DENERVATED MUSCLE STIMULATION

1. DENERVATED MUSCLE STIMULATION De-enervation can cause: Disorganization. Atrophy. Degeneration. Fibrosis of muscle fibers.

2. De-enervation can cause Degeneration and fibrosis of the motor nerves. Venous stasis. Thickening of arterial walls Distortion and atrophy of capillaries. Increase in fatty tissue.

3. Atrophy Atrophy from de-enervation is affected not only by the absence of muscle contraction, but also by the loss of axonal transported neuro-trophic substances particularly in type II muscles. It is difficult to stimulate the muscle directly; more current amplitude and longer duration is needed.

4. De-enervation can cause Decrease acetylcholinesterase activity. Increase extra-junctional acetyl choline (Ach) sensitivity. Increase muscle fiber membrane resistance. Increased muscle fiber capacitance

5. Responses to successive electrical stimuli It should be noted that, because further stimuli would fall within the absolute refractory period, a nerve fiber can not respond to successive electrical stimuli applied at frequencies greater than 1000 per second even if the stimulus is strong.

6. Responses to successive electrical stimuli Stimuli of adequate intensity occur after the absolute refractory period and within the relative refractory periods may cause a threshold depolarization and an AP.

7. Strength duration curve

8. Strength duration curve Stimuli with adequate intensity and frequencies greater than 1000 per second may cause nerve to depolarize at frequencies different from those of the delivered current, this is known as � stimulus asynchronous depolarization�.

9. The order of nerve recruitment Larger nerve diameters are recruited before smaller ones, because they have more ions per unit length of the axon, resulting in lower resistance to current flow, and a greater ease of depolarization. Fast twitch fibers are recruited before the smaller slow twitch fibers.

10. The order of nerve recruitment The primary factor that determines the order of nerve recruitment in response to electrical stimulation using surface electrodes is: the location of the nerve fiber to the electrodes, Smaller diameter fibers may lie closer to the surface of the skin that is why the feeling of tingling sensation is felt by the patient before large diameter fibers are stimulated.

11. The order of nerve recruitment As the intensity is increased the stimulus spreads to the deeper tissue recruiting more fibers. If the electrodes are placed in area where there are no motor nerve fibers or skeletal muscle fibers, a painful response without a motor response may result.

12. Effects of electric currents Three types of neurophysiological responses are known to occur:- When electric current is applied to innervated tissue (sensory level response). Skeletal muscle contraction (motor level response). Pain (noxious level response).

13. Effect of space between electrodes.

14. Preferred pulse duration responses

15. The duration and extent of re-enervation depend on:  The nature and severity of the nerve injury. The impact and extent of sequelae of denervation. Repair of nerve after denervation (the longer the duration is not likely to result in functional recovery).

16. ES of de-enervated muscles has been shown Decrease the excessive Ach sensitivity of de-enervated muscles. Decrease fibrosis. Improve blood flow in de-enervated muscle. Prevent or slow atrophy. Studies have shown that ES slowed atrophy in type II muscle fibers but increased in type I muscle fibers.

17. ES of de-enervated muscles has been shown Improve the indicators of tension generating ability of de-enervated muscles. Improve the rate of re-enervation and nerve regeneration. Decrease edema and vascular stasis. Maintain flexibility. Avoid further injury.

18. ES of de-enervated muscles However, some authors suggested that the use of ES for treating de-enervated muscle is impractical.

19. Recommended parameters for de-enervated muscles 1- Current type/wave form DC has typically been used in an interrupted manner, mimicking an MPC with very long pulse duration. 2- Pulse (cyclic) duration long cyclic duration pulse duration MPC They are used to counteract the increased impedance and capacitance of denervated muscle fiber membrane, as well as the resting membrane potentials.

20. Recommended parameters for de-enervated muscles 3- Current amplitude It must be as high as tolerable and that is capable of stimulating titanic contraction of the target muscle. If the sensation is intact it will be quiet painful. 4- Frequency Titanic contraction is achieved at a lower frequency in de-enervated muscle. With AC, lower frequencies are more effective because they are more effective because they result in longer cycle durations. There is no frequency when describing DC. 5- On and off time: Since the de-enervated muscle fatigues readily, it is recommended that the on time is 5 to 10 seconds and the off time is 1 minute.

21. Recommended parameters for de-enervated muscles 6- Ramps No particular ramp is recommended for de-enervated muscle; however a ramp of about 5 seconds will allow the patient to be accustomed to the stimulus. 7- electrode configuration: Placement of electrode on the most excitable part of the muscle is not recommended as the muscle is de-enervated. The dispersive electrode may be placed as a remote or over the target muscle or tendon. The cathode should be smaller than the anode in order to maximize charge density at the treatment site while limiting the response at the other electrode.

22. Precautions Over tissue vulnerable to hemorrhage or heamatoma. Over areas of skin irritations, damage or lesions. In thoracic region in skinny patients. Over eyes. Pregnancy. Over cervical area for patients with a history of seizures. -impaired sensations

23. Clinical Applications Put the patient in a comfortable position, according to the nature of his problem to maximize the potential benefits of the treatment. Before placing the electrodes, inspect patient�s skin. Determine the site of the dispersive electrode, and the size of the cathode electrode. Select the treatment parameters settings. During treatment, ask the patient regarding his comfort and unpleasant sensation. When the treatment is completed, remove the electrodes and inspect the skin again. Measure the outcome of the treatment. Document the treatment.

24. Contra indications cardiac pacemaker, carotid sinuses, venous or arterial thrombosis, thrombophlebitis, indwelling phrenic nerve stimulator, indwelling urinary bladder stimulator, During operation of diathermy device.

25. Electrode configuration