy is a measure of the total error without regard to the type or source of the error. The possibility that the measurement is low and that it is high are assumed to be equal. 2. Precision: The precision of a measurement expresses the number of distinguishable alternatives from which a given result is selected. For example, a meter that displays a reading of 2.434 V is more precise than one that displays a reading of 2.43 V. High-precision measurements do not imply high accuracy, however, because precision makes no comparison to the true value. 3. Resolution: The smallest incremental quantity that can be measured with certainty is the resolution. If the measured quantity starts from zero, the term threshold is synonymous with resolution. Resolution expresses the degree to which nearly equal values of a quantity can be discriminated. 4. Reproducibility: The ability of an instrument to give the same output for equal inputs applied over some period of time is called reproducibility or repeatability. Reproducibility does not imply accuracy. Unit 1.1 Components of Medical Instrumentation System 3|Page