This protocol describes how we examine muscle membrane changes in denervated muscles using MVRC, muscle velocity recovery cycles. The main advantage of MVRCs is that it's a fast and simple method for examining muscle membrane properties in vivo without discomfort for the subject. MVRCs may have a potential to be a diagnostic tool in neuromuscular disorders in the future.
However, further studies are necessary to explore this possibility. We expect MRVCs to a valuable resource tool for understanding the pathophysiology behind several neuromuscular disorders and a biomarker for monitoring the disease progress and drug effects. Since there are no risks and only slight discomfort from this examination, we recommend that you practice on healthy subjects before examining patients.
This technique is completely harmless as long as you follow basic instructions. So, remember to clean with alcohol before needle insertion and ensure that there are no contraindications such as hemophilia or blood thinning treatment. To begin, assess the subject's medical histories to ensure that they do not have any previous nervous system disorders other than the disease group that will be investigated.
Inform the subject in detail about the examinations and request to obtain written consent. Inform the subject about the insertion of two needles in a leg muscle and that the muscle fibers will be stimulated with a weak current. Explain that the sensation may feel slightly unpleasant.
Inform the subject that the stimulation can be turned off immediately at any moment during the recording in case of any discomfort. Then, clean the subject's lower leg with alcohol. Insert the stimulating monopolar needle electrode over the anterior tibial muscle.
Insert the recording concentric needle electrode about two centimeters proximal to the stimulating monopolar needle electrode along the muscle fibers and put adhesive surface electrode as the anode one centimeter distal to the monopolar needle. Place a ground electrode distal to the anode. Connect the recording concentric needle and ground electrodes to the preamplifier.
Ask the subject to remain silent and avoid movement during the examination. Zero the output of the stimulator and connect the stimulating electrodes to the stimulator. Maintain the skin temperature between 32 and 36 degrees celsius using a warming lamp.
Start the stimulator and turn on the semi-automated recording software using the muscle excitability recording protocol. Stimulations start at 2.5 milliamps with one hertz. Increase the stimulus intensity manually by hitting the insert key until a response is recorded.
If the potential appears upside down, hit the minus key to invert the muscle action potential. Adjust the stimulating and recording needles if necessary until recording an acceptable response with a stimulus intensity of less than 10 milliamps. The shape of the muscle action potential should be triphasic and stable.
Avoid large twitches of the whole muscle. Muscle twitches of the whole muscle implies that you are stimulating the end plate. In this case, adjust the monopolar needle or reinsert both needle electrodes in a new site.
A magenta horizontal line appears on the screen indicating the width of the action potential. Adjust the position and length of the magenta line by dragging the line with the mouse. The green horizontal line represents the baseline.
Select stimulus response relationship from the main options. Increase stimulus intensity by hitting the insert key to a max of 10 milliamps or tolerable. Click OK to start descending the stimulus response curve.
Click OK when the test stimulus reaches zero. Set the stimulus intensity to level for stable latency. Click OK to return to the main menu.
Select the option 1-2-5 conditioning stims for recovery cycles. Select a protocol from the recovery cycle options. For example, start quick recovery cycle, skip alternate delays.
Make sure the muscle action potential is stable during the recording and that the needle has not moved. The screen changes automatically to main options when the 34 steps have completed. Click on finish recording and click the save data button.
Start the analyzing software program to perform the analysis offline. Select the recording that will analyzed and click on the OK button. Click on load parameters from the files menu.
Select the MANAL9 option for the analysis. Click OK to continue. When a description of the MANAL9 muscle excitability analysis appears, click OK to continue.
If the potential appears upside down, invert the muscle action potential by typing MM-1. Right click the mouse to make the magenta line visible. Set the window to the base of the peak response and with a width corresponding roughly to the width of the action potential at that height.
Track with the mouse to adjust the window. The window determines the latencies within which the height and latency are measured as indicated by the pale blue lines, and the green line indicate the baseline. Click OK to continue.
Click OK to remeasure the latencies and peaks. Click OK to create an RMC file. Ignore most of the options appearing in the create RCC or RMC form.
Click save and exit to continue. After saving the RMC file, the prompt box provides different options. If frequency ramp and/or repetitive stimulation data have been recorded, follow the instructions to analyze these.
Otherwise, select go straight to create MEM file option to create a MEM file. Click OK to continue. Click save and exit to continue.
Click OK to add the RMC data to the MEM file. Click add from input RMC file to add this data to the MEM file, then change the directory to save the composite MEM file. Then, click save and exit to save it.
Click OK to save the remeasured QZD file to allow differentiation from the original QZD file using a pound sign. In this study, 14 patients were compared to 29 healthy subjects. Subject demographics are shown here.
Recordings from a healthy subject and a patient show distinct difference in percentage change in latency. Comparison of patients'MRVCs with healthy subjects'shows that MRRP was prolonged and early supernormality and late supernormality were reduced in patients compared to healthy controls. The most important step in the MVRC recording is correct needle positioning, where you get a stable amplitude with a stimulus intensity less than 10 milliamps.
