IEEE TRANSACTIONS ON EDUCATION, VOL. 35, NO. 1, FEBRUARY 1992 57

Inexpensive Physiological Recording Systems of Didactic and Practical Value

Diego A. Botta, Silvio Rossi, Adrian C. Salvatelli, Guillermo H. Valdez, and Max E. Valentinuzzi

Abstract-A recording physiological system using inexpensive elements was designed and built by a group of bioengineering students. Three consecutive stages were developed over a 26-week physiology course period: a) a single-channel mechanical recorder (for myograms), implemented with a long very light wooden dowel and an arrangement of pulleys and levers; b) a two-channel recorder (mechanical and electrical), using an inductive proximity transducer; c) a digital data acquisition and display using an A/D converter, a Commodore 128, and the GRAPHICS 1 software with a joystick. The instrument showed good performance for teaching purposes, generating enthusiasm and motivation in the students.

I. INTRODUCTION T the beginning of the 1987 undergraduate physiology A course (2 terms, 13 weeks each) offered by the Bioengi-

neering School of the Universidad Nacional de Entre Rios, ParanB, Argentina, a special elective project was given to the students with the following objective: “Design and build a simple mechanical movement indicator (or recorder).”

Along with this task, three other objectives were pursued: 1) spur engineering creativity and manual skill; 2) obtain physiological insight by actual animal experimen-

tation; 3) furnish the laboratory with some basic (although rudi-

mentary) house-made equipment. (Facilities available at that time were minimal because the school was still in its organi- zational stage).

Obviously, the basic motivation was to engage the students in a relevant design project.

The recording system was primarily intended for animal experimentation (for example, to study muscle or cardiac elec- trical and/or mechanical activities). In that respect, sensitivities of 10 mV/cm and 1 g/cm were specified as guiding values. The signal-to-noise ratio was tentatively established in the order of 20. Drift was not considered to be a problem.

11. METHODS AND MATERIALS For orientation, the students received a schematic outlining

a possible simple idea to implement the instrument. Further- more, they were left alone and were free to consult and/or try their own ideas. Groups of up to four students each were formed. Every other week or when needed, they consulted with

Manuscript received January 1990; revised September 1990. This paper was presented at the IEEE Engineering Medicine and Biology Society 10th Annual International Conference, New Orleans, LA, November 4-7, 1988.

The authors are with the Laboratorio de Bioingenieria, Universidad Nacional de Tucumln, 4000 Tucumhn, Argentina.

IEEE Log Number 9104604.

the instructor or presented partial results as they advanced in the project. The basic materials were furnished by the students, mostly taken from the home.

At the end of the course, all groups presented the equipment (as in a small science-fair exhibit), offering demonstrations accompanied by oral and written reports, one of which was selected as the basis for this technical description.

Following student initiative, the project was divided into three stages that were developed over 26 weeks:

a) single-channel mechanical recorder; b) electromechanical proximity transducer and recorder; c) digital data acquisition and display. The following section describes the aforementioned three

stages.

111. RESULTS

A. Single-Channel Mechanical Recorder

Conceptually, undertaking this initial stage meant adopting a position similar to that of Carl Ludwig back in 1847, as a kind of historical revival [ l ] of which the students were per- fectly aware. Geddes’ book on blood pressure measurements represents an excellent and fresh exposition [2].

A 40 cm long horizontal light wooden moving arm (MA), attached to a system of levers, wheels, and springs on one end and provided with a writing pen on the other, was affixed to a board. The writing end lightly touched on a paper roll driven by a small dc battery-operated motor (from an old electric calculator) (Figs. 1 and 2).

Frog ventricular contractions of more than 2 cm amplitude (on paper) were recorded clearly showing, during vagal block- ades, smaller atrial and sinus venosus contractions (Fig. 3). Paper speed was known and, thus, time marks could be drawn.

B. Electromechanical Proximity Transducer and ECG Recorder

A tiny metal foil (MF) was glued to one side of the moving arm which, as it partially rotated due to muscle contractions, got closer to or more distant from an inductance (L), that was part of an electronic oscillator [3] (Fig. 4). Changes in frequency were demodulated, yielding a variable voltage signal that indicated proximity. This signal and the ECG from body electrodes (via an amplifier) were displayed on a dual-channel storage oscilloscope.

C. Digital Data Acquisition and Display

Using A/D conversion (0-5 V, 8 bits, 500 KHz sampling frequency), a Commodore 128, and the GRAPHICS 1 software

0018-9359/92/0200$03.00 0 1992 IEEE

-~ ~- __ ___

58 IEEE TRANSACTlONS ON EDUCATION, VOL. 35, NO. 1, FEBRUARY 1992

Fie. 1. Basic arrangement of the mei mica1 recorder. (a) Si I \ I view. The heart H, within the body of the animal, pulled downward during its contrac- tions via a thread, Th, tied to the apex and threaded through pulleys P1 and P2. The other end of the thread was attached to one side of the moving arm. An elastic band, ECB, counterbalanced the force exerted by the heart. The screw A S allowed adjustment of the tension given to ECB, as needed. (b) Top view. The moving arm, Ald, has 0 as its rotation center. Its writing end rests lightly on the paper placed around the rotating cylinder, RC, driven by a dc motor. Fig. 2 clarifies this schematic.

Fig. 2. Mechanical recorder. A bullfrog (Bufo purucnemis) lies directly under pulley P1. Pulley P2, the elastic band ECB, and the adjustable screw A S are clearly seen. Black boxes on the right contain the electronics, power supply, and batteries necessary for the proximity transducer L and the driving motor.

/"

1s

( b) Fig. 3. Cardiac myograms from Bufo puracnemis. (a) Ventricular contrac- tions, V, during normal sinus rhythm. Frequency: 36/min. (b) Sinoatrial block due to vagal stimulation. The record shows on the left the atrial contraction, A, followed by the bigger ventricular contraction V. Thereafter, a single sinus venosus contraction, SI.', is clearly depicted. The next SI,' contraction is partially hidden by the atrial activity. Notice the change in slope of the atrial contraction, probably due to sinus venosus movement. Ventricular frequency: 16Jmin.

with a joystick, the electrical and mechanical channels were displayed either on the monitor screen or recorded by the printer (Fig. 5).

IV. DISCUSSION Our objectives were met: obtaining an instrument which,

within its limitations, performed the task it was intended for. It was inexpensive because most elements came from home supplies. Above all, the device provided excellent didactic value (in mechanics, electronics, physiology, computing, and even in history of science), generating enthusiasm and mo-

Fig. 4. Inductive proximity transducer. This figure is a closer view of the left-side portion of Fig. 2. The metal foil, M F , was glued on the right side of the moving arm, facing the inductance L.

tivation. Students actively interacted, discussed, searched for information and for elements of different types, and developed an appreciation of the efforthesult relationship.

The general philosophy applied during the course tried to integrate concepts, looking at them from different frames of reference, in line with the ideas presented by Howard E. Morgan [4]: "A physiologist should take an integrative rather than reductionist view, regardless of the technology or level

BO’lTA et al.: PHYSIOLOGICAL RECORDING SYSTEMS 59

[2] L. A. Geddes, The Direct and Indrrect Measurement of Blood Pressure Chicago, I L Year Book Medical Pub., 1970.

131 E. A. Bonfils, W. U. Caballero, and J. Aldonate, “Inductive proximity transducer,” in Proc. IEEE Eng. Med. Biol. Soc. loth Ann. Int. Conj. New Orleans, LA, Nov. 4-7, 1988, p. 1287.

[4] H G. Morgan, “The American physiological society in its centenary year,” Am. J. Phys., pp. E285-E286, 1987.

[5] M. E. Valentinuzzi, “The bioengineering program of the Universidad Nacional de Tucumin (Argentina, 1974-1985): IEEE Eng. Med. B~ol . Mug., vol. 5, pp. 21-25, Sept. 1986.

[6] H. V. Sparks and E. A. Petropoulos, “Departments of physiology in the Third World: The struggle for survival and development,” News m Phys. Scr., vol. 3, pp. 258-261, Dec. 1989.

i i ” ’ I ’

. . . . e . , . . . - LYS V

Fig. 5. Two-channel digitized printer display. Upper channel: surface ECG. The atrial signal P was favored by the electrode location. There is indication of damage Lower channel: myogram obtained from the inductive proximity transducer. An atrioventricular block is clearly seen.

of organization at which a problem is approached.” We think this student project, within its modest and limited scope, successfully met these sensible guiding lines.,

As a by-product, the instruments were left in the physiology laboratory to be used by other groups of students, in itself an excellent example. We should remember the perennial difficulties faced by teaching and research laboratories in Third

Diego A. Botta was born in San Justo, Province of Santa Fe, Argentina, in 1966. He received the tech- nical degree in electromagnetics from the Technical School “Fray Francisco Castafieda.” Currently, he is a fifth-year bioengineering student at the Univer- sidad Nacional de Entre Rios, Paranl, Argentina, where he is also a Student Assistant in physiology.

World countries, as elegantly stated by Sparks and Petropoulos

“Many departments in developing countries are situated in beautiful surroundings: flowering trees, lush vegetation, and the splendor of colorful sunsets. These settings would be conducive to peaceful introspection and serenity [instructors and students alike] if it were not for the urgent necessity to find new means to sustain growth. Is this feasible? Is it possible? We believe it is; however, it will require commitment, consis- tency, and a degree of missionary vision and stamina” [6].

This is precisely the case with the Bioengineering School at the University of Entre Rios (UNER) and with the Laboratory of Bioengineering at the University of Tucumin (UNT), in Argentina. We hope the present paper conveys a message.

PI, PI:

ACKNOWLEDGMENT

The first four authors of this paper were third-year bioengineering students in 1987, during the time that Dr. M. E. Valentinuzzi, from the Laboratorio de Bioingenieria

Silvio Rossi was born in Buenos Aires, Argentina, in 1967. He graduated from the Italian Scientific Lyceum “Cristoforo Colombo” in 1985. Currently, he is a fifth-year bioengineering student at the Engineering School of the Universidad Nacional de Entre Rios, Parana, Argentina, where he has acted as Student Assistant in physiology. He is currently par- ticipating in a project related to some technological problems in pediatrics and neonatology.

Adrian C. Salvatelli was born in San Justo, Province of Santa Fe, Argentina, in 1966. He received the technical degree in electromechanics from the Technical High School “Fray Francisco Castafieda.” Presently, he is a fifth-year bioengineer- ing student at the Engineering School, Universidad Nacional de Entre Rios, Paranl.

(UNT), was in charge of the physiology course offered at the Bioengineering School (UNER) under an exchange agreement between both universities. To collaborate in the course, the following instructors from UNT traveled periodically: E. E. DCcima (neurophysiologist), J. C. Spinelli (bioengineer), E. del Pino (biochemist), A. Coviello (physiologist), S. Gamundi (physiologist), L. Peralata (biochemist), G. Orce (physiologist), I. Ramos (biochemist), and J. Gaete (physician).

Guillermo H. Valdez was born in Villa Angela, Chaco, Argentina, in 1967. He received the tech- nical degree in electromechanics from the National Technical School No 1. Currently, he is a fifth-year bioengineering student at the Universidad Nacional de Entre Rios, Paranl, Argentina.

REFERENCES

[1] C. Ludwig, “Beitrage zur Kenntniss des Einflusses der Respirations- bewegungen auf den Biutlauf im Aortensysteme,” Muller’s Arch Anat., pp. 240-302, 1847. publication.

Max E. Valentinuzzi,photograph and biography not available at the time of