E-Stim for pain modulation Flashcards
Levels of physiologic response
- Cellular
- Tissue
- Segmental
- Systemic
Cellular level response
- Excitation of excitable cell membranes
- *Nerve
- *Muscle
- changes in cell membrane permeability
- Protein synthesis
- Stimulation in fibroblast, osteoblast
- Modification of microcirculation
Tissue level response
Requires multiple cellular events
- skeletal muscle contraction
- smooth muscle contraction
- tissue regeneration
Segmental level response
Regional effect of cellular and tissue levels
- modification of joint mobility
- Modification of muscle contractility
- muscle pumping action to change circulation and lymphatic drainage
- an alteration of microvasculature not associated with muscle pumping
- increased movement of charged proteins into lymphatics resulting in fluid moving centrally
Systemic effects
- Analgesic effects as endogenous pain suppressors are released and act at different levels to control pain
- Analgesic effects from the stimulation of certain neurotransmitters to control neural activity in the presence of painful stimuli
Effects of electrical stimulation
- Nerve depolarization
- Muscle depolarization
- ionic effects
Membrane structure
- Phospholipid bilayer
- Receptor proteins: binding site for NTs and neuromodulators
- Channel proteins: form pores through the membrane for ion flow (Na+, K+, Ca+)
- Transport proteins: bind and transport substances through the membrane
Membrane permeability
- Easily permeable to K+
- slightly permeable to Na+
- Impermeable to large, negatively charged proteins and phosphates (anions)
- large number of anions trapped inside the cell
Active transport across membrane
- Na+/K+ pump
- uses ATP for energy
- moves Na+ out and K+ into the cell
- Can move against EFM that tends to oppose their movement
Non-uniform distribution of ions
- Na+ higher in fluid surrounding cell
- K+ and anions higher inside cell
- resultant electrical potential difference
Resting membrane potential
- 90 mV for muscle
- 70 mV for peripheral nerve
- maintained via protein pump
- -3 Na+ out 2 K+ in leads to (-) resting potential
Nerve depolarization: Action potential
- Resting membrane potential
- -70 mV for peripheral nerve
- When stimulus sufficient in amplitude and duration, Na+ channels open rapidly and K+ channels open slowly
- Allows for influx of Na+ rapidly while outflow of K+ is slower
- Net result is change in membrane potential to +30 mV
- when Vm reaches +30-+35 mV, permeability to Na+ decreases and Na+ channels close and K+ channels rapidly open increasing K+ permeability
- K+ ions flow out of cell returning resting potential to -70 mV (repolarization)
Absolute refractory period
time after depolarization when nerve cell cannot be further excited
Speed of conduction
- Depends upon diameter of nerve fiber and myelination of nerve fiber
- large nerve fiber diamter= faster AP travels
- A-Alpha motor nerves- 60-120 m/sec
- A-gamma and A-delta: 12-30 m/sec
- myelinated nerves=faster AP travels
Nodes of Ranvier
gaps in myelin sheath
-AP jumps from node to node in process called saltatory conduction
Peripheral nerve: motor
- cell body: ventral horn or brainstem motor nuclei
- Axon: terminate on muscle ( A-alpha, A-gamma)
Peripheral nerve: sensory
- Cell body: dorsal root ganglia or cranial nerve sensory nuclei
- Axon: 50% end as free nerve endings, 50% as specialized sensory receptors
Peripheral nerve: composition
- Axons of sensory, motor, and autonomic fibers
- Schwann cells
- produce myelin
- insulate fibers from each other
- CT
- epineurium
- perineurium
- ednoneurium
Strength duration curve
graphic representation of minimum combo of current strength (amplitude) and pulse duration (frequency) needed to depolarize that nerve
- lower current amplitudes and shorter pulse durations depolarize sensory nerves (A-beta, A-delta)
- higher current amps and longer pulse durations depolarize motor nerves (A-alpha, A-gamma)
- higher yet current amps and longer pulse durations depolarize pain transmitting C fibers
Strength duration curve: sub threshold
-Amplitude and duration below curve for particular nerve
Strength duration curve: threshold stimulation
amplitude and duration of curve
Strength duration curve: suprathreshold
- amplitude and duration above curve
True or false: peripheral nerve membrane is more excitable than muscle membrane
true
Rheobase
minimum current amplitude with a very long pulse duration required to produce an AP
- current amplitude dependent
Chronaxie
- The minimum duration it takes to stimulate that tissue at twice the rheobase amplitude
- time/duration dependent
Strength duration curve: all or none response
once threshold is achieved, nerve fiber fires
Strength duration curve: accommodation
if stimulus is too slow, nerve can adjust threshold level
Strength duration curve: propagation
- normal physiological stimulation- AP propagated one way only (orthodromic)
- electrical stimulation: AP propagated both ways ( only those transmitted in usual way have effect) (antidromic)
Pain modulation: intensity
intensity controls peripheral nerve axon recruitment
Threshold level stimulation
- a current applied @ an intensity and duration just strong enough to reach threshold will excite only large superficial fibers in mixed nerve
Increased current intensity
- Increased current intensity now excites medium sized superficial fibers and deeper large sized fibers
- further increasing current amp will now excite small, superficial, medium deeper and large deepest fibers
Transcutaneous Electrical Nerve Stimulation: Pain modulation
- Selective stimulation of A-beta fibers can block pain transmission in the spinal cord (gate control theory)
- E-Stim transcutaneously (conventional)
- short pulse duration( 50-80 usec)
- pulse frequencies of 100-150 pps
- Low current amp (tingling)
- will block pain only while stim is on
- may be used 24 hours per day
How do you control for adaptation
- modulate rate
- modulate width
Pain modulation: low rate or acupuncture like TENS
- Frequencies of 2-10 pps
- longer pulse duration (100-200 usec)
- higher current amplitude (visible contraction)
- will control pain for 4-5 hours after a 20-30 min tx
- half life of endogenous opiates is 4.5 hours
- stimulates A-delta nociceptive and A-alpha fibers
Pain modulation: noxious-intensity TENS
- Short duration stim (<1 min)
- can use low frequency (1-5 pps)
- can use high frequency ( 80-110 pps)
- pulse duration: up to 1 sec
- amplitude: 2x motor threshold
- stimulates A-delta and C fiber nociceptors as well as A-alpha and A-beta fibers
- opioid-mediated and nonopioid-mediated analgesia
- serotonin and noradrenaline mediated in cord
- muscarinic mediated supraspinally
Pain modulation: burst mode TENS
- works like low frequency TENS
- stim is delivered in bursts composed of a number of pulses each
- stimulation delivered in bursts or packages of 10 pulses
- pulse duration: 100-300 us
TENS parameters: conventional high rate TENS
- pulse frequency: 100-150 pps
- pulse duration: 50-80 us
- amplitude: to produce tingling
- modulation: if available
- tx time: may be worn 24 hours as needed for pain
- gating at spinal cord
TENS parameters: acupuncture like low rate TENS
- pulse frequency: 2-10 pps
- pulse duration: 100-200 us
- amplitude: to visible contraction
- modulation: NONE
- tx time: 20-30 mins
- Endorphin release
TENS parameters: Burst mode TENS
- pulse frequency: generally preset in unit @ 10 bursts
- pulse duration: generally present and may have max of 100-300 us
- amplitude: to visible contraction
- modulation: not generally possible
- tx time: 20-30 mins
- endorphin release
High frequency TENS studies
- decrease in VAS for pain when compared to SHAM
- higher % improvement vs SHAM at 4 and 8 weeks (greatest at 4 weeks)
Low frequency TENS studies
- LF TENS had better short term response to pain relief vs SHAM
- LF TENS decreased VAS more than SHAM
TENS and chronic pain study
- no difference with LF-TENS vs HF TENS vs SHAM TENS
- likely due to multiple factors affecting chronic state of pain
- led to discussion about reimbursement for TENS for chronic pain
TENS and acute pain study
-HF TENS had decrease usage of meds but no difference in length of stay
Dose response and TENS studies
- greatest relief with frequencies between 20-80 pps with sensory level TENS
- modulated modes of TENS performed better vs constant frequency sensory level TENS
Interferential current: physiological effects
- Depolarize peripheral motor and sensory nerve
Interferential current: therapeutic effects
- Increase pain threshold
- muscle contraction
- muscle pumping
Interferential current: peripheral nerve depolarization leads to..
- sensory fibers gate closing
- *pain management
- evoked tetanic muscle contraction
- pelvic floor contraction which leads to urinary incontinence management
- muscle pumping which leads to blood flow/ edema management
Interferential current: therapeutic purposes
- 50-120 pps > pain management
- stimulating large diameter afferent neurons (ex A-beta fibers)
- 20-50 pps > muscle contraction
- 1 pps > acustim pain relief
Interferential current: indications
- pain of known origin
- possibly for muscle exercise to increase blood flow, muscle relaxation, and edema reduction
High volt pulsed current
- Twin-peaked, monophasic, pulsed current
- driven by characteristically high EMF (current) from 150-500 volts
- 150= high volt stimulator
HVPC: twin peak monophasic pulse
- pair of monophasic spike like waveforms
- almost instantaneous rise followed by exponential decline
- pulse duration- short
- 100-200 usec
HVPC: biophysical characteristics
- HVPC pulses generally fixed by the manufacturer
- some allow for adjustment of interspike interval
- pulse frequency: 1-200 pps (pain of monophasic spike like waveforms)
- versatility
- high volt output an monophasic pulsed waveform allows for; electic neve/muscle stim, and wound healing
HVPC: therapeutic purposes
- 80- 120 pps > sensory TENS pain managment
- stimulating large diameter afferent neurons
- *activates spinal gate (A-beta)
- 30-60 pps > muscle contraction
- 2-4 pps> motor TENS pain relief
- activates endorphin descending loop ( C, a-delta fibers)
