© 2005 – FA Davis Electrical Stimulation Techniques

© 2005 – FA Davis Current Flow Electron Flow (shown in red) –Between the generators and electrodes –To and from the generator Ion Flow (shown in yellow) –Occurs within the tissues –Negative ions flow towards the anode and away from the cathode –Positive ions flow towards the cathode and away from the anode

© 2005 – FA Davis Electrodes Purpose –Completes the circuit between the generator and body –Interface between electron and ion flow –Primary site of resistance to current Materials –Metallic (uses sponges) –Silver –Carbon rubber –Self-adhesive

© 2005 – FA Davis Electrode Size Determines the Current Density Equal size –Bipolar arrangement –Approximately equal effects under exach

© 2005 – FA Davis Electrode Arrangements Based on: Current Density Proximity to Each Other Anatomic Location (Stimulation Points)

© 2005 – FA Davis Current Density Bipolar Technique –Equal current densities –Equal effects under each electrode (all other factors being equal) Monopolar Technique –Unequal current densities At least 4:1 difference –Effects are concentrated under the smaller electrode “Active” electrode(s) –No effects under larger electrode “Dispersive” electrode Quadripolar Technique –Two bipolar electrode arrangements –Two independent electrical channels –TENS is a common example “Active”“Dispersive”

© 2005 – FA Davis Electrode Proximity Determines the number of parallel paths The farther apart the electrodes the more parallel paths are formed More current is required to produce effects as the number of paths increases

© 2005 – FA Davis Stimulation Points Motor Points –Superficial location of motor nerve –Predictably located –Motor nerve charts Trigger Points –Localized, hypersensitive muscle spasm –Trigger referred pain –Arise secondary to pathology Acupuncture Points –Areas of skin having decreased electrical resistance –May result in pain reduction Traumatized Areas –Decreased electrical resistance (increased current flow)

© 2005 – FA Davis Path of Least Resistance Ion flow will follow the path of least resistance –Nerves –Blood vessels The current usually does not flow from electrode-to- electrode (the shortest path) The path of least resistance is not necessarily the shortest path

© 2005 – FA Davis Selective Stimulation of Nerves Nerves always depolarize in the same order –Sensory nerves –Motor nerves –Pain nerves –Muscle fiber Based on the cross-sectional diameter –Large-diameter nerves depolarize first Location of the nerve –Superficial nerves depolarize first

© 2005 – FA Davis Phase Duration and Nerve Depolarization Phase duration selectively depolarizes tissues Phase DurationTissue ShortSensory nerves MediumMotor nerves LongPain nerves DCMuscle fiber

© 2005 – FA Davis Adaptations Patients “get used” to the treatment More intense output needed Habituation –Central nervous system –Brain filters out nonmeaningful, repetitive information Accommodation –Peripheral nervous system –Depolarization threshold increases Preventing Adaptation –Vary output (output modulation) to prevent –The longer the current is flowing, the more the current must be modulated.

© 2005 – FA Davis Electrical Stimulation Goals Muscle Contractions [Instructor Note: More detail on these techniques are found in the CH 13 ppt: Treatment Strategies]

© 2005 – FA Davis Motor-level Stimulation Comparison of Voluntary and Electrically-Induced Contractions Voluntary Type I fibers recruited first Asynchronous –Decreases fatigue GTO protect muscles Electrically-induced Type II fibers recruited first Synchronous recruitment –Based on PPS GTOs do not limit contraction

© 2005 – FA Davis Motor-level Stimulation Parameters: Amplitude: Contraction strength increases as amplitude increases Phase duration: 300 to 500 µsec targets motor nerves: –The shorter the phase duration, the more amplitude required –Longer durations will also depolarize pain nerves –Pain often limits quality and quantity of the contraction Pulse frequency: Determines the type of contraction

© 2005 – FA Davis Pulse Frequency Frequency determines the time for mechanical adaptation Lower pps allows more time (longer interpulse interverals) LabelRangeResult Low < 15 pps* Twitch: Individual contractions Medium15-40 pps* Summation: Contractions blend High >40 pps* Tonic: Constant contraction * Approximate values. The actual range varies from person-to- person and between muscle groups

© 2005 – FA Davis Effect of Pulse Frequency on Muscle Contractions 1 pulse per second Twitch Contraction The amount of time between pulses – the interpulse interval – is long enough to allow the muscle fibers to return to their original position 20 pulses per second Summation The amount of time between pulses allows some elongation of the fibers, but not to their starting point. 40 pulses per second Tonic Contraction The current is flowing so rapidly that there is not sufficient time to allow the fibers to elongate

© 2005 – FA Davis Electrical Stimulation Goals Pain Control

© 2005 – FA Davis Pain Control Sensory-levelMotor-LevelNoxious Level Target A-beta fibersMotor nervesA-delta Tissue C fibers Phase < 60 µsec120 to 250 µsec1 msec Duration Pulse60 to 100 pps2 to 4 ppsVariable Frequency80 to 120 pps IntensitySubmotorModerate toTo tolerance Strong contraction

© 2005 – FA Davis Electrical Stimulation Goals Edema Control and Reduction

© 2005 – FA Davis Edema Control Cathode placed over injured tissues High pulse frequency Submotor intensity Thought to decrease capillary permeability Do not use if edema has already formed

© 2005 – FA Davis Edema Reduction Muscle contractions “milk” edema from extremity Electrodes follow the vein’s path Alternating rate targets muscle groups Elevate during treatment

© 2005 – FA Davis Electrical Stimulation Goals Fracture Healing

© 2005 – FA Davis Fracture Healing Electrical current triggers bone growth Piezoelectric effect within the collagen matrix Alternating current –Applied transcutaneously –Similar to diathermy units (no heat production) Direct current –Implanted electrodes

© 2005 – FA Davis Contraindications and Precautions

© 2005 – FA Davis Contraindications and Precautions Areas of sensitivity –Carotid sinus –Esophagus –Larynx –Pharynx –Around the eyes –Temporal region –Upper thorax Severe obesity Epilepsy In the presence of electronic monitoring equipment Cardiac disability Demand-type pacemakers Pregnancy (over lumbar and abdominal area) Menstruation (over lumbar and abdominal area) Cancerous lesions (over area) Sites of infection (over area) Exposed metal implants