Cleveland Family Study

17.9.2 Impedance and Signal Quality Overview

Impedance defeats the passage of signals into the electrode and, in turn, the recorder. For PSG studies, impedance value is measured in kilohms, or thousandths of an ohm. Later, the manual abbreviation k will be used for kilohms.

For EEG, EOG, and EMG you want to achieve impedance of < 10k. Most important is the balance (difference) between two sets of paired EEG electrodes. For accurate recording the difference in impedance levels between pairs of EEG electrodes should be less than 5k. For ECG impedance of < 30k are acceptable.

When troubleshooting high impedance, first check that the system (all cables) are connected and electrodes are tightly in place. Loose electrodes create excessive impedance.

17.9.2.1 If All Electrodes Register High

During the impedance check, if all electrodes register high (>10 k) remove the ground electrodes (at Cz and the forehead), re-prep the sites and replace the electrodes.

17.9.2.2 If Only Certain Electrodes Register High

1. If impedance of any pair of electrodes (other than ECG) is >10k, or the difference between any pair of electrodes is > 5 k, remove the electrode, re-prep the electrode site and replace the electrode.
2. If, on a second placement, impedance is still high there are two possible problems:
   • The area of the skin identified for sensor placement has an unusually high impedance or
   • The lead wire or sensor is damaged. Therefore, attempt to address both potential problems by choosing an alternative electrode site (e.g., immediately adjacent to previous site or use of one of the alternative sites indicated above), and change lead wires.
3. If impedance is still high on a third attempt do not attempt to re-prep area. Document your activities on the Signal Verification form.