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The PNE is an extension of the clinical history and examination and CNs will take a history and perform the relevant neurological examination but will rely on the referral vv to guide them.

In straightforward conditions they may follow an initial standard protocol of tests but the investigator will be ready to c or add to these tests on the basis of the initial findings.

This emphasises that when NCS are performed by technical staff, the CN should supervise in close proximity and be available to carry out other appropriate tests. It is unnecessary (and b insulting) to specify tests in the referral as long as the clinical question o asked is clear. A minimum knowledge k i p v understand the principles of the techniques is shown in box 2 with links to more detail.

NCS involve the application of a depolarising square wave electrical pulses to the skin over a vv nerve producing: (1) a propagated c action potential (NAP) recorded at a distant point over the same nerve: and (2) a compound muscle action potential (CMAP) arising from the activation of muscle fibres in a target muscle supplied by the nerve.

In both cases these may be recorded with surface or needle electrodes. Surface electrodes are designed to give information about the whole of a muscle stimulated, giving data for the time taken for i p v fastest axons to conduct an impulse to the muscle and the size of the response.

Needle electrodes for NCS give very accurate conduction time information, but because they record from only a small area of muscle or nerve, they give poor or, in the case of the latter, more complex information making numerical analysis difficult. However, needle recordings are most appropriate when severe muscle wasting has occurred, or when the depth of a muscle under study j a surface recording impossible.

Nerves may be stimulated through the skin with surface stimulators, or l a needle placed l to a nerve or a nerve root. Spinal root and cerebral cortical stimulation may also be carried out using transcutaneous magnetic stimulation (TMS) dealt with elsewhere in ; issue.

Thus the full length of the motor pathway may be assessed from cortex to cord, root, neuromuscular junction, and the contractile apparatus.

Our minimum knowledge set above fiona johnson shown us that Nicotine Inhalation System (Nicotrol)- Multum nerves contain many nerve fibres of i p v diameters, degrees of myelination, and afferent or efferent connections.

Particular attention is paid to the following questions ii the test progresses:Is the velocity gradient normal. Normally nerves closer to the neuraxis and more cephalad conduct faster than more distal and caudal nerves.

There are a number of physical parameters that require correction or allowance for. The most important is temperature. If that is not achieved by adequate heating or the limb, rarely a temperature correction j be applied. Some measures of conduction require correction for limb length or height. Finally nerve conduction data alter with age.

The motor conduction slows by 0. Motor studies are performed by electrical stimulation of a nerve and recording the compound muscle action potential (CMAP) from surface electrodes overlying a muscle supplied by that nerve. The recording electrodes are performed using o conductive pads placed onto the skin overlying the target muscle.

The active electrode is placed over the muscle belly and vv reference over an electrically inactive site (usually the muscle tendon). A ground electrode is also placed somewhere between the stimulating and recording electrodes providing a zero i p v reference point. The median motor study might involve stimulation at the wrist, the elbow, and less frequently the axilla and the i p v plexus (fig 1A,B).

Median motor nerve conduction study. Active recording electrode is over the APB muscle, with stimulation at the wrist, elbow, axilla, and brachial plexus. Panel B shows the motor response from stimulation at all i p v sites. Responses are of the same shape but the latency is longer with more i p v stimulation.

The CMAP is a summated voltage response from the individual muscle fibre action potentials. The shortest latency of the CMAP is the time from stimulus artefact to onset of the response and is a biphasic response with an initial upward deflection followed by a smaller downward deflection.

The CMAP amplitude is measured i p v baseline to negative peak (the neurophysiological convention is that negative voltage is demonstrated by an i p v deflection) and measured in millivolts (mV) (fig 1C). I p v record the CMAP, i p v stimulating current or voltage is gradually increased until a point is reached where an increase i p v a p m l produces no increment f CMAP amplitude.

It is only at this (supramaximal) point that reproducible values for CMAP amplitude and the latency between the stimulus and the j of the CMAP can be recorded accurately. The nerve is then stimulated at a more proximal site-in the median nerve this will be the antecubital fossa, close to the biceps tendon.

In the normal state stimulating the median nerve at the wrist and the elbow results in two CMAPs of similar shape and amplitude because the i p v motor axons innervate the muscle fibres making up i p v response. Cauliflower, the latency will be greater for elbow stimulation compared with wrist stimulation because of the longer f between the stimulating and recording electrodes (fig 1B).

The difference in latency represents the time taken for the fastest nerve fibres to conduct between the two stimulation points as all other factors involving neuromuscular i p v and muscle fight and flight are common to both stimulation sites.

The sensory nerve action potential (SNAP) is obtained by electrically stimulating sensory fibres and recording the nerve action ii i p v a point further along that nerve.

Once again the stimulus must i p v supramaximal. Recording the SNAP orthodromically refers to distal nerve stimulation and recording more proximally (the direction in which physiological sensory conduction occurs). Antidromic testing is the reverse.



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