Follow the steps below to eliminate or reduce electrical 50 or 60 cycle noise from EMG, NCV, or EP recordings.

1. Replace all electrodes including the ground electrode. Electrode lead wires can break internally and can go unnoticed by the user.
2. Improve electrode impedance values.  Press the “Imped” button on the Wave base.  Click the “Z” button on the Summit display.  Electrode values should be read below 100K.  Improving impedance values will result in signal quality improvement.  The various techniques to reduce impedance values include:
   • try different electrodes – fresh non-expired electrodes
   • switch to different electrode styles such as non-alligator clip or non-disposable reusable electrodes
   • Improve conductivity by cleaning skin surface with alcohol prep
   • Improve conductivity by applying a small amount of conductive cream or gel between the electrode surface and the patient’s skin
3. Turn OFF and/or un-plug possible sources of noise within the exam room.
   • Fluorescent lights.
   • Other equipment in the room such as non-EMG workstations, heat lamps, printers, microwaves, etc.
   • Un-plug laptops not used for testing.
   • If the exam table is motorized, un-plug it.
   • If the exam table is made of metal, ground the table to the ground connector on the back of the instrument.
     

     (EMG electrical artifact identification)

      

4. Move the Amplifier away from the machine, noise from the monitor and keyboard can be picked up by the electrode lead wires.  Move it at least 2-3 ft to the side of the machine.  If the amplifier is mounted on the arm, remove it from the arm and try setting it next to the patient   Also, do not place the amplifier close to power cords or power outlets.  Do not run the amplifier cable close to the power cord.
5. For NCV studies, twist the active and reference lead wires together (i.e., braid them).  By doing this, both electrodes will pick up the same amount of noise which can then be eliminated by the differential amplifier.  (A Differential amplifier amplifies the voltage difference between the active and reference electrodes; if they both “see” the same amount of noise then it will not be amplified)
6. If the instrument is sitting on a metal cart, verify that the cart is grounded to the ground pin on the back of the instrument.  (would be a wire going from a screw on the cart to the back of the instrument)
7. If the instrument uses a Laptop computer; make sure the Laptop is connected to the ground pin on the back of the base unit.  A black wire and crocodile clip is provided for this purpose.
8. Make sure the instrument is plugged into a grounded outlet (three connector).  If the instrument is plugged into a power strip, unplug it and try connecting it straight to the wall outlet.
9. In EMG mode, try using the 60Hz notch filter.  Note: It is recommended to avoid using the notch filter for NCV studies as it will attenuate the motor responses.
10. Try using shielded disk electrodes for NCV and shielded EMG needles (like a Concentric needle or shielded Monopolar Needle).
11. Try moving the Ground electrode proximally on the limb being tested.  So, for upper limb EMG study – place the ground on the upper arm.  For lower limb EMG study – place the ground on the hip.  Any interference ‘riding’ on the patient will have to pass the ground electrode before getting to the needle.
12. If you have a two channel amplifier, turn off channel 1 and try using channel 2.  This will rule out a problem with channel one in the amplifier. (remember to move your electrodes to channel 2)
13. Try moving the instrument into a different room in your facility.
14. Refer to your EMG system help file for base grounding instructions.