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Lab Details: EMG+

Lab Details: EMG+. Now working with “canned” software Biopac Attach electrodes, reaction switch, headphones, etc. Week 1 Go through tutorial, reaction time Week 2 Measure clench strength (estimated and using data to guide) Lifting 5 lb weights Muscle fatigue Only apply electrodes once!!.

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Lab Details: EMG+

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  1. Lab Details: EMG+ • Now working with “canned” software • Biopac • Attach electrodes, reaction switch, headphones, etc.

  2. Week 1 • Go through tutorial, reaction time • Week 2 • Measure clench strength (estimated and using data to guide) • Lifting 5 lb weights • Muscle fatigue • Only apply electrodes once!!

  3. Week 3-Electrooculogram (EOG) • Track eye movements by measuring muscle performance • Evaluate differences between reading and tracking objects • Can use system to track on a computer screen only using eyes

  4. Week 4-EMG and Goniometer • Goniometer measures angles • Evaluate how well one can hit a target • Does this improve with practice? • How does muscle use change with practice? • Change with weigh/fatigue • Velocity, acceleration, placement

  5. Definition of Electromyography (EMG) • Electromyography (EMG) is the detection and recording of the electrical signal produced by muscle tissue as it contracts.

  6. Definition of Electromyography (EMG) • Electromyography (EMG) includes the • Detection • Amplification • Recording • Analysis • Interpretation of the electrical signal produced by skeletal muscle when it is activated to produce force.

  7. Therefore, the appropriate • Hardware • Software • Anatomical knowledge • are required for interpretation of the EMG data.

  8. At this stage we will consider only surface EMG in which the signal is detected by electrodes placed on the surface of the skin.

  9. Surface EMG • Muscle activation results in electrical activity: • Action potentials on membranes are small currents that can be recorded at the surface of the skin-surface EMG • Is actually a “by-product”-but contains information about level of activity • Measured by EMG electrodes-amplifiers-recorders

  10. Signal is noise-like; temporal and spatial differences between motor units (MUs) • But the stronger the muscle activity, the more action potentials, the stronger the EMG signal • Other factors • Skin impedance (preparation) • Subcutaneous fat • Muscle size • Distance

  11. The detection volume is the volume of muscle tissue contributing to the EMG signal. • The conduction volume is the volume of tissue through which the signal must pass before reaching the electrode. • This includes: • Muscle • Subcutaneous fat • Skin

  12. Determinants of EMG Amplitude • Determinants of the amplitude of the direct EMG signal may be classified broadly as biological or technical. • Biological determinants include • Force of muscular contraction (related to the number of the motor units activated) • Size of muscle • Position of muscle (supervicial vs. deep) • Thickness of subcutaneous fat (an electrical insulator)

  13. Technical determinants include • Skin preparation (determines skin impedance) • Distance between electrodes • Position of electrode relative to muscle (proximal vs. distal) • Orientation of electrodes (with respect to muscle fiber direction)

  14. Each muscle cell is packed with protein fibers called myofibrils and is a collection of sarcomeres separated by Z-discs. Sarcomeres are the smallest contractile unit in a muscle fiber. Sarcomeres contains two main types of protein fibers: Myosin- the thicker filament and Actin – the thinner filament. When activated, the contraction is produced by sliding of the myosin fibers over the actin fibers in each sarcomere, which in turn produces a contraction of the muscle cell. The striation seen in the skeletal muscle tissue under the microscope is due to the orderly arrangement of thick and thin filaments.

  15. Muscle Contraction • The action potential changes the permeability of sarcoplasmic reticulum which releases Ca++ ions. • Ca ions bind with a protein molecule which opens the binding site and actin and myosin bind together. • Myosin molecule binds with energy molecule and changes shape and thus produces a sliding motion over the actin filament, which contracts the muscle.

  16. Muscle Contraction • At the end of a contraction, Ca ions are transported back. Actin – myosin filaments detach from each other and muscle relaxes by the passive tension of the connective tissues.

  17. The Motor Unit • The motor unit (MU) consists of a single nerve fiber (neuron) and all of the muscle fibers it innervates. Extraocular muscles have about 5-6 muscle fibers per motor unit for fine control, while large muscles of the lower limb such as gluteus maximus and gastrocnemius (calf) have about 2000 muscle fibres per motor unit, allowing only relatively coarse control. • During neural activation of muscles each complete motor unit is either on or off. Each muscle consists of multiple MUs, from just a few to many thousands.

  18. Electrical Response to Neural Activation • Muscle activation results in electrical activity: • To produce a smooth contraction there is overlapping of motor unit firing (5-100 pulses/s but commonly 10-30 pulses/s). A fundamental principle governing muscle contraction is that there are asynchronous volleys of impulses traveling down the many axons innervating a single muscle.

  19. Only muscle tissue contributes to the EMG signal. Therefore, connective tissue can produce passive force but does not produce an electrical response.

  20. Quantification of EMG • Methods of quantification and interpretation of EMG are still being developed. In some studies the basic information required is related to temporal factors. When does the muscle become active? When does it become inactive? For this type of study, "ON" and "OFF" times need to be determined.

  21. As a representation of the energy in the complex polyphasic AC EMG signal, it can be modified and simplified in a variety of ways. • One method of quantification is to • Full-wave rectify the signal (all negative voltages are converted to positive) • Integrate the signal by calculating the area under the curve during a certain period • Calculate the mean amplitude during each period

  22. EMG is not absolute; it is a relative measure only. • Based on EMG, we cannot compare directly between muscles or between people. • We can use EMG values to compare between different conditions for same muscle. • Knowledge of anatomy and physiology essential for correct interpretation.

  23. Transdermal Drug Delivery (TDD) • Diffusion of the medication (drug) through skin into the systemic circulation for distribution and therapeutic effect • Most TDD systems use passive delivery

  24. Advantages of TDD Systems • Reduces first-pass effect and GI incompatibility • Sustains therapeutic drug levels • Permits self-administration • Non-invasive (no needles or injections) • Improves patient compliance • Reduces side effects • Allows removal of drug source

  25. Limitations of TDD Systems • Poor diffusion of large molecules • Skin irritation

  26. Matrix Reservoir Drug-in-Adhesive Multi-Layer Drug-in-Adhesive Single-Layer Backing Drug Membrane Adhesive Liner/Skin TDD Patch Construction Introduction to Transdermal Drug Delivery

  27. Biosensors, e.g. Glucowatch • Biographer: non-invasive, watch-like device that measures glucose • AutoSensor: a plastic part that snaps into the Biographer and sticks to the skin. • Noninvasive & automatic reading every 10 mins up to 13h

  28. Based on reverse iontophoresis: • Glucose pulled through the skin by charged molecules • The ions migrate to the anode (+) and cathode (-) • Glucose reacts with glucose oxidase to form hydrogen peroxide • The reaction produces an electrochemical measured by the AutoSensor • Reverse iontophoresis: future insulin delivery method in response to glucose?

  29. Comparison of Glucose Readings

  30. How does Glucowatch work? • Based on reverse iontophoresis • A low electric current pulls glucose through the skin. Glucose is accumulated in two gel collection discs in the AutoSensor. • Another electrode in the AutoSensor measures the glucose.

  31. How does Reverse Iontophoresis work? • Application of low level direct current will • Attract anionic compounds to the anode • Attract cationic and neutral substances to the cathode • Carry along other compounds by electroosmosis • like glucose

  32. Glucose and Glucowatch • Applies 0.3 mA/cm2 • First model ran for 20 minutes, now < 10 • Works with very sensitive platinum-based amperometric biosensor in watch

  33. Enzymatic pathway • Glucose oxidase catalyze oxidization of glucose in hydrogel • Hydrogen peroxide reacts on the platinum electrode, providing electrons • Current is proportional to glucose

  34. Glucowatch Data

  35. Glucowatch Data

  36. In vitro model-Connolly • Solution of glucose • Cellulose ester membrane (skin) • Applied 70 µA for 15-90 minutes • Cathode and anode solution 300 µl

  37. Insulin Pump Therapy • Example: MiniMed Pump • 1.9 x 3.4 x 0.8 inches, less than 100 grams, about the size of a beeper • Deliver short acting insulin • Basal and bolus dose with remote control • Pump gives better control than injections • Safety Concerns Unique to pump Use: no emergency supply of insulin and skin infections From: http://www.minimed.com/index1.html

  38. What good is this? • Using the Glucowatch Biographer for life can… • Delay the development of the first serious diabetes complication by 4.1 yr. • Treating 18 subjects would prevent one case of blindness and 1.4 cases of renal failure.

  39. Iontophoresis • Iontophoresis • Move drugs into blood stream using electricity • Reverse Iontophoresis • Move something out of blood stream using electricity

  40. Reverse Iontophoresis Lab • Prepare gelatin films containing glucose • Beta glucose only • Attach cylindrical “pucks” with electrodes on top of gelatin at a known distance, power, time, solvent and apply current to pull glucose out of film into solution in center of puck

  41. Reverse Iontophoresis Lab • Evaluate variables to determine effect on movement of glucose • New/old spot usage • Glucose concentration • Power applied • Water vs. buffer • Distance between electrodes • Time

  42. Variables

  43. Specifically…

  44. Week 1 • Prepare gelatin films for new/old spot placement analysis • Make 4 solutions, pour each beaker into 3 dishes for a total of 12 dishes of gelatin, 6 at each concentration • Make sure understand how iontophoresis system works

  45. Week 2 • Use 12 dishes from last week to evaluate new/old spot placement • Use saline, 1 minute power, low power, high distance and both concentrations • Make 3 beakers each worth of gelatin at low and high and 1 at zero glucose concentrations, pour beakers into 3 dishes each or a total of 21 dishes

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