What is the H-reflex EMG?
The H reflex is basically an electrophysiologically recorded Achilles muscle stretch reflex. It is performed by stimulating the tibial nerve in the popliteal fossa. Needle EMG is used to assess both nerve and muscle function.
How do you elicit H-reflex?
The procedure to elicit the H-reflex usually involves applying a percutaneous electric stimulus to a mixed nerve. For example, when eliciting the soleus H-reflex, a 1-millisecond square wave pulse is applied to the posterior tibial nerve in the popliteal fossa.
What is the difference between H-reflex and F wave?
F waves can help determine the presence of a polyneuropathy. A waves can reflect axonal damage. H reflexes provide nerve conduction measurements along the entire length of the nerve, demonstrating abnormalities in neuropathies and radiculopathies.
What does abnormal F wave mean?
The F-wave is a compound action potential evoked by supramaximal antidromic stimulation of a motor nerve16). The absence or slowing of F-waves may be an isolated conduction abnormality, especially during the early stages of illness17).
Why do doctors flick your fingernails?
Hoffman’s sign or reflex is a test that doctors use to examine the reflexes of the upper extremities. This test is a quick, equipment-free way to test for the possible existence of spinal cord compression from a lesion on the spinal cord or another underlying nerve condition.
What is the Hoffman’s reflex?
[1] The Hoffman sign is an involuntary flexion movement of the thumb and or index finger when the examiner flicks the fingernail of the middle finger down. The reflexive pathway causes the thumb to flex and adduct quickly.
Why is H-reflex important?
The H reflex is most useful as an adjunct study in the diagnosis of peripheral polyneuropathy or S1 radiculopathy. The H reflex latency and amplitude is the most sensitive, yet nonspecific, among the nerve conduction studies in the early phases of Guillain-Barré syndrome.
What is wave latency?
Analysis. Three examiners independently determined wave V latency for each ABR recording. A different set of three examiners determined latencies in the ears with HL as the data were collected later in time than the NH data. Latency was calculated as the delay between the wave V peak and stimulus onset.
What causes F-waves?
F waves are recorded from muscle after maximal stimulation of its nerve. When a motor nerve axon is stimulated, the action potential propagates in both directions so that an orthodromic potential can be directly recorded in muscle as a CMAP and an antidromic potential conducts proximally to the anterior horn cell.
What is a normal F-wave?
Maximum normal F wave latency for median nerve was 25.7 ms for women and 28.5 ms for men with stimulation at the wrist. It was 23 ms for women and 25 ms for men with stimulation at the elbow. Maximum normal F wave latency for ulnar nerve was 26.45 ms for women and 28.9 ms for men with stimulation at the wrist.
Why do doctors flick your middle finger?
The finger flexor response is demonstrated by a sudden flexing of the thumb and/or index finger. There are two ways to cause this response: The doctor snaps or flicks the nail of the middle or 4th finger. A positive finger flexor response elicited in this manner is known as the Hoffmann reflex or sign.
What is inverted Supinator reflex?
The Inverted Supinator Test is used for identifying a lesion at the C5-C6 spinal cord level. The Inverted Supinator Reflex is a test that was introduced into clinical medicine by Babinski (1910). A hyperactive response of the finger flexor muscles; a response that is subserved by a lower spinal cord segment (C8).
How is the latency of the H reflex determined?
H-reflex latency can be determined easily from charts, according to height and sex or from published normal values. Whatever these values however, the best normal value in localized processes is the patient’s asymptomatic limb. If no facilitation maneuvers are performed, the difference in latency between both sides should not exceed l ms.
How is the amplitude of the H reflex measured?
The H-reflex can be evaluated either through the latency of the response or the reflex size (peak to peak amplitude). While there are established values for the latency of this response (time from stimulus application until initial deflection from baseline), this is not the case for the amplitude.
What does the absence of the H reflex mean?
H-Reflex. Its absence or abnormal latency on one side strongly indicates disease if a local process is suspected. Much controversy remains, however, on whether its absence bilaterally in otherwise asymptomatic individuals is of any clinical significance.
What happens to H reflex at low stimulation?
At low stimulation intensities, Ia afferents are activated first which causes activation of the muscle’s motoneurons eliciting a small amplitude H-reflex. As stimulation intensity further increases, the amplitude of the H-reflex increases which activates alpha motoneurons, and the direct muscle response (M-wave) is now observed.