SOME THOUGHTS ON THE TEACHING OF INSTRUMENTATION TECHNIQUES AND ELECTRONICS IN MEDICINE

Transcription

1 Brit. J. Anaesth. (1964), 36, 200 SOME THOUGHTS ON THE TEACHING OF INSTRUMENTATION TECHNIQUES AND ELECTRONICS IN MEDICINE BY D. W. HILL Research Department of Anaesthetics, Royal College of Surgeons of England, London The recent series of six papers on "Some fundamentals of Medical Electronics" has attempted deal with some of the more commonly encountered pics in medical electronics. Within this compass, it has not been possible cover all the pics, and much has had be omitted. For example, pulse circuits and a description of stimulars have had be left out. The subject matter of the series evolved from questions put the writer by the staff of the Research Department of Anaesthetics. This interest has eventually led the organization of courses in the Department on instrumentation and electronics. It was thought that others might be interested in the approach adopted. Some seven years ago the Research Department of Anaesthetics was founded in the Royal College of Surgeons. Since it was a completely new department, a major effort had be made develop the various techniques required for the research programme These included a full range of chemical gas analyzers, ph measurement in blood, and electrodes for the estimation of Po 2 and Pco., and general recording techniques for the electrocardiogram, electroencephalogram, blood pressure and respirary waveforms. Visiting anaesthetists expressed considerable interest in these activities, and it was decided that the Department should put on a one-week full-time course in "Measurement in Anaesthesia". This course has now been put on once a year for the past four years. A programme of a typical course is shown in table I. The first lecture on "Principles of Measurement" dealt with random and systematic errors and the use of TABLE I Programme of a typical course in measurement in anaesthesia. TIME MONDAY TUESDAY WEDNESDAY THURSDAY FRIDAY SATURDAY 9.30 Principles of Some pics in Ventilation in measurement blood pressure Po., Pco J medical anaesthesia electronics 9.30 a.m p.m Measurement anaesthetics in the body of gas tensions Physical methods of gas analysis Demonstration Some basic electronic circuits Recording systems Practical exert Uptake and elimination i nitrous oxid< Demonstration Demonstration Demonstration Chemical gas ph in biological anaesthetic gases analyzers fluids and vapours Demonstration Lec'.ure Use of stimul- ars and display cardiac output of action during potentials anaesthesia Electronic measurements Po,, Pco. Resistance gas flow of anaesthetic apparatus 200 ventilation during anaesthesia Carbon dioxide accumulation in anaesthetic circuits

2 TEACHING OF INSTRUMENTATION TECHNIQUES AND ELECTRONICS 201 various types of graph, such as linear and logarithmic plots and exponential curves. Visiting lecturers are asked give specialist lectures, and Dr. Crul, from Nijmegen in Holland, gave the lecture on methods of recording blood pressure. This covered direct and indirect methods, and methods of testing the response of pressure transducers. Similarly, the lecture on the measurement of cardiac output was given by Dr. Payne, then at the Postgraduate Medical School. He has worked extensively in this field. The rest of the lectures were given by members of the scientific staff of the Department. The content of the course changes from year year, so that it may reflect the current research activities of the staff. For example, the sessions on the measurement of anaesthetics in the body, and the use of stimulars, derived from work on the uptake and elimination of volatile anaesthetic agents and the testing of relaxant drugs. Considerable emphasis is placed on the use of modern equipment by the course students. Thus the number on a course is restricted eighteen. They are divided up in six groups of three students, and six instrucrs are available. In the experiment on the use of oxygen and carbon dioxide electrodes, the students draw blood and measure the tensions with an oxygen polarograph and Severinghaus carbon dioxide electrode. In the ventilation experiment they compared a spirometer with a Wright anemometer, Drager Volumeter and various gas meters. They also used an integrating pneumotachograph. In the experiment with carbon dioxide accumulation, a rapid infra-red carbon dioxide analyzer was used, and also the rebreathing method. The afternoon on basic electronics enabled the students become familiar with the idea of using various cathode ray oscilloscopes, and let them see the effect of negative feedback on the performance of an audio-amplifier. During the afternoon on the uptake and elimination of nitrous oxide, they provided volunteer subjects for the working-up trials of a new experimental method. Although the course really takes two weeks out of the Department's normal programme, it does provide a very real stimulus the staff. It is a good thing have sp and explain what one has been doing in clear terms a group of visiting clinicians. On the other hand, the clinicians bring a "breath of fresh air" the work in progress and provide some stimulating comments. The course and the staff had lunch gether each day. Experience shows that, particularly in research, more and more electronic equipment is being used in medical investigations. It would not be out of place repeat a few words of warning on the use of apparatus. The discussion at the end of the post-graduate course on "Electrical Measurements in Anaesthesiology" organized by the Scandinavian Society of Anaesthesiologists brought out the healthy sceptism of clinical anaesthetists wards complicated moniring equipment. It was pointed out that electronics might measure blood pressure and patient's temperature, but it would not tell the clinician the colour of the body all over. Electronic instruments are not in use indicate when a patient is nauseated, wants pass urine, or that a wound is about burst open. It is obvious that instruments of any kind must never be used in such a way as act as a substitute for clinical judgment. The same applies in the natural sciences, where no amount of complicated equipment can substitute for common sense and the careful planning of an experiment. For most routine procedures very little moniring equipment is needed. However, in research, it is often necessary measure a number of variables, and a write-out on a chart or magnetic tape is invaluable. Many docrs express a desire learn sufficient about the techniques of electronic engineering enable them make the best use of their apparatus. There is also the question of communication between a docr and the hospital electronics or physics departments. It is very helpful if the docr understands some of the terms used in electronics if he has authorize expenditure on equipment, or describe the sympms of a fault in an instrument He is also better equipped widistand the onslaught of salesmen! The problem lies in the fact that institutions, such as the technical colleges, offer lengthy courses, usually leading a formal qualification. Most do not aspire be circuit designers, they just want be "educated users". They cannot spare the time for a long course., and often feel rather strange in an engineering environment. Because of the interest shown by the research staff of the Royal College of Surgeons, it was decided run an evening class in practical medical electronics. The experience of

3 202 BRITISH JOURNAL OF ANAESTHESIA the National Institute for Medical Research in London, and the Massachusetts Institute of Technology, suggested that one evening a week for fifteen weeks would be suitable. Each evening consists of an informal lecture, lasting one hour, followed by one and a rnqf hours in the laborary. The lecture pics cover: simple DC circuits; simple AC circuits; thermionic valve amplifiers; semi-conducr diodes and transisrs; recording and display systems; pulse circuits; transducer systems for the measurement of pressure, flow and volume; electrical methods of measuring temperature; and patient safety and the elimination of electrical interference. As many demonstrations as possible are shown. These include: the use of a small Van der Graaf electrostatic generar produce high voltages; the use of a bar magnet and coil with a galvanometer show electromagnetic induction and transformer action; the use of a three-channel oscilloscope show the phase relationships of a threephase supply; the use of a special simple teaching FIG. oscilloscope bring out the functions of the power supply, deflection amplifier and time-base; the display on a cathode ray tube of the current-voltage characteristics of an ordinary semi-conducr diode and a Zener diode; the effect of positive feedback on an amplifier, showing oscillation and "squegging"because of the emphasis on practical work, the number of students per course is limited twelve, with three instrucrs. The course provides some valuable demonstrating practice for the Department's postgraduate physics research students. The aim of the experiments is teach something of the operation of basic circuits, and give confidence in handling the sort of apparatus, such as oscilloscopes, oscillars, valve voltmeters, and bridges, that they will meet in practice. Figure 1 shows an experiment investigate the performance of an audio-amplifier. Not only do the students appreciate the working of a simple two-valve circuit, but they use a valve voltmeter, oscilloscope and signal generar. They see the 1 Apparatus for the investigation of the performance of an audio-amplifier.

4 TEACHING OF INSTRUMENTATION TECHNIQUES AND ELECTRONICS FIG. 2Q5 2 Experimental arrangement for the comparison of two frequencies effect of negative feedback, and can measure the output audio power. Finally, as a uch of light relief, they play a selection of light music through the amplifier from a tape recorder. The oscilloscope tracing clearly shows the production of harmonics in a waveform. Another experiment, compare two frequencies, is shown in figure 2. This introduces the idea of Lissajou's figures and the use of a circular time base and frequency meter. All the time, some of the mystery surrounding electronic instruments is being dispelled. Towards the end of the course, the students use a vibrating reed electrometer as used in some ph and Po2 meters, a frequency modulation tape recording system for recording physiological variables, and set up the amplifier of an electrocardiograph. They measure the effect of electrode resistance and amplifier balance on the rejection ratio. In short, all the experiments are of a very down--earth kind. For example the students measure the char- acteristics of a valve and transisr, and then move on a commercial valve and transisr tester. Similarly they make up their own bridge circuit and then move on a commercial component bridge. In addition anaesthetists, the electronics courses have been attended by workers in medicine, obstetrics, paediatrics, pharmacology and physiology. Each course ends with an "open evening" when students are invited speak about their own work, and the apparatus they use, and if possible bring along some of the instruments they use. The devices shown have included a radio pill for measuring pressures in the bladder, a foetal ekctrocardioscope, a phoelectric recording spirometer, a rat's tail plethysmograph, an implantable cardiac pacemaker, and a thermisr respiration monir. Both the staff and the students derive a considerable benefit from numerous discussions during the course with people working in different fields. Courses have been running for some two

5 204 years, and have attracted people from all over the University. The writer would be pleased hear of any other similar courses which have been organized for workers in the fields of medicine and biology. Some people suggest that it is not possible put on worthwhile courses of an inter-disciplinary nature. This is contrary the experience of the writer. Most medical graduates have had very little instruction in physics, and virtually none in electronics. Exceptions are those men who were in the radar or wireless branches of the armed services, or who are Hi-Fi enthusiasts. However, the lack of technical knowledge is compensated by the maturity of the students. This type of student allows for some research in teaching methods. The writer has tried the use of a "teaching BRITISH JOURNAL OF ANAESTHESIA machine" so that students could help themselves instruction when they had some spare time, say due the cancellation of an operation list Another interesting possibility lies in the use of "takehome" kits. Here the student is provided with a chassis, a set of basic electronic components, transisrs, and a multi-meter. With,such an arrangement (they are available commercially) the student can construct working circuits in his own time. It is stipulated that the course students must be graduates in medicine or biology. On the medical side they have ranged in status from registrar reader and professor. REFERENCE Electrical Measurements in Anaesthesiology (1962). Ada anaesth. scand., Supp. 11, 235. Printed In Great Britain by John Sherrmtt * Son. Park Road. Altrincham