Interrupted Direct Current

Basics of IDC

1. Lecture#07

2. Interrupted Direct current (IDC) If continuous unidirectional current is interrupted, it give rise to series of pulses or phases of unidirectional current. Pulse-duration Inter-pulse duration

3. Interrupted Direct Current ON time OFF time Rise time or ON RAMP Decay time or OFF RAMP

4. Duration & Frequency of IDC: The duration and frequency of the impulses can be adjusted. Frequency of the current reduces with increase in the pulse duration. Pulse duration of 100ms will have frequency of 30 cycles/minute. The interval between the impulses should never be shorter duration than the impulses themselves and is usually appreciably longer.

5. Types of IDC Currents produced for therapeutic purposes may have sudden or gradual fall, hence depending on this there are several types, which are as follows: 1) Rectangular 2) Trapezoidal 3) Triangular 4) Saw-tooth 5) Depolarized Rectangular pulses have sudden rise whereas others like trapezoidal, triangular and saw-tooth have gradual rise.

6. Cont… The impulses in which current rises gradually are often termed ‘selective’ Some equipment allows for low-intensity reversed current between the impulses. Here the chances of electrolyte burns are very less. The reverse wave of current between the impulses reduces the chemical formation, and if the quantity of electricity passed in the reversed current is equal to that in the forward one any chemicals formed are neutralized and the danger of burns eliminated.

7. Selection of impulses Rectangular impulse is capable of producing muscle contraction but selective impulse is always satisfactory. A low intensity and gradual rise in current is often best for stimulation of denervated muscle as it brings about satisfactory contraction with less sensory stimulation than with the rectangular impulses. Proper selection of current leads to elimination of unwanted contraction of innervated muscles present in the closed proximity.

8. Effects of IDC ELECTRICAL EXCITABILITY NERVE FIBRE 0.02-1ms Generate Action Potential Longer duration Less Intensity Shorter Duration More Intensity 3. MUSCLE FIBRE Don’t respond to Shorter duration impulses ?? 0.02-1ms Require More intensity 100-1000ms requires less intensity

9. Physiological & Therapeutic Effects of IDC Sensory Stimulation : During the passage of direct currents the patient is aware of a mild tingling or prickling sensation, which may merge into a mild irritation or itching. Hyperaemia : If sufficient current has passed for long enough an erythema of the skin will be evident under both electrodes, and is more marked under the negative (cathode). This erythema is confined to the area of the applied Electrode indicating a capillary hyperaemia , unlike that due to heat in which arteriolar dilatation occurs.

10. Cont… Relief of Pain: Strong sensory stimulation blocks the pain transmission at the level of spinal cord by pain gate theory. The hyperaemia occurring may help to remove the nociceptive substances and thus reducing pain.

11. Cont… Acceleration of Healing: Electrical stimulation by direct current enhances healing process. It has also got effects on healing of superficial and open wounds. Motor nerve stimulation Denervated muscle stimulation

12. IDC used in To re-educate muscle To gain range Facilitate muscle contraction Increase strength Improve circulation

13. Techniques of Treatment Among the several indications of IDC, muscle stimulation is most important one. Here, treatment should be given in such a way that all muscle fibres get stimulated properly. There are several methods to achieve this: 1) Labile Technique: Here one electrode is fixed over the origin of muscle group and other electrode, which is preferably disc or pen electrode is held over the lower end of the muscle belly to be stimulated or is stroke down it. This is known as labile technique. The movement of the electrode ensures proper contraction or stimulation of all the muscle fibres . Also there is less skin irritation by this technique

14. Cont… 2-Group Stimulation: In this technique active electrode is placed over the muscle group to be stimulated (E.g.:- extensor muscles of wrist in case of radial nerve palsy) and large indifferent electrode is placed over convenient site to complete the circuit. This is known as group stimulation technique.

15. Contraindications to electrical stimulation: Metal implants . Strong muscle contraction might cause joint or muscle damage; detachment of a thrombus; spread of infection; and hemorrhage. Stimulation of autonomic nerves might cause altered cardiac rhythm or other autonomic effects. Currents might provoke undesirable metabolic activity in healed tuberculous infections.