Questions and Answers
1. Why is the CFAM3 headbox bigger than the CFAM2 headbox?
There are two reasons. Firstly the increase in channels from two to four takes up more space. Secondly it has to have more input filtering and protection than the CFAM2. The CFAM2 was purely an EEG monitor. However, with the addition of AEPs in the CFAM3, some electrodes may be placed remotely from the head. Consequently defibrillator and other potentials / currents across the amplifier inputs are likely to be larger.
2. My CFAM3/4 will not file data to hard disc.
Most probably your hard disc is nearly full. The CFAM3 is programmed to stop recording to disc before the disc is actually full. This is in order to give hard disc space for other parts of the software to run. Select "Storage" on the start-up menu to see how much recording time is left. If it is not much, for example less than a few days, you need to back-up some data onto your streamer to make room for data on the hard disc. Please ensure that you make two copies in case one gets damaged. Also keep them in different locations. We would recommend that you keep space on your hard disc for at least a week of continuous recording just in case you have to do just that.
3. If a needle electrode has slipped out and I re-insert it then subsequently I get amplifier overloads.
Don’t do this. Use a new sterile needle.
Prior to the appearance of HIV the use of needle recording electrodes was commonplace by EEG Departments, although only for short periods of 20 minutes or so when visiting a ward or ITU.. After use they were cleaned, re-sharpened and re-sterilised, often only being discarded when half their original length. It was noted that, sometimes, it was difficult to record with a particular needle, but a replacement was OK. When EEG machines made the transition from AC coupled to DC coupled input amplifiers (giving better common mode rejection and lower noise) needles became more of a problem. What seemed to happen sometimes was that wax or oils or grease from the the scalp or hair, or from the hands when cleaning the electrode, coated the electrode surface preventing or reducing proper contact, this having most effect at low frequencies. . Cleaning with an alcohol did not remove the coating. The next time the electrode was used, after sterilising, it kept causing amplifier overloads.
However, if an abrasive cleaner was also used, the electrodes functioned properly.
I suspect that the above is related to your problem. Replacing the electrode with a new one should cure it.
You might ask the appropriate official organisation in your country if there is any current advice regarding the re-insertion of a needle recording electrode. Also check if there is any advice concerning the length of recording time for which such needles may be used.
The CFAM manuals mention the desirability of having prominent warning notices if you are using needle electrodes.
4 Would the use of an overhead heater in a cot cause the metal (silver-silver chloride) electrodes to get hot enough to cause a burn?
Most metal items in contact with the skin will get hot under an overhead heater. This may well cause discomfort and is not desirable. If the heater was close enough or strong enough there may be some risk of too high a temperature being reached. It would certainly cause the electrode jelly to dry out quickly and lead to recording problems. Try covering the area of the electrodes with a white cloth to deflect the heat.
5. What are the acceptable limits of muscle interference?
The CFAM machines constantly monitor the level of scalp muscle activity at the recording electrodes. This is because the frequency spectrum of muscle activity overlaps the spectrum of EEG activity, particularly at the higher frequencies. Consequently the muscle trace is plotted so that peaks in it point to corresponding peaks in the beta trace. Small amounts of muscle of the order of 2 to 5 uVpk to pk will have little effect on the EEG whereas 25uV definitely will. This level will also be causing deflections on the amplitude trace. In the ITU there may be little you can do to reduce scalp muscle except seeing if altering the patient's position reduces it. Even with muscle relaxants given during surgery scalp muscle may not be entirely abolished. The important thing is to recognise that it is occurring and not to be fooled into misinterpreting the other measures.
6. If the CFAM3 fails to calibrate properly what should I do?
The most common cause of this is dust on the calibration contacts. Try wiping the contacts gently with a dry non-abrasive cloth. If this does not work and if the apparatus has been subjected to physical shock or vibration there is some possibility of mis-alignment of the calibration contacts. To check this, push down the calibration contact black cover. Then gently lower the headbox onto the calibration pins whilst looking from the front of the machine to check that they are aligned with the electrode connectors. Repeat this looking from the side. If the alignment is correct but contact is still not being made then the headbox guide rail toward the rear of the machine (the one with the locking wheel ) may have slipped upwards. Ask your Medical Physics Dept to contact us for instructions on adjustment in both the latter cases.
7. My CFAM3 keyboard has stopped working. or The start-up says "keyboard error press F1 to continue"
There is a switch on the back of your CFAM3 that enables you to turn off the keyboard to prevent tampering while the equipment is running unattended. Someone has probably knocked this on accidentally when moving the equipment, or forgotten to reset it. If you know how to adjust the system BIOS you can set it not to give the start-up warning if you wish.
8. I cannot get a calibration AEP
Firstly the calibration signal for the AEP requires you to set zero EEG calibration. If you have a 10Hz calibration signal running and, at the same time your pre-sets are set to reject sweeps with potentials exceeding some level under +-50microvolts, then all the sweeps will be rejected and you will not get an average. You can get a not so accurate AEP calibration, with the 100microvolt peak to peak 10Hz EEG calibration signal running, if you set a sweep reject limit above +-50microvolts. If you are looking at short sweep lengths, say 10 to 20ms, in the presence of large rythmic activity, then you might wish to set "detrend before average". Similarly you may wish to set this when using longer sweeps in the presence of large slow waves.
If you have set the system to clamp the input voltage during a stimulus to avoid a stimulus artefact you may also be hiding the calibration pulse.
9. I get a lot of mains interference indicated on the CFAM trace. Will this affect AEPS?
Mains interference can cause problems with computing AEPS if a multiple of the stimulus rate is synchronous either with the mains frequency or a harmonic of it. In this case, in pre-sets, set the stimulus to dither randomly within a mains cycle.
10. Why do you average before the AEP stimulus as well as after it?
In theory the activity before the stimulus should average to zero since it is not correlated to the stimulus. Therefore pre-stimulus activity suggests that your AEP contains energy not related to the stimulus. However life is not so simple because brains are quite good at anticipating stimuli, especially if they occur at a constant rate. You can try to get around this by making the stimuli occur at random intervals.
If the evoked potential is actually quite long but you are only interested in the first part of it and so use a relatively short sweep, by stimulating at a fast constant rate you may well be adding the tail end of the previous stimulus to the result of the current stimulus. You might like to consider this in relation to the faster auditory evoked potentials.
11. Why do you plot amplitude and frequency responses separately?
Because the way we do it, via a specially weighted filter (see under CFM) ensures that, in many cases, the amplitude and frequency distributions are independent variables. You may like to look up the papers by Glaria and Murray 1985, Murray et al 1986 (in our reference list) in which they showed this independently of ourselves.
12. What is the amplitude plot measuring?
It is the log of the modulation envelope of the EEG, after the EEG has passed through a specially weighted filter. Taking the log converts the resulting Rayleigh distribution to a normal distribution. You can see the effect of this normalisation in CFAM amplitude plots where, for most of the time, the mean measurement is half way between the 10th and 90th centiles.
13. On CFAM3c when I press P to copy the screen to an external printer , my HP ink jet does not respond properly.
This is an obsolete function and is removed in current software issues. Please contact us to update your software.
It will print correctly if you set your printer to IBM graphics mode. This was a common mode circa 1989 when parts of this software were originally written. P now prints to the built-in thermal printer
14. Who coined the term Cerebral Function Monitor?
D E Maynard in 1967. The first version of the CFM, built in 2 weeks and before a chart recorder was added some weeks later, was a box with a meter on the front. D E Maynard thought of three possible names and asked P Prior which she preferred. She chose Cerebral Function Monitor. Nowadays the term is used by many different manufacturers.
15. I cannot get an EEG recorder or the monitor to work in a particular neonate cot.
Unfortunately some cots do generate interference, usually as a result of the presence ungrounded metal surfaces. For example Some cots have an ungrounded metal grill over their heater lamps and grounding this will solve the problem - if this is approved by your local safety advisers and the manufacturer. Sometimes itmay be the result of an electrical fault in the cot. Contact your service Department and ask them to investigate. In general CFAMs are more tolerant than conventional EEG recorders.
