Carbon dioxide (CO2) has anesthetic properties and has been reported to depress the F wave of the evoked electromyogram; the F wave is thought to reflect motoneuron excitability. Anesthetics such as isoflurane also depress the F wave. Because CO2 can depress muscle contractile function, as well as spinal cord neurons, it is unclear whether CO2 depresses the F wave via a central or peripheral mechanism. We anesthetized rabbits with isoflurane (1.4%) and prepared for hindlimb bypass (with a membrane oxygenator) whereby the partial pressures of CO2 in the hindlimb muscle and torso could be independently adjusted. The F wave was recorded from the hindlimb plantar muscles when the CO2 was normal to the hindlimb and torso, and when it was increased (to ≈90 mm Hg) in the hindlimb, the torso, or both. Increasing the CO2 to just the hindlimb had no significant effect on the F-wave amplitude, but increasing the CO2 to the torso depressed the F wave to 52% ± 32% of control; adding CO 2 to the hindlimb during torso hypercarbia did not result in any additional depression of the F wave. CO2 depressed the F wave via a central, not peripheral, mechanism, although the precise mechanism is unknown.
|Original language||English (US)|
|Number of pages||6|
|Journal||Anesthesia and Analgesia|
|State||Published - Feb 2005|
ASJC Scopus subject areas
- Anesthesiology and Pain Medicine