1
Q
What are the key physiological concepts of excitable cell membranes?
A
- resting membrane potential
- semi-permeable membrane
- depolarization
- propagation of action potential
- volume conduction through electrolytes
2
Q
What are the benefits of myelination?
A
- increases speed of conduction
- saves space
- saves energy
3
Q
What are the stimulus amplitude values for nerve and muscle? Pulse duration?
A
nerve: amplitude = -70mV; pulse duration = 1 msec
muscle: amplitude = -90mV; pulse duration = 35 msec
4
Q
Accommodation
A
decreased excitability with slow “rate of rise” (ideal < 60 microseconds); generally want to avoid accommodation with rapid “rate of rise”
5
Q
Law of Dubois Reymond
A
- stimulus amplitude must be sufficiently high to cause depolarization
- the rate of change of voltage must be sufficiently rapid to avoid accommodation
- duration of stimulus must be long enough to overcome latent period and allow action potential and recovery to occur
6
Q
Critical Fusion Frequency (i.e. tetany)
A
Range: 15 to 40 pps
7
Q
High Frequency Fatigue
A
> 50 Hz (occurs rapidly, versus physiological fatigue which occurs slowly, with long recovery period)
Propagation failure - occurs at branch points where motor nerve divides to innervate individual mm fibers
*Review slides from lecture
8
Q
Cation
A
positive ion has lost one or more electrons; cation = cathode (negative pole)
9
Q
Anion
A
negative ion has gained one or more electrons; anion = anode (positive pole)
10
Q
To have current flow, must have:
A
- source of free electrons (+) ions
- material that allows electrons to flow (conductor)
- electromotive force (EMF) that “pushes” electrons
11
Q
What are the three ways to measure amplitude in AC?
A
- peak
- peak-to-peak
- root mean square = .707 x peak value
12
Q
What are the three ways to measure amplitude in AC?
A
- peak
- peak-to-peak
- root mean square = .707 x peak value
13
Q
Impedence
A
resistance - opposes current flow; capacitance - ability of material to store electrical energy by means of electrostatic field; & inductance - ability to store charge by means of electromagnetic field
AC: impedance = res + cap + ind
14
Q
What are the considerations for stimulator output?
A
- wave form
- amplitude
- duration
- duty cycle
- modulation (amplitude, duration, frequency, “rise time”)
15
Q
What are the two types of clinically used electrical stimulation?
A
- Pulsed Current (HVPC and TENS)
- Burst Modulated Alternating Current (Russian and IFC)
16
Q
What are the two types of wave forms?
A
- DC (aka galvanic): continuous and pulsed
- AC (aka faradic)
17
Q
What are the four components of stimulator hardware?
A
- power source (AC or DC)
- oscillator circuit
- output amplifier
- modulating circuit
18
Q
When using a device that uses DC, where should the electrodes be placed?
A
the cathode (-) should be placed directly over the motor point because it allows for a greater concentration of electrons
19
Q
Pfleuger’s Law
A
CCC > ACC > AOC > COC
20
Q
How are patient’s often injured using e-stim?
A
In the electrodes commonly used today, the karaya gum and carbon lattice have a tendency to wear off after a few uses, resulting in more concentration and electrical burns of the patient
21
Q
Electrode Size and Placement
A
both relate to current density; larger electrodes disperse charge, while smaller electrodes concentrate charge
placement goals: parallel to longitudinal direction of mm, over the motor point, and close together (increases stim)
22
Q
How can you decrease impedance?
A
- mild abrasion
- tissue warming
- hydration
- higher frequency signaling
23
Q
Skin impedance depends on the _____ ________, NOT the _____ ________
A
phase duration; pulse frequency
24
Q
Physiologic Effects of Electrical Current
A
- 1 mA = threshold for tingling sensation
- 16 mA = can’t release grip on conductor d/t contraction
- 50 mA = pain and possible fainting
- 100 mA to 3 A = ventricular fibrillation
- 6 A = sustained myocardial contraction, temp resp paralysis, burns
25
Relative Contraindications to NMES
- heart patients
- patients with pacemaker
- carotid sinus/neck stimulation
- use during certain work-related vocations
26
Precautions for NMES
- pregnancy (TENS generally okay; high amplitude, HVPC, IFC, Ionto, NMES: NO!)
- children: ?
- skin lesions: decreased resistance
- electrode, gel, tape: skin reaction
- across the spine/vertebrae: OK
27
Chronaxie Test
- obtain threshold point (ie minimally visible contraction = rheobase)
- set intensity to 2x threshold
- time it takes for the tissue to respond to a stimulus 2x the threshold is the chronaxie
*Hopefully the pt. will move toward the left on the curve*
28
Qualitative test
comparing quality of mm contraction in response to short vs. long duration stimulus
Responses characterized as: twitch vs. tetanic; brisk vs. sluggish; diminished vs. absent
29
Responses to NMES
can be hyper-excitable or hypo-excitable
30
Physiologic effects of NMES
- cellular
- tissue
- segmental
- systemic: decreased pain (release of endogenous opiates with TENS application)
31
Cellular Changes from NMES
- histochemical
- metabolic changes
- membrane changes
- stimulation of fibroblasts/osteoblasts
32
Tissue Changes from NMES
- skeletal muscle contraction
- wound healing
- LIDC: cathode = bactericidal; anode = growth
- HVPC
- tendons/ligaments
33
Segmental Changes from NMES
muscle group contraction, macro-circulation
34
Systemic Changes from NMES
decrease pain (release of endogenous opiates w/ TENS application
35
What are the clinical uses for high amplitude NMES?
- mm weakness
- augment blood flow
- facilitate motor control
36
What are the two types of frequency in high amplitude NMES?
carrier frequency (background) and pulses per second (stop/start per second)
37
NMES - Carrier Frequency
2500 Hz; symmetrical, sinusoidal; "burst modulated"
38
What principles explain the control of force during volitional contraction?
size principle and rate coding
39
Fatigue with high amplitude NMES is due to:
- recruitment order
- high frequency
*Need 40-60 sec of "off time" with every 10 sec "on time" (recovery)*
40
Neural Adaptation
- strength increases precedes increase in mm size
- less contraction intensity needed to produce increase strength
- contralateral limb strength increase
41
What is the rationale for NMES in orthopedic patients?
- muscle weakness
- pain
- edema
- muscle reeducation
42
What is the rationale for NMES in neuro patients?
deficits in transmission, integration of sensorimotor information; NMES stimulates many sensory pathways and integration centers
43
What is the rationale for NMES for stimulating denervated muscle?
- maintenance while awaiting re-innervation (mos to yrs)
| - speed functional recovery after re-innervation
44
Denervation Muscle Loss
1% per day for 60 days; 50% in 1st two weeks
45
What are changes with denervation?
due to neurogenic inflammation; can result in fibrillation, acetylcholine hyper-sensitivity, decreased resting membrane potential, strength duration curve shifts to the right
46
Morphological and Physiological Changes in Denervated Skeletal Muscle
Muscle Atrophy - decreased muscle weight, decrease in muscle contractile protein, decrease in muscle sarcoplasm, decrease in number of muscle fibers
Replacement of muscle by fibrous and adipose tissue
Changes in skeletal muscle excitability - oscillations in resting membrane potential, fibrillation potentials, dispersion of Ach receptors, increase in chronaxie and rheobase, increased size of endplate
47
Goals for patients after denervation
limit edema and stasis, maintain flexibility (PROM), avoid further injury to the muscle or joint splint
48
Pain is a _______ factor
bimodal; it consists of acute pain (mechanical stimuli and heat conveyed by A-delta nerve fibers) and chronic pain (polymodal - mechanical, heat, chemical conveyed on unmyelinated C-fibers)
49
Neurogenic Pain
characterized by burning sensation and results from neuronal damage; autonomic disturbance (RSD/CRPS); CNS - thalamic infarct (stroke)
50
Pattern Theory
no specific nerve endings; pain due to stimulus intensity (frequency), central summation; no "pain stimuli", rather a stimulus which is perceived as painful
Problem: does not take purposefulness of neural complexity seriously
51
Specificity Theory
specific receptors, specific nerve fibers, specific relay sites in spinal cord, specific contacts and association areas in the cortex
Problems: does not explain clinical conditions such as phantom limb, causalgia, pain after dorsal rhizotomy
52
Gate Control Theory
large diameter (A-B) fibers inhibit input from A-delta, C fibers; interneurons of the substantia gelatinosa - rexed lamina I, II, III of spinal cord
53
Opiate Theory
endorphins, enkephalins, morphine; local, central production; spinal cord - enkephalins (1/2 life: minutes) = temporary analgesia
Mid-brain (periaqueductal grey matter): endorphins (1/2 life: hours); sustained analgesia
54
What are the 2nd order neurons present in the substantia gelatinosa?
- wide-dynamic range
- nociceptive specific
- heat-pinch-cold
- spinothalamic tract
55
What two biochemical cascades are important d/t repeated exposure to a pain sensitizer?
- nitric oxide – more substance P and glutamate – increased pain signaling
- protein kinase – more receptor sites on the cell – to allow for binding of pain-causing substances
56
Conventional TENS
- high frequency (100 pps)
- short duration (50-100 µsec)
- low intensity (1-3 times perception)
- effect best explained by the Gate Theory
- more effective with acute pain
57
Acupuncture-like TENS
- low frequency (1-10 pps)
- relatively long duration (100-300 µsec)
- high intensity – maximum tolerance
- effect best explained by the Opiate Theory (local)
- more effective with chronic pain
58
Burst-type TENS
- high frequency
- short duration
- high intensity – trains
- effect best explained by Opiate Theory (central)
- best for deep, throbbing, or chronic pain
59
Contraindications for TENS
- pacemaker
- adverse skin reaction
- pain of unknown origin
- epilepsy
- carotid sinus; SA node
60
TENS electrode placement options
- "bracket" pain
- dermatomal pattern
- trigger points
- "acupuncture" points
61
Factors affecting TENS efficacy
- dosing of TENS (amplitude, repeated use, frequency, long-term use
- interactions with pharmacologic agents (low frequency - less effective; high frequency - more effective)
- patient population
62
HVPC waveform characteristics
- twin-peak monophasic
- short phase duration (5 to 45 µsec)
- very high peak current (2000-2500 mA)
- voltage also very high = "high voltage"
very low total current (1.2-1.5 mA)
63
Benefits of HVPC application
- wound healing
- modulation of pain
- control of tissue edema, joint effusion
64
What are the effective parameters for HVPC to reduce swelling and edema?
- 120 pps
- cathode (-) directly over area of edema
- voltages 10% submotor threshold
- ineffective parameters
65
Interferential Current
- treatment for pain, anecdotal
- slight increase in blood flow and decrease in edema
- no skin less impedance, does not penetrate deeper, not more effective for pain than TENS; less comfortable for some patients
- physiologic effects: negligible
- caution: burns
- conclusion: IFC = large, expensive TENS
66
What is meant by "Current of Injury"
a charge exists between the stratum corneum and the dermis that aids in wound healing
67
ESTR: Negative Pole
bacericidal; constant bombardment of organisms with electrons; depletion of substrates; death of organism
68
ESTR: Positive Pole
tissue growth; galvanotaxic effect; increased # of WBC, increased collagen synthesis, and accelerates wound epithelialization
69
Determinants of number of ions transferred with iontophoresis
- current density at active electrode
- duration of current flow
- concentration of ions in solution
*Does not depend on the size of the electrode or amount of drug placed on electrode
70
Determinants of number of ions transferred with iontophoresis
- current density at active electrode
- duration of current flow
- concentration of ions in solution
*Does not depend on the size of the electrode or amount of drug placed on electrode
71
Anti-Inflammatory Effect of Iontophoresis
- inhibits synthesis of PGE2 and leukotrines
- inhibits migration of scavenger WBCs
- stabilizes lysosomal membrane of inflamed cells
72
Potential Side Effects
- tissue catabolism
- adrenocortical suppression of endogenous hormones
- interaction with insulin dependent diabetics
73
Potential Side Effects
- tissue catabolism
- adrenocortical suppression of endogenous hormones
- interaction with insulin dependent diabetics
74
Contraindications of Iontophoresis
- growth plates in pediatric plates
- pacemakers
- pregnant and nursing women
- patient allergy to drug
- denuded skin and new scar tissue
- diabetic patients
- patient on other medications like blood thinners, ASA, NSAIDs
Electrophysiology
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