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inverse problems in eeg and ecg

what is the basic difference between normal ecg/eeg  and why inverse problems are difficult to solve by normal methods
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Avatar universal
Well, an EEG shows brain wave activity, and an ECG (ekg) shows heart muscle activity.  These are two different and separate parts of the body being tested, so a person could have, for example, seizure activity show up on the EEG and yet the heart will be pumping normally on the EKG.  There is nothing unusual for one to be abnormal and one normal.  As for solving a problem that shows up on one of the tests, this is not exactly "difficult," rather the tests are evidence to be taken into consideration along with other evidence to come up with a diagnosis and treatment plan to improve whatever is abnormal in either system, the heart or the brain.  The idea of the two tests being "inverse" is merely a descriptive term, perhaps, and does not mean if the brain waves are abnormal that automatically the heart muscle activity is going to be normal, and vice versa.  It just means that you have a problem in your brain, but not in your heart.  I hope this clarifies whatever it was you wanted to know.  I could be wrong, I'm not expert in interpreting EEG and EKG results; I just know that ordinarily there is no relationship between the two tests.
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1453990 tn?1329231426
EEGs normally filter out ECG signals.  Both EEG and ECG are based on measuring voltage, not current.  They also measure the voltage using a "differential amplifier."  Unlike the voltage in a US home with is 110 v RMS (root mean square) with respect to ground, human bodies have no ground, the the baseline "floats" all over the place.  

The heart signal is 150 milli volts.  The monitoring frequency response of 0.5-40 Hz.  The diagnostic frequency response range of 0.05-100 Hz.

EEG voltages at the skins surface are typically 10-100 micro volts (more than  and the frequencies are listed below:
EEG in to the following frequency bands:

Delta 0.5-4Hz
Theta 4-8Hz
Alpha 8-13Hz
Beta 13-30Hz
Gamma 36-44Hz

Both systems are designed to reject the other signal by measuring electrode-to-electrode and using high pass and low pass filters to reject unwanted signals.  You will notice that the EEG signals are all below the 50-60 Hz poweline frequencies and are easy to "clean up" with a low pass filter.  ECG is a bit harder since the 50-60 Hz frequency range falls right in the middle of the diagnostic frequency response.  In this case, notch filters are used to attenuate the 48-62 Hz frequency range.

Hope that helps,

Bob
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Avatar universal
I should clarify a couple things since your question was directed to the "inverse problem," which, as I said, is a descriptive term, but it has to do with difficulty interpreting where in the brain the signal is coming from, due to the multitude of brain currents picked up by the EEG.  But my first post responded to what I thought was a question about any inverse relationship between an EKG and EEG that differed in some manner.  Also, a heart-type signal CAN come thru the EEG, again this is an interpretation situation, which a monitor for the heart will help distinguish that signal origin from a brain wave.  Used to be, all docs had was monitors.  But since we now have CAT scans and MRIs, we can SEE internal structures in the brain and where, for example, an abnormal signal from an EEG is being picked up, like an abnormal growth might cause an electrical discharge, but not know where it comes from necessarily.  Also, when an EEG is done, as long as a monitor is also on the heart, any signals coming from that organ can be compared to the EEG tape and be interpreted as a non-brain signal.  I'm just telling you this in case you were talking about interpreting "problematic" EEG signals, as to their origin, rather than an inverse relationship between the results of an EEG and EKG, which is what I thought you were asking about originally, as tho you had a good result with one and a bad result with the other.  
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