Instructor: Prof Enrique Amador
Heat Agents:
Categories:
Superficial: Affects skin and subcutaneous tissues, with limited effect beyond 2 cm (e.g., Hot Packs, Fluidotherapy, Paraffin).
Deep: Affects deeper tissues, goes about 3-5 cm (e.g., Short Wave Diathermy and Ultrasound).
Literature Discrepancy: There are varying numbers regarding the depth of effect.
Historical Background:
Therapeutic ultrasound began in the early 20th century, originally developed from military applications using sonar.
Initial focus was on heating properties, using continuous mode at intensities of 0.5-1.5 watts/cm², primarily studied by scientists rather than clinicians treating patients.
Relevance of Material: Not all chapter content is crucial for practical application in patient care.
Focus: Lecture will emphasize basic physical principles, crucial for understanding clinical applications for thermal and non-thermal effects in both superficial and deep tissues.
Sound Properties:
Sound is a mechanical wave characterized by pressure oscillation in solids, liquids, or gases that can be heard.
Ultrasound operates at frequencies beyond human hearing ranges.
Frequency Range:
Audible Sound: 30-20,000 cycles/second.
Therapeutic Ultrasound: 1-3 million cycles/second (1-3 MHz).
Wave Effects:
When waves travel through media, they cause effects such as vibrations and energy transfer, shifting mechanical energy to thermal energy.
Machine Mechanics:
Ultrasound machines convert electrical currents into mechanical vibrations through crystals in the transducer to produce ultrasound waves.
Key Characteristics:
Frequency, Duty Cycle/Duty Factor, Intensity, Duration.
Impact on Tissue Depth:
Higher frequencies (3 MHz) target superficial tissues, while lower frequencies (1 MHz) penetrate deeper.
Delivery Modes:
Continuous Ultrasound: 100% duty factor, generates thermal effects.
Pulsed Ultrasound: Intermittent intensity (20-50% duty factor), results in non-thermal effects.
Clinical Application: Continuous mode for heating, pulsed mode for inflammation.
Ultrasound Properties: Absorption, Penetration, Reflection, Refraction.
Tissue Absorption: Different tissues absorb ultrasound energy variably: Bone > Muscle > Blood.
Inverse Relation: Higher absorption correlates with lower penetration.
Sound waves may reflect from boundaries, diminishing power as they enter tissues.
Coupling Agent Importance: Essential to mitigate reflection at the transducer-skin interface.
Wave Bending: Occurs at angled boundaries, risking standing waves that may increase energy and cause tissue damage.
Movement Precaution: Keeping the ultrasound head in motion avoids damage.
Definition: Expansion and contraction of gas bubbles in tissues exposed to ultrasound.
Types: Stable cavitation increases cell permeability, while unstable cavitation can harm tissues - mitigate by moving the transducer head.
BNR (Beam Nonuniformity Ratio): Indicates quality; recommended ratios are 5:1 or 6:1.
ERA (Effective Radiating Area): Refers to the size of the effective ultrasound delivery.
Assessment: BNR and ERA determined using hydrophones; periodic safety checks ensure effective delivery and compliance.
Benefits:
Increases nerve conduction velocity, modulation of pain, improved circulation, metabolic rate, reduction of muscle spasms, increases soft tissue extensibility, decreased joint stiffness.
Benefits:
Enhancement of cell membrane permeability, increased intracellular calcium, facilitation of tissue repair, and promotion of normal cell functions.
Determining the required thermal vs. non-thermal effects based on conditions—recognizing variations in treatment for acute versus chronic issues.
Specific Conditions:
Examples include (non-thermal): Acute conditions, calcium deposits, chronic inflammation, etc.
Conditions:
Includes decreased circulation, DVT, active malignancy, and pregnancy. Important for clinicians to remember key contraindications (e.g., pacemaker, pregnancy, cancer).
Transducer Sizes: Commonly from 1-10 cm², with 5 cm² being the most used.
Direct Coupling: Apply a coupling agent before treatment;
Indirect Coupling: Includes using water or gel pads in specific scenarios.
Transducer movement should overlap at a speed of 3-4 cm/s, at 90-degree angles to tissues.
Treatment area should be approximately 2-3 times the ERA, avoiding ultrasound for over 4 times the ERA size.
Determine based on size, depth, and desired effects. Research supports 5 minutes for an area of 2-3 times the ERA, but billing practices necessitate a minimum of 8 minutes.
Non-thermal effects applied early in healing, while thermal effects focus on later recovery stages.
Requires annual inspections, understanding contraindications, ongoing patient assessments, and clear documentation among care personnel.
Definition: Ultrasound used for the transdermal delivery of medications (e.g., anti-inflammatories, analgesics).
Application Modes: Either pulsed or continuous, tailored to minimize tissue heating.