Highlights

Contents

Technical tools for SFEMG

Trigger

Delay

A few ways to get single muscle fibers in situ in man

Position of loudspeaker, remotely or closely, - GREAT difference.

The birth of Macro EMG

Decrement in paralyzed rabbits, EAMG!!

Konzo

End of course

 

Technical tools for SFEMG

During the development of the SFEMG method, a number of small but often rather useful help tools or “gadgets” as some call them have been developed or at least tested for use in clinical neurophysiology. They may have been more fun than useful, but in some instances survived, even into commercially available equipment.

Trigger

In order to see short duration signals, say 1 ms, that occur with a frequency of 10/sec, i.e. they occupy 1% of the time, it is necessary to use a high display sweep speed, often 02-0.5 ms/div. In more advanced oscilloscopes a trigger was built in, i.e. the sweep started when the signal had reached an amplitude level that could be optionally adjusted. This was not being used in clinical neurophysiology at the time and we could not trigger on the SFAP. It should be noted that the trigger function is present today in all EMG equipment. The default is that all signals with an amplitude exceeding the trigger level start the sweep. We sophisticated the trigger function further by introducing an amplitude window, so that the sweep started as usual when the amplitude was high enough, but was inhibited if the amplitude exceeded another higher amplitude. The amplitude window could be adjusted optionally during the recording. This made it possible to separate signals that had a lower amplitude than the highest (Czekajewski, Ekstedt, Stålberg 1969). This feature has been included in some EMG equipment, but I think that the possibilities it offers have not yet been sufficiently recognized. Another problem was that only signal segments coming after the time of trigger could be displayed on the sweep. This can be seen in some of our early figures. This was solved by using a delay-line, see below.

Delay

The problem with the missing part before the trigger had to be solved. We tried to use a tape recorder with separate recording and reading heads. They are separated by 1-2 cm and by using the correct tape speed; a delayed signal should be obtained. This was not a practical solution - another type of delay line was necessary. Our first solution was to use a one kilometer 14 paired cable. We connected the ends and got a line of 28 km. This gave a delay of 93 µsec, sufficient to see some significant early parts of the signal. This later became an electronic delay with resistors and condensers, and later a digital delay, now the standard in all EMG equipment (Czekajewski, 1969).

A few ways to get single muscle fibers in situ in man

During the development of SFEMG we needed to prove that we were able to record from single muscle fibers. How to achieve this in human?

Fibrillation potentials are usually considered to be generated by individual fibers, so by recordings from such signals we could determine their characteristics – good similarity to our SFEMG signals.

Another trick was to inject intramuscularly a small dose of sodium citrate. This will chelate the sodium ions and fibers start to fire independent of each other. A weak pain is felt.

Theoretically partial curarization should be a method. At the initial stage of neuromuscular block of the voluntary activated signal, individual building blocks (signals from single muscle fibers) can be seen. When the jitter increased individual components in possible compound signal started to show increased jitter and often increased latency. Thus single fiiber action potential (a.p.) revealed themselves as single fiber a.p. With further effect of the curare, these jittering components also show intermittent and then complete block, The all-or-none behavior strongly indicated that the spike was from a single muscle fiber. It is a very short moment when this occurs and therefore this technique never became a practical method to prove single fiber characteristics. Often however, the spiky signal under exploration showed an all-or-none behavior upon curarization, i.e. was present or absent. This was used as a strong indicator of a recording from a single muscle fiber.

Position of loudspeaker, remotely or closely, - GREAT difference.

In 1978 we gave an EMG course in Bombay (Willison-England, Trojaborg -Denmark and me-Sweden). One evening we were kindly invited to Mr Engineer’s for dinner. He had also invited Ravi Shankar, relatively early in his career. All of us, around 30 persons,  were seated on the floor to listen to his music performed on sitar and some other instruments played by Mr Shankar’s companions.  Since the listening group was large and the space quite big, a loudspeaker was placed at the end of the room. Robin Willison was sitting close to this loudspeaker, perhaps 15 m away from the players. A wonderful evening.

 

 

Next morning, Dr Willison had a comment on the sound quality. He hear the muscle both directly, with the normal delay for sound in air 50 msec for the 15 m, and from the loudspeaker, which produced the sound without delay. His ear was very annoyed by this dual, non-simultaneous sound input.

I well remember when they described the trick of using different delays for the sound to loudspeakers in Westminster Abbey; those speakers far away from the pulpit had a longer delay than those placed closer to the pulpit.

The opposite situation occurred in our laboratory. During a visit to us by Dr. Jasper Daube, he pointed out that a problem he had with the EMG they used (at that time a Neuromatic 2000, the same as ours), which gave an annoying time difference between the signal display and the sound could not be detected in our lab.

 

 

Fig showing an EMG equipment (Neuromatic 2000). Internal loudspeakers are muted and separate loudspeakers 3-6 m away are connected.

 

This EMG machine had a technical feature to first record a signal segment for the total display time, say 20msec. Not until after 20 msec was the trace displayed on the screen, while the sound was “on line,” in real time. With a very slow sweep, you could easily note this, but with short sweep times only an expert like Daube could detect this. In our situation, often using a sweep time of 20 msec, we had free standing loudspeakers placed 3-6 m away (different for different rooms) instead of the inbuilt speaker. Therefore the sound was delayed (time through air) by about 10-20 msec, throughout the range of sweep speeds that we used in routine. We should have had a system by which the loudspeakers moved, depending on the sweep speed!

The birth of Macro EMG

Together with Dr. Hilton-Brown, I was visiting Columbus, Ohio in the late 70’ies. We discussed EMG (what else?) while walking on the street. Intrigued by McComas’ relatively new publications on MUNE, we asked if that method could be improved. His method was to use a metal strip as the surface electrode over the muscle, usually small and thin muscles, such as ADM or EDB. Our own studies had shown how motor units deep in a large muscle such as biceps, did not give a signal to a surface electrode. Was there a way to get a large metal electrode inside the muscle, close to the MU? Well, for EMG with concentric needle electrodes (our standard) we always have a large piece of metal inside the muscle – the cannula of the needle. So, on the street in Columbus we decided to use the cannula for recording. Back home we made such recordings with a SFEMG electrode, triggering on the SFEMG action potential and averaging the time-locked cannula signal. We found that the amplitude depended on the depth of the electrode. (By the way, this cannula signal is usually subtracted from the tip-recorded signal in EMG. Since superficial positions of the electrode give larger cannula signals, more will be subtracted in EMG, and a superficial MU will be seen with a lower amplitude. We therefore modified the SFEMG electrode by Teflon insulation except for the distal 15 mm, which gives a large but standardized recording surface as long as the electrode is inserted at least 15 mm. The triggering SFEMG electrode was placed 7.5 mm behind the tip, in the center of the bare part of the cannula. This then became the classic Macro EMG setup.

Decrement in paralyzed rabbits, EAMG!!

Over the years I have experienced in a couple of important and breath-taking moments.

 

One was the decrement and jitter in rabbits that had developed antibodies to ACh-receptor. This was the first clue of postsynaptic receptor involvement in MG (Heilbronn E, Mattsson C, Stålberg E. Immune response in rabbits to a cholinergic receptor protein: possibly a model for myasthenia gravis. Proc 3rd int cong on Muscle Diseases, Newcastle 1974). The report came out just after the report by Lennon VA, Lindstrom JM, Seybold ME. Experimental autoimmune myasthenia: A model of myasthenia gravis in rats and guinea pigs. J Exp Med 1975; 141:1365-1375

Konzo

A memorable moment in my scientific life was when in Oct 1991 we were asked to examine two patients brought to Uppsala from the Congo. They had acute spastic paraparesis and the pathophysiology was unknown. Insufficiently dried cassava had produced cyanide poisoning with irreversible symptoms. They were brought to Uppsala.  For these patients, accompanied by family doctors and some locals, this event must have been a shock. Flying in an airplane, coming to a hospital, instruments giving electric shocks, and the noise in MRI. The hospital staff did its best to understand their situation and help them adapt.

Blood chemistry - normal. Imaging techniques - normal. A full EDX revealed no abnormalities in motor or sensory nerves. EEG was normal in one and of low amplitude in the other patient. But when it came to transcortical magnetic stimulation, we got the clue. No responses from arm or legs. The conclusion was cortical inexcitability in this disease, which was called Konzo. The studies continued and led to Dr Tshalas’ doctoral thesis. Later Dr Karin Eeg-Olofson and eng PO Fällmar from Uppsala went to Zaire for field studies. Local education on the cause was implemented.

End of course

This was the last day of an SFEMG course in Chapel Hill NC, US in 1987 held in an anatomy auditorium.  At the end of my good-bye speech I tripped backwards and banged into the wall behind. This was assembled by swinging segments about 2 m wide. Each segment could rotate around its vertical middle axis. I pushed one segment which rotated 180 degree and I came into a small pitch dark room. At the same time I heard laughter and applause. I had really not said anything funny, but perhaps my exit was funny enough. When I after a short moment return in front of the wall, I saw a skeleton, hanging on the back of the segment, now widely exposed. The course really had a happy end.

 

A most fantastic sortie, when Erik trips

Backwards through a rotating wall section

In the anatomy auditorium, disappears into

Darkness and a skeleton appears