Erik Stålberg

In order to study the electrical field around a dipole, which can be used as a simple model to represent the depolarization in a muscle membrane, we used a water filled tank of the size of a home aquarium. The tank was filled with water. Two small silver coins (10 Swedish öre, available at the time) were glued together and isolated from each other. A current was applied between the coins. A probe was moved along the tank (perpendicular to the direction of the coins) and a voltage profile was obtained as a diphasic signal. In experiments, the distance between the generator and the recording probe was varied. One important finding was the increase in signal amplitude when the recording probe was just under the water surface. This was interpreted as a concentration of currents due to restriction of the volume conductor.

This also happens in the SF recordings. The small surface is surrounded by the isolating Araldite, which relatively speaking is very large. This will increase the amplitude by a factor of 2 compared to a wire recording without a shielding wall. We called this the “Wall effect”.

Double lens for 3D pictures

In attempts to exactly define the 3D dimensional position of the electrode inserted into the muscle we used a double lens adapted to an amateur camera, Retina IIIC. This gave two pictures from slightly different angles. In the picture field we placed a cube constructed from metal with the sides of 10 cm. With a special viewer (or you may manage to adjust your eyes properly) you will see a 3D picture. From these pictures the exact position of the electrode could be estimated, but the method was never used in praxis. This was the principle that had been used by archeologists e.g. to measure the pyramids with cameras at the wings of an aero plane.

Double lens objective and viewer

Sweller and split sweep

During the time of analogue oscilloscopes, one had access to the saw tooth signal (X-axis signal). On a separate channel (dual sweep Tektronix 565) a faster sweep speed could be used starting anywhere along the position of sweep 1 which could be used for different purposes. One was to initiate and amplitude change during the sweep time of channel 2. In this way, separate parts of the signal could be amplified or attenuated depending on situation. With later digital instruments it has been easy to accomplish this and is a routine feature of the different amplifications used e.g. in F-was studies.

Similarly this could be used to give different sections of a trace different time base. This split seep speed has not been implemented in EMG equipment yet.

Fig of Tektronix 565 oscilloscope

Sweller with segments of amplified and attenuated signals

Signals segment with different sweep speed

Singing jittermeter

In an early jittermeter, the running jitter values (calculated on 50 discharges) were transformed to a DC level. A continuous display was then obtained of the jitter during activity.

This DC level was also used to frequency modulate a tone, with a height proportional to the jitter. In other words we could listen to the jitter. We could also set a discriminant level, so that only abnormal jitter values were heard in the loud speaker.

Analogue output from the jittermeter. One division corresponds to jitter values for 50 discharges.

Curare experiment Long term recording

Color coded signals

During the development of the MUP analysis program, it was of interest to detect discharges with a fast rising slope. This was done on-line by calculating the derivative of the signal. A derivate values less than a given value change the color of the displayed signal and it was thus directly see signals with sharp rising phase. This may have application in some types of EMG recordings, not yet implemented.

Remote signal analysis

When I in 1967 moved to the clinical neurophysiology department of the Academic hospital, I still had analysis equipment in my previous lab across the street. To allow analysis of signals from patients from the EMG we had to use the research equipment. Swedish Telecompany made a large, generous and unique effort in digging a 300 m 14 double paired cable under the street with connection of the EMG lab. Fourteen line amplifiers compensated for amplitude loss. In this cable we transferred EMG signals, video, bilateral control signals for the oscilloscopes and sound (a pilot´s throat mike ). This was the first telemedicine transmission of biological signals in Sweden. We used this connection for some years in routine quite successfully until we could afford separate analysis equipment in the EMG lab.

Line amplifier for the long distance transmission

EEG transmission via telephone

In an early attempt (1969) to transmit neurophysiological signals over long distances, we tried a system with telephone transmission. The EEG signal was frequency modulated around a carrier frequency of 1300Hz (optimized for telephone lines). The signal was correspondingly demodulated on the receiver side. We used only one channel. More channels can be used, using separated carrier frequencies. We used this for testing between Uppsala and Gävle also with ECG signals. Multichannel systems on the same principle was then used between hospitals in Göteborg.

	Sent
	Received

Single channel EEG recording transmitted over telephone line from Swedish westcoast (Edshagen) to the Dept Clin Neurophysiology in Uppsala. EEG signals superimpose nicely. Some short artifacts are seen on the received signal.

Throat microphone

The sound system in the telemedicine connection we used a pilot´s throat microphone to suppress sound from the EMG and other surrounding sound. Worked fine but maybe somewhat odd for the patient to see the doctor´s equipment.

Simulation of the electrical field using water capillaries

Multi electrode recordings from one muscle fiber seen with 12 electrode the electrical field can be studied. One analogue method was to place vertical glass capillaries in a scaled pattern exactly like the electrode surfaces in the multi electrode. The glass capillaries were filled with colored water corresponding to the amplitude obtained from the electrodes. In this way an analogue picture was obtained of the electrical field around the electrode.

Detail of the electrode surfaces in the multielectrode used to study signals distribution

Things without photos

Delayline

When triggering a signal on the oscilloscope, segments before the trigger could initially not be seen. We used the speed of electricity (light) along a metal lead (speed of light) to obtain a delay. A drum (about 1.5 m in diameter) with 1 km of a 14 pair cable was purchased and placed in the lab. The thread ends are connected a so 28 km of cable was obtained. This gave a delay of 93,4 µs, enough for us.

Cooler:

Pharmacological institution did not have air condition. We mounted a cooler of a truck (similar to the one in Fig) in the window and a fan in front to remove some of the heat from all instruments.

Intercom

The lab had two rooms. For communication we used a rubber tube in a hole through the wall, with funnels at both ends. This was also used to send white smoke from Ekstedt´s cigar when we accepted the application of a new engineer (c.f. procedure for new Pope).

Voice control of the EMG equipment

In the 1982, we tried to control some the functions in the EMG equipment (Medelec, MS92) by voice. At that time we used an Apple IIe computer with Cognivox™. Functions such as STIM, CAMERA, START-STOP (TA analysis) were used. The program worked pretty well with short commands. For longer word sequences the detection accuracy was too low to be used in routine (you cannot risk a train of stimuli if you cough!) and also required individual voice calibration. If I had a sore throat, the system denied obeying.

Ratemeter

Sometime it was important to have a given firing rate of the muscle action potentials. With electrical stimulation this was directly obtained, but with woluntary activation we had to give the patient a good feeed back. An early method was to use a tachometer from a car to which the trig pulses corresponding to the triggered sweep were fed. Now the patient could learn to keep a pretty constant rate with with the range of 7Hz-30Hz.

Digital tape analysis

When we purchased an incremental digital 8 channel tape recorder, we also made sure that we could detect possible data errors. A small box with magnetic properties made the job, bit by bit. The tape was place over a magnetic area and the “0” and “1” digits became visible!

Combined Multi- and Thermo-electrode

To study the effect of temperature on propagation velocity we used a multielectrode with an inbuilt thermoprobe. (for other electrodes see separate “Electro-tek”)

Measuring time with voltage, The “WOBBLER”

In the 60-ties, before we had a time interval counter, we had to measure time by other means. One trick that could be used to measure time between two parallel signals (for propagation velocity across a multielectrode) was to superimpose a sine wave (1KHz) horizontally. The amplitude was adjusted until the sine waves met and a white line was seen. The amplitude was calibrated into µsec. The accuracy was better than 1 µsec.

Low frequency to demonstrate the principle - 1KHz

Some of these things are now Usual, some Museal