Late Responses Flashcards
What is the usual F response latency for the median and ulnar nerves stimulated at the wrist? What about in the peroneal or tibial nerves?
25-32 ms;
45-56 ms
What is normal F waves persistence? What is the exception?
80-100%, and at least above 50%:
fibular
What is normal F wave chronodispersion in the UE? In the LE?
4 ms;
6 ms
What percent of muscle fibers does the F response represent?
1-5%
For F response, what is the gain? Sweep speed? Stimulation frequency? How many should be done?
200 microvolts; 5-10 ms; 0.5 Hz; at least 10 stimulations
What maneuver can be performed to “prime” the AHC for the F response?
Jendrassik (make fist in contralateral hand or clench teeth prior to each stim)
What 3 factors have to be taken into account when evaluating a prolonged F response?
- Distal motor latency 2. Conduction velocity 3. Height of the patient
What is a consequence of a motor nerve with an absent CMAP with regards to the F response?
The F response won’t be present
For H reflex, what is the gain? Sweep speed? Stimulus duration? Stimulation frequency?
200-500 uV; 10 ms; 1 ms; .5 Hz (numbers either at or slightly increased from F wave)
What is the normal H reflex latency? What difference in latency between the two sides is significant?
25-34 ms;
1.5 ms
What happens with increased stimulus intensity with regards to the H reflex? What waves also appears?
With steadily increasing current, the H reflex will decline as the M wave increases
What does an increased H/M ratio signify?
Potentially UMN lesions
What is constant in the axon reflex?
Latency and configuration
When are axon reflexes typically seen?
Reinnervated nerves typically after axonal loss lesions, especially with submaximal stimulus
