Medical Instrumentation Systems Overview
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Questions and Answers

What occurs at the electrode-electrolyte interface when there is a concentration mismatch?

A change in the distribution of ions occurs due to a difference in the concentration of ions.

What is the behavior of perfectly polarizable electrodes?

No charge crosses the electrode-electrolyte interface, and they behave like capacitors.

How do perfectly non-polarizable electrodes differ from polarizable ones?

Current passes freely across non-polarizable electrodes, and there is no overpotential.

What is represented by Ehc in the circuit model of electrode behavior?

<p>Ehc represents the half-cell voltage, similar to a battery in the circuit model.</p> Signup and view all the answers

What is the typical amplitude range of EEG signals?

<p>EEG signals typically have an amplitude range of 1-10 µV.</p> Signup and view all the answers

What is the bandwidth range for EEG signals?

<p>The bandwidth for EEG signals is 0.5-40 Hz.</p> Signup and view all the answers

What is a key application of EEG monitoring?

<p>EEG is used for sleep studies and seizure detection.</p> Signup and view all the answers

What type of noise is a common source of error in EEG recordings?

<p>Thermal noise and 50Hz power line interference are common sources of error.</p> Signup and view all the answers

What is the primary role of a transducer in medical instrumentation?

<p>A transducer converts one type of energy into another, typically turning physical parameters into electrical signals.</p> Signup and view all the answers

What does EOG stand for and what does it measure?

<p>EOG stands for Electrooculography, which measures the electrical potential and motion of the eyes.</p> Signup and view all the answers

Distinguish between direct and indirect measurement in sensing.

<p>Direct measurement occurs when a sensor measures the parameter of interest directly, while indirect measurement involves measuring another parameter that can be converted to the desired measurement.</p> Signup and view all the answers

Describe the primary purpose of EMG.

<p>EMG, or Electromyography, measures the electrical activity of muscle fibers to evaluate muscle function.</p> Signup and view all the answers

List the primary energy forms that a transducer can convert.

<p>Mechanical, thermal, electromagnetic, optical, and chemical energy forms.</p> Signup and view all the answers

What is the gait cycle and how is it divided?

<p>The gait cycle is the complete sequence of movement from one heel contact to the next by the same foot, divided into stance and swing phases.</p> Signup and view all the answers

What are the conditions necessary for electrocution to occur?

<p>A path for current flow must exist, with two points of contact on the body, and the current must pass near the heart.</p> Signup and view all the answers

What percentage of the gait cycle time does the stance phase occupy?

<p>The stance phase occupies 60% of the gait cycle time.</p> Signup and view all the answers

Identify one type of temperature sensor and describe its function.

<p>Resistance Temperature Devices (RTDs) function by changing resistance with temperature, providing temperature measurement.</p> Signup and view all the answers

List two applications of gait analysis.

<p>Gait analysis is used to diagnose and treat conditions, and to track treatment impact after surgery.</p> Signup and view all the answers

Explain the significance of calibration in medical instrumentation.

<p>Calibration ensures that instruments provide accurate and reliable measurements by aligning them to known standards.</p> Signup and view all the answers

How does the EOG relate to sleep states?

<p>EOG measures eye movement, which is relevant for analyzing different sleep states.</p> Signup and view all the answers

What is the threshold of death in terms of current level?

<p>The threshold of death occurs when the current reaches between 50-500mA, which can cause ventricular fibrillation.</p> Signup and view all the answers

What is the role of the vestibulo-ocular reflex as related to EOG?

<p>The vestibulo-ocular reflex helps stabilize vision by coordinating eye movement with head movement.</p> Signup and view all the answers

Describe the purpose of signal conditioning in a medical instrumentation system.

<p>Signal conditioning involves amplifying and filtering the sensor's output to prepare it for further processing or display.</p> Signup and view all the answers

Explain how EMG can be used in sports medicine.

<p>EMG is used in sports medicine to enhance athletic performance by analyzing muscle activation patterns.</p> Signup and view all the answers

What are the three phases of the swing phase in gait analysis?

<p>Initial swing (acceleration), mid swing, and terminal swing (deceleration).</p> Signup and view all the answers

Name two wearable systems for gait analysis.

<p>IMU (Inertial Measurement Unit) and accelerometers.</p> Signup and view all the answers

What is the function of an extracellular recording electrode?

<p>It measures the electrical activity of neurons from outside the cell membrane.</p> Signup and view all the answers

List the signal acquisition techniques in order of spatial resolution, starting from the highest.

<p>SUA, MUA, LFP, ECoG, MEG and EEG.</p> Signup and view all the answers

What is the role of a pacemaker in cardiac function?

<p>A pacemaker regulates the heart's beating using electrical impulses when the heart does not stimulate properly on its own.</p> Signup and view all the answers

Describe the first degree SA block arrhythmia.

<p>There is a delay between sinus node activation and atrial activation.</p> Signup and view all the answers

What is one disadvantage of using flexible surface electrode arrays?

<p>It is difficult to manage a large number of wires out of the brain.</p> Signup and view all the answers

Identify one medical use of accelerometry.

<p>Gait and balance measurement.</p> Signup and view all the answers

What factors influence the quality of a PPG signal?

<p>Location, blood oxygen saturation, blood flow rate, skin temperature, and the measuring environment influence PPG signal quality.</p> Signup and view all the answers

What are the main design factors that affect the choice and design of PPG instruments?

<p>Design factors include signal factors like sensitivity and reliability, environmental factors such as stability and humidity, medical factors like invasiveness and electric safety, and economic factors such as cost and warranty.</p> Signup and view all the answers

Describe the steps involved in the design process of a medical device.

<p>The design process involves initial design, prototype testing, final design, TGA approval, and production.</p> Signup and view all the answers

What is the role of the Therapeutic Goods Administration in Australia regarding medical devices?

<p>The Therapeutic Goods Administration regulates medical devices to ensure their safety, effectiveness, and quality for public health.</p> Signup and view all the answers

What is a major cause of sudden amplitude changes in PPG waveforms?

<p>Sudden amplitude changes in PPG waveforms are mainly caused by the automatic gain controller.</p> Signup and view all the answers

What are the two main components of a pacemaker?

<p>The two main components of a pacemaker are the pulse generator (battery) and leads or wires.</p> Signup and view all the answers

Distinguish between asynchronous and synchronous pacemakers.

<p>Asynchronous pacemakers operate at a fixed rate without coordinating with the heart's activity, while synchronous pacemakers coordinate with the heart's natural pacemaker activity.</p> Signup and view all the answers

What type of arrhythmia is characterized by uncoordinated heart cell beating?

<p>Ventricular fibrillation is characterized by uncoordinated beating of heart cells.</p> Signup and view all the answers

What is the primary function of an automated external defibrillator?

<p>The primary function of an automated external defibrillator is to automate the diagnosis and treatment of treatable cardiac rhythms.</p> Signup and view all the answers

List two types of defibrillators based on electrode placement.

<p>The two types of defibrillators based on electrode placement are internal and external defibrillators.</p> Signup and view all the answers

What type of signal processing is used in implantable automatic defibrillator systems?

<p>Signal processing in implantable automatic defibrillators uses electrical and mechanical signals to control stimulation.</p> Signup and view all the answers

How does photoplethysmography (PPG) differ from impedance-based plethysmography?

<p>Photoplethysmography measures light absorption variations due to blood volume changes, while impedance-based plethysmography measures changes in impedance related to blood volume variations.</p> Signup and view all the answers

What is the purpose of analyzing the first and second derivatives of the PPG wave?

<p>Analyzing the first and second derivatives of the PPG wave facilitates interpretation and helps in recognizing inflection points.</p> Signup and view all the answers

Flashcards

Measurand

The physical quantity or parameter being measured, either internal or external.

Sensor

A transducer that converts physical energy into an electrical output signal.

Direct measurement

A sensor directly measures the desired parameter.

Indirect measurement

A sensor measures a related parameter that represents the parameter of interest.

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Electrocution condition

Current flowpath must go through or near the heart, with two body contact points.

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Transducer

Converts one form of energy to another.

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Electrical Safety Condition

A path for current, two points of contact on the body (current entry & exit),current must nearby or through the heart.

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Temperature Sensors

Measure temperature using resistance, thermoelectric, radiation, or fiber optics.

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EOG

Electrooculography measures eye movement potential

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EMG

Electromyography measures muscle electrical activity

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Gait Analysis

Systematic study of walking to diagnose, treat, and assess performance

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Gait Cycle

Full cycle of a limb from heel contact to next heel contact

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Stance Phase

Part of gait cycle where limb is on ground, maintaining balance

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Swing Phase

Part of gait cycle where limb moves forward

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Electrooculography (EOG) Amplitude

Eye movement potential measured in microvolts (µV), typically ranging from 10 to 100 µV

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Electromyography (EMG) Amplitude

Muscle electrical activity measured in millivolts (mV), typically ranging from 1 to 10mV

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Ohmic Resistance

Voltage drop due to current encountering resistance.

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Concentration Polarization

Difference in ion concentration at the electrode-electrolyte interface, affecting current flow.

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Activation Polarization

Electrochemical reaction kinetics determine the rate of current flow.

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Perfectly Polarizable Electrode

No charge transfer across the electrode-electrolyte interface; behaves like a capacitor.

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Perfectly Non-Polarizable Electrode

Free charge transfer across the electrode-electrolyte interface with minimal energy.

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Overpotential

Extra voltage needed to drive a reaction at a given rate beyond the theoretical value.

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EEG Signal

Measures the electrical activity of the brain from the scalp.

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Biomedical Signal Characteristics

Amplitude, bandwidth, sources of error, and applications of different signals.

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PPG Signal Quality Factors

PPG signal quality depends on location, blood oxygen saturation, blood flow rate, skin temperature, and the measuring environment.

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PPG Waveform Distortions

PPG waveforms can show distortions caused by heart rate, blood flow, or arteriole changes.

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PPG Noise Interference

Powerline interference is a common form of noise affecting PPG signals.

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Medical Device Design Factors

Instrument design considers signal factors (sensitivity, range, linearity, reliability), environmental factors, medical factors, and economic factors.

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Therapeutic Goods Administration (TGA)

TGA is the Australian regulatory agency for medical devices.

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Swing Phase of Gait

The portion of the gait cycle where the limb moves forward, divided into initial swing (acceleration), mid-swing, and terminal swing (deceleration).

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Wearable Gait Analysis

Gait analysis using devices like IMUs, EMGs, gyroscopes, etc., worn directly on the body.

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Intracellular Recording

Measuring neuron action potentials by inserting a micropipette into the neuron.

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Extracellular Recording

Measuring neuron electrical activity from outside the cell membrane.

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Pacemaker Function

Regulating heartbeats using electrical impulses, stimulating the heart to beat properly.

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3rd Degree AV Block

Heartbeat condition where no impulses from the sinus node reach the atria, leaving only ventricular escape.

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1st Degree AV Block

Delayed signal between the sinus node and atrial activation.

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Electrode Array Types

Various arrangements for recording neural signals, including one-dimensional (e.g., Neuropixels), two-dimensional, and three-dimensional (e.g., Blackrock/Utah array).

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Pacemaker Types

Pacemakers are categorized by how they synchronize with the heart's natural rhythm: sequential (single or dual chamber), asynchronous (fixed rate), and synchronous (demand).

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Ventricular Fibrillation

An irregular heartbeat where the heart's cells beat randomly; causing loss of blood pressure and an erratic ECG.

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Defibrillation

Using electrical energy to restore a normal heart rhythm.

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Automated External Defibrillator (AED)

A device that automatically diagnoses and treats potentially fatal heart rhythms.

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Plethysmograph

An instrument that measures changes in blood or air volume, primarily in limbs or lungs.

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Photoplethysmography (PPG)

A method of measuring blood volume changes using light absorption.

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Implantable Defibrillator Parts

Implantable devices monitor heart rhythm, provide power, and use electrodes to deliver stimuli if needed.

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Plethysmograph Types

Plethysmographs include optical sensor (photoplethysmography), impedance-based, and water displacement methods.

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Study Notes

Medical Instrumentation System

  • A generalized system includes input (measurand), a sensor, signal conditioning, signal processing, feedback & control, data displays, storage, and transmission.
  • Measurand: The physical quantity or parameter being measured. (Internal or external)
  • Sensor: A transducer that converts physical energy to an electrical signal.
  • Signal Conditioning/Processing: Amplifies or filters signals for improved readability.
  • Output: Displayed in a readable format.
  • Feedback/Control: Used to correct measured parameter or change behavior by or without clinician intervention.

Sensors and Transducers

  • Transducer: Converts one type of energy to another, e.g., physical to electrical.
  • Sensor: Converts physical parameters into electrical outputs.
  • Actuator: Converts electrical input into a physical output.
  • Primary Energy Forms: Mechanical, thermal, electromagnetic, optical, and chemical energy.
  • Direct Measurement: Sensor measures the parameter of interest.
  • Indirect Measurement: Sensor measures a related parameter that can be translated to the parameter of interest

Types of Temperature Sensors

  • Resistance Temperature Devices (RTDs)
    • Resistance changes in response to temperature.
  • Thermistors: Another type of temperature sensor.
  • Thermoelectric Couplers: Generate a voltage in response to temperature differences.

Electrical Safety

  • Electrocution conditions require a current path, contact points on the body, and a path near the heart.
  • Threshold of perception (0.5-2mA): The initial feeling of stimulation.
  • Let-go current: The amount of current causing pain.
  • Maximum Let-go current: Highest pain tolerance level with muscle control.
  • Threshold of death: Current causing ventricular fibrillation (50-500mA).

Static Characteristics of Medical Instruments

  • Describes instrument performance for DC and very low frequency inputs. Key factors include:
    • Accuracy
    • Precision
    • Resolution
    • Tolerance
    • Sensitivity
    • Calibration
    • Drift
    • Input Range
    • Input Impedance

Dynamic Characteristics of Medical Instruments

  • Uses differential equations, describing instrument quality,
    • Complete characteristics = Static + Dynamic characteristics

Biopotentials

  • Biopotentials are voltage differences between internal and external medium due to electrochemical activity of excitable cells.
  • Key ions include Sodium (Na), Potassium (K), and Chlorine (Cl).
  • These potentials transfer information between and within cells.

Nernst Equation

  • Determines the equilibrium potential across a membrane for a specific ion.

Goldman-Hodgkin-Katz Equation

  • Determines the overall membrane potential.

Neurons

  • Axons: Carry messages between somas throughout the body.
  • Nodes of Ranvier: "Signal regenerators" along axons.

Action Potentials

  • Describes the changes in membrane potential over time.

Electrodes

  • The interface between metal and electrolyte that forms a half-battery.
  • Anode: Metal oxidizes, releasing cations into electrolyte; electrons flow toward cathode.
  • Cathode: Metal reduces, gaining electrons from anode, attracting anions from electrolyte.
  • Polarization: Current between electrode and electrolyte alters half-cell potential.
  • Overpotential: Difference between observed and theoretical potential.
  • Types of Electrode Issues:
    • Ohmic/Resistance: Resistance slows current flow.
    • Concentration: Mismatch in ion concentration rates across the interface.
    • Activation: Kinetics of electrochemical reaction influence.

Perfectly Polarizable and Nonpolarizable Electrodes

  • Perfectly polarizable: No charge transfer, acts like a capacitor (e.g., stimulation).
  • Perfectly nonpolarizable: Free charge transfer (e.g., recording)

Electrode Arrays

  • 1-dimensional (one row), 2-dimensional, and 3-dimensional arrays useful for high-density recordings.

Arrhythmias

  • (Abnormal heart rhythms) are characterized by different degrees of SA node block. -1°: Delay in node activation. -2°: Missing heartbeats (distinguished from bradycardia due to slow Heart Rate.) -3°: Impulses don't reach atria, only ventricular escape occurs.

Pacemakers

  • Use electrical impulses delivered by electrodes to regulate heart beat.
  • Types based on functionality:
    • Sequential: Coordinates with chamber activity (synchronous).
    • Asynchronous: Fires at a fixed rate.
    • Synchronous (demand): Activates when needed.
  • Components: Pulse generator (battery), wires/leads, and electrodes.
  • Types of issues: Ventricular fibrillation, erratic and uncoordinated heart cell beating.
  • Defibrillation: Sends electric energy to reset heart rhythm.

Automated External Defibrillators (AEDs)

  • Diagnose and treat treatable rhythm abnormalities.
  • Types: based on placement of electrodes (external/internal) and voltage applied. (AC/DC/Synchronized DC/Square pulse/Biphasic DC.)
  • Implantable Automatic Defibrillators (AICDs): Device to detect and correct ventricular fibrillation and tachycardia.

Plethysmography

  • Optical: Measures blood volume changes by light absorption.
  • Impedance: Measures changes in electrical impedance when blood volume changes during each heartbeat.
  • PPG wave: analyzed with derivative to detect heartbeat, hemodynamic, and arteriolar changes.
  • Variables affecting PPG: Location, Blood oxygen saturation, Blood flow rate, Skin temperature.

PPG Noise

  • PPG is subject to sudden amplitude changes.
  • Powerline Interference from electrical sources.

Design Factors

  • Instruments impacted by:
    • Signal factors (sensitivity, range, linearity)
    • Environmental factors (noise, temperature, humidity)
    • Medical factors (invasiveness, safety)
    • Economic factors (cost, availability, compatibility)
  • Design Steps: initial design, prototype testing, final design, and approval.

Regulatory Environment

  • Medical devices must meet safety and performance standards.
  • Regulatory agency in Australia: Therapeutic Goods Administration (TGA).
  • TGA Device Classifications by risk and invasiveness levels.
  • Classes: (I) lowest risk, (III) highest risk.
  • Examples of devices within each class.

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Description

This quiz explores the components and functions of medical instrumentation systems, including measurands, sensors, and signal processing techniques. It covers the essential elements such as feedback and control mechanisms critical for accurate measurements in medical applications.

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