System and method for measuring bioelectric impedance in the presence of interference
A system for measuring bioelectric impedance in real time, in the presence of interference and noise is disclosed. A small electric current is injected into a biopotential electrode system, and then the measurement is tested for contamination by electrical interference or other noise sources.
1. A system for measuring bioelectric impedance in a biopotential measurement system and determining the validity of said impedance measurement including at least two electrodes, said system comprising:
a first current source for injecting a first current into one of the at least two electrodes;
a second current source for injecting a second current into a second of the at least two electrodes, said second current being equal to said first current and having a polarity opposite said first current;
an instrumentation amplifier having a high input impedance, said amplifier amplifying an impedance signal resulting from said first and second currents; and
a processor for computing an impedance signal to noise ratio and determining the validity of the bioelectric impedance measurement by comparing said impedance signal to noise ratio against an impedance signal to noise ratio threshold value.
2. The system for measuring bioelectric impedance and determining the validity of said impedance measurement of claim 1 further comprising:
an analog to digital converter connected to said instrumentation amplifier for converting said impedance signal from said instrumentation amplifier into a digital impedance signal; and
a clock connected to said first and second current sources and to said analog to digital converter to synchronize the frequency of injection of said first and second currents with a sample rate of said analog to digital converter.
3. A system for measuring bioclectric impedance in a biopotential measurement system and determining the validity of said impedance measurement including at least two electrodes, said system comprising:
a first current source for injecting a first current into one of the at least two electrodes;
a second current source for injecting a second current into a second of the at least two electrodes, said second current being equal to said first current and having a polarity opposite said first current;
an instrumentation amplifier having a high input impedance, said amplifier amplifying an impedance signal resulting from said first and second currents;
a processor for determining if said impedance signal is contaminated by noise;
an analog to digital converter connected to said instrumentation amplifier for converting said impedance signal from said instrumentation amplifier into a digital impedance signal;
a clock connected to said first and second current sources and to said analog to digital converter to synchronize the frequency of injection of said first and second currents with a sample rate of said analog to digital converter;
a first divider for outputting a first pulse train to said first current source and said second current source to cause said first current source and said second current source to generate a current at a selected frequency; and
a second divider for outputting a second pulse train to said analog to digital converter and said processor to cause said processor to operate synchronously with said first current source and said second current source.
4. A system for measuring bioclectric impedance in a biopotential measurement system and determining the validity of said impedance measurement including at least two electrodes, said system comprising:
a first current source for injecting a first current into one of the at least two electrodes;
a second current source for injecting a second current into a second of the at least two electrodes, said second current being equal to said first current and having a polarity opposite said first current;
an instrumentation amplifier having a high input impedance, said amplifier amplifying an impedance signal resulting from said first and second currents; and
a processor for determining if said impedance signal is contaminated by noise, wherein said processor computes an impedance signal to noise ratio, compares said impedance signal to a threshold impedance limit and, if said impedance signal is greater than said threshold impedance limit, compares said impedance signal to noise ratio to a threshold signal to noise ratio to determine if background noise has increased said impedance signal.