Russian Currents - Electrotherapy (2nd Year BPTH)

Q1. Explain Russian Currents and its Pulse Duration, Frequencies

Definition

Waveform

• Type: Sinusoidal (AC) waveform
• Nature: Burst-modulated (the carrier frequency is delivered in on-off bursts/packets)
• The current is symmetrical and biphasic, so there is no net DC component - making it safe with minimal skin irritation.

Technical Parameters / Characteristics

Why 2500 Hz?

On : Off Time (Treatment Protocol - 10/50/10 Rule)

• 10 seconds = muscle contraction time (on time)
• 50 seconds = rest/relaxation time (off time)
• 10 repetitions per session

Frequencies - Detailed Breakdown

• At 50-70 Hz burst frequency: produces tetanic (sustained) muscle contraction - used for strengthening
• At 35-50 Hz burst frequency: produces rhythmic pumping - used for oedema reduction

Q2. Brief Introduction of Effects and Uses of Russian Currents

Physiological Effects

1. Neuromuscular excitation - The 2500 Hz carrier activates motor nerves efficiently with reduced discomfort due to lower skin impedance at medium frequency.
2. Tetanic muscle contraction - Burst frequency of 50-70 Hz causes sustained (tetanic) contraction similar to a voluntary maximal effort, stimulating fast-twitch (Type II) muscle fibers preferentially.
3. Muscle strengthening - Repeated tetanic contractions cause muscle hypertrophy and increased strength comparable to voluntary exercise (Kots claimed up to 30-40% strength gains).
4. Improved blood circulation - Rhythmic muscle contraction increases local blood flow and venous/lymphatic return.
5. Oedema reduction - Muscle pumping action at lower burst frequencies reduces peripheral oedema by enhancing lymphatic drainage.
6. Re-education of muscle - Helps re-establish neuromuscular pathways in post-surgical or post-injury patients.
7. Reduced muscle fatigue (compared to low-frequency NMES) - Medium frequency causes less electrochemical changes under electrodes, so patients tolerate higher intensities for longer.

Clinical Uses / Indications

1. Muscle strengthening - Primary use; especially in healthy athletes and post-operative patients.
2. Post-knee surgery rehabilitation:
   • Post-ACL reconstruction
   • Post-knee ligament surgery
   • Post-arthroscopic knee surgery
3. Quadriceps strengthening (most common clinical application)
4. Prevention of disuse atrophy - Post-immobilisation, post-fracture
5. Following ligament sprains - Regaining muscle bulk
6. Oedema reduction - Using lower burst frequency (35-50 Hz) for muscle pumping
7. Athletic performance enhancement - Sport-specific conditioning

Contraindications

• Anterior cervical region (risk of laryngospasm/cardiac arrhythmia)
• Transthoracic application (cardiac risk)
• Lumbar/abdominal area in pregnancy
• Over hemorrhagic areas
• Over neoplastic (cancerous) areas
• Over metallic or electronic implants (pacemakers)
• Over areas of impaired skin sensation
• Thrombosis / thrombophlebitis

Treatment Parameters Summary (Exam Table)

Comparison: Russian vs. Standard NMES

Key Points to Remember for Exam

• Russian current = medium-frequency AC, carrier 2500 Hz, burst 50 Hz
• Pulse duration: 200-400 µs
• Duty cycle: 50% (10 ms on : 10 ms off)
• Protocol: 10/50/10 (10 sec on, 50 sec off, 10 reps)
• Primary indication: muscle strengthening, especially quadriceps post-knee surgery
• Invented by: Dr. Yakov Kots, USSR (1970s)
• Advantage over conventional NMES: greater comfort + deeper penetration due to medium frequency

Strength-Duration Curve (SDC) - Complete Exam Answers

Q1. Explain Principles of S-D Curve

Definition

• Y-axis (vertical): Stimulus intensity (in milliamperes - mA or volts - V)
• X-axis (horizontal): Pulse duration (in milliseconds - ms), ranging from 0.01 ms to 300 ms
• The current used is rectangular (square wave) galvanic/direct current

Basic Principle

"As the pulse duration increases, less intensity (current) is needed to produce a contraction. Conversely, as pulse duration decreases, more intensity is required."

Underlying Physiological Principles

1. All-or-None Law: A single muscle fiber either contracts completely or not at all. The SDC plots the minimum threshold to achieve this.
2. Accommodation: Nerve fibers can adapt (accommodate) to slowly rising currents and may not fire. Denervated muscle lacks this property - this difference is the basis of SDC interpretation.
3. Excitability: The SDC reflects the excitability of nerve and muscle tissue. A normal nerve-supplied muscle responds at short pulse durations (high excitability). A denervated muscle requires longer durations.
4. Wallerian Degeneration: After nerve injury, distal axons degenerate (Wallerian degeneration) over 7-21 days. SDC testing is done 10-14 days after injury to allow full degeneration to be reflected in the curve.

Clinical Significance / Purpose of SDC

• Assess nerve integrity following peripheral nerve injury
• Detect denervation of muscles
• Monitor progress of nerve regeneration
• Plan electrotherapy treatment (appropriate pulse duration selection)
• Can be performed as early as 10-14 days after nerve lesion
• Nerve regeneration typically begins after 21-22 days and may take up to 270 days

Q2. Define Chronaxie and Rheobase

Rheobase

Rheobase is defined as the minimum intensity of current (using infinite/long pulse duration) required to produce a just-visible muscle contraction.

• It is measured at the longest pulse durations (100-300 ms) where current requirement plateaus
• The pulse used is always rectangular
• Measured in milliamperes (mA) or volts (V)

• Rheobase is greater (higher) in denervated muscles
• Partial denervation generally causes no change in rheobase
• Factors affecting rheobase: skin resistance, oedema, ischaemia, electrode position, temperature, subcutaneous tissue thickness

Chronaxie

Chronaxie is defined as the minimum time (pulse duration) for which a current of TWICE the rheobase intensity must flow to produce a just-visible muscle contraction.

• It is read off the SD curve by: first finding rheobase → doubling that value on the Y-axis → drawing a horizontal line across to the curve → dropping a vertical line to the X-axis
• Measured in milliseconds (ms)

• Chronaxie is inversely proportional to excitability (higher chronaxie = less excitable = more denervated)
• Chronaxie is the most useful single value from the SD curve
• Factors affecting chronaxie: denervation, re-innervation, nerve root lesion, peripheral neuropathy, ischaemia, oedema, fatigue, myopathy (no significant change in myopathy)

Utilization Time

• The time at rheobase intensity = Utilization Time (also called "rheobasis time")
• Normal utilization time for motor nerves: ~3 ms

Q3. Describe Techniques of Plotting the S-D Curve

Equipment Required

• Constant current electrical stimulator (galvanic/DC)
• Supplies rectangular impulses of variable duration: 0.01, 0.03, 0.1, 0.3, 1, 3, 10, 30, 100, 300 ms
• Active (motor point) electrode - small pencil/point electrode
• Dispersive (indifferent) electrode - larger pad electrode
• Graph paper / SD curve chart
• Electrode jelly / wet cotton

Patient Preparation

1. Explain procedure to patient; patient should be relaxed
2. Position patient comfortably with the muscle to be tested exposed
3. Clean skin over the motor point area
4. Locate the motor point of the muscle to be tested (point on the muscle belly where minimum current produces maximum contraction)

Electrode Placement

• Active electrode (cathode/negative): Small pencil-type electrode placed over the motor point of the muscle
• Dispersive electrode (anode/positive): Large pad electrode placed over a nearby inactive area (proximal to the motor point)
• The active electrode must remain at the same motor point throughout the entire test

Step-by-Step Procedure

1. Start with the longest pulse duration (300 ms or 100 ms)
2. Gradually increase the intensity (current/voltage) until a just-visible (minimal) contraction is produced
3. Record the intensity at this threshold
4. Shorten the pulse duration to the next value (e.g., 100 → 30 → 10 → 3 → 1 → 0.3 → 0.1 → 0.03 → 0.01 ms)
5. At each shorter pulse duration, increase intensity as needed to again produce a minimal contraction
6. Record all intensity values at each pulse duration
7. Plot the values on graph paper: X-axis = pulse duration (ms, log scale), Y-axis = intensity (mA or V)
8. Connect the points to draw the curve

Note: A minimal/threshold contraction is used (not maximal) to make it easy to detect any change in strength required, and to improve sensitivity.

Important Notes During Plotting

• Use constant current stimulator (preferred over constant voltage)
• Keep the active electrode at exactly the same motor point throughout
• Test the normal (unaffected) side first for comparison
• Observe the quality of contraction (brisk vs. sluggish) in addition to intensity values
• Sluggish, worm-like contraction at long durations = sign of denervation

Q4. Explain & Differentiate Characteristics of SDC for Innervated and Denervated Muscles; Identify Abnormal Curves

A. INNERVATED MUSCLE (Normal / "Nerve Curve")

• Shape: Rectangular hyperbola - smooth, continuous curve
• The curve rises steeply to the left (at short durations below 1 ms)
• At longer durations (>10 ms), the curve is relatively flat (plateau/rheobase level)
• Kink: Absent
• Chronaxie: < 1 ms (short)
• Rheobase: 2-18 mA (normal)
• Contraction quality: Brisk, sharp, quick twitch
• The curve is positioned to the left of the graph
• Responds to short pulse durations because nerve fibers have high excitability

B. COMPLETELY DENERVATED MUSCLE ("Muscle Curve")

• Shape: Steep curve, shifted markedly to the RIGHT
• The curve continues to rise even at long pulse durations (does not plateau as early)
• Does not respond at very short durations (< 1 ms)
• Kink: Absent (smooth but displaced right)
• Chronaxie: > 1 ms (greatly prolonged - can be 10-100 ms)
• Rheobase: Higher than normal
• Contraction quality: Sluggish, worm-like, slow contraction (characteristic of denervation)
• Represents stimulation of muscle fibers directly (no nerve)
• The shift right occurs because denervated muscle fibers have very low excitability

C. PARTIALLY DENERVATED MUSCLE

• Both innervated and denervated fibers are present
• Shape: Curve shows a characteristic KINK (discontinuity/step)
• The right side of the kink represents the denervated fibers
• The left side of the kink represents the surviving innervated fibers
• Two portions of the curve are visible (nerve curve component + muscle curve component)
• The degree of the kink reflects the extent of denervation

Comparison Table (Most Important for Exam)

Abnormal Curves - Identification

Key clinical note: As re-innervation occurs, the curve progressively shifts back toward the left (toward normal). This is used to monitor recovery.

Q5. Demonstrate and Plot SDC on Models

1. Position the model comfortably (e.g., supine for testing tibialis anterior)
2. Locate the motor point using a motor point chart and a scanning electrode with low-level current - find the point giving maximum contraction with minimum current
3. Place electrodes: Small active electrode on motor point; large dispersive electrode proximally
4. Set stimulator to rectangular pulse, constant current
5. Begin at 300 ms duration, gradually increase intensity until minimal twitch seen - record mA
6. Reduce to 100 ms, repeat - record mA
7. Continue: 30 ms → 10 ms → 3 ms → 1 ms → 0.3 ms → 0.1 ms → recording at each
8. Plot values on graph: Y-axis = mA, X-axis = ms (log scale)
9. Draw and label: Rheobase (horizontal line at plateau), Chronaxie (mark at 2 x rheobase on Y, drop to X-axis)
10. Compare with normal side or reference values
11. Interpret the curve shape (normal / partial / complete denervation)

Q6. Observe SDC in Patients in Clinical Area

1. Indication for the test - Why is SDC being performed? (e.g., facial palsy, foot drop, wrist drop, brachial plexus injury, radiculopathy)
2. Patient positioning and preparation
3. Motor point location technique used by the therapist
4. Type of equipment used (constant current stimulator, impulse durations available)
5. Procedure followed - starting duration, how intensity is adjusted, how minimal contraction is defined
6. Quality of contraction - Is it brisk (innervated) or sluggish/worm-like (denervated)?
7. Plotting of the curve - Values recorded, graph plotted
8. Interpretation by the supervising therapist:
   • Is there a kink? (partial denervation)
   • Is the curve shifted right? (complete denervation)
   • Is chronaxie prolonged?
9. Comparison with previous SDC to assess progress of nerve regeneration
10. How findings guide treatment (e.g., selection of pulse duration for electrical stimulation)

Summary Memory Chart (Exam Quick Revision)