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Questions and Answers
What occurs at the electrode-electrolyte interface when there is a concentration mismatch?
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?
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?
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?
What is represented by Ehc in the circuit model of electrode behavior?
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What is the typical amplitude range of EEG signals?
What is the typical amplitude range of EEG signals?
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What is the bandwidth range for EEG signals?
What is the bandwidth range for EEG signals?
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What is a key application of EEG monitoring?
What is a key application of EEG monitoring?
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What type of noise is a common source of error in EEG recordings?
What type of noise is a common source of error in EEG recordings?
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What is the primary role of a transducer in medical instrumentation?
What is the primary role of a transducer in medical instrumentation?
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What does EOG stand for and what does it measure?
What does EOG stand for and what does it measure?
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Distinguish between direct and indirect measurement in sensing.
Distinguish between direct and indirect measurement in sensing.
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Describe the primary purpose of EMG.
Describe the primary purpose of EMG.
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List the primary energy forms that a transducer can convert.
List the primary energy forms that a transducer can convert.
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What is the gait cycle and how is it divided?
What is the gait cycle and how is it divided?
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What are the conditions necessary for electrocution to occur?
What are the conditions necessary for electrocution to occur?
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What percentage of the gait cycle time does the stance phase occupy?
What percentage of the gait cycle time does the stance phase occupy?
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Identify one type of temperature sensor and describe its function.
Identify one type of temperature sensor and describe its function.
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List two applications of gait analysis.
List two applications of gait analysis.
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Explain the significance of calibration in medical instrumentation.
Explain the significance of calibration in medical instrumentation.
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How does the EOG relate to sleep states?
How does the EOG relate to sleep states?
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What is the threshold of death in terms of current level?
What is the threshold of death in terms of current level?
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What is the role of the vestibulo-ocular reflex as related to EOG?
What is the role of the vestibulo-ocular reflex as related to EOG?
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Describe the purpose of signal conditioning in a medical instrumentation system.
Describe the purpose of signal conditioning in a medical instrumentation system.
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Explain how EMG can be used in sports medicine.
Explain how EMG can be used in sports medicine.
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What are the three phases of the swing phase in gait analysis?
What are the three phases of the swing phase in gait analysis?
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Name two wearable systems for gait analysis.
Name two wearable systems for gait analysis.
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What is the function of an extracellular recording electrode?
What is the function of an extracellular recording electrode?
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List the signal acquisition techniques in order of spatial resolution, starting from the highest.
List the signal acquisition techniques in order of spatial resolution, starting from the highest.
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What is the role of a pacemaker in cardiac function?
What is the role of a pacemaker in cardiac function?
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Describe the first degree SA block arrhythmia.
Describe the first degree SA block arrhythmia.
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What is one disadvantage of using flexible surface electrode arrays?
What is one disadvantage of using flexible surface electrode arrays?
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Identify one medical use of accelerometry.
Identify one medical use of accelerometry.
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What factors influence the quality of a PPG signal?
What factors influence the quality of a PPG signal?
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What are the main design factors that affect the choice and design of PPG instruments?
What are the main design factors that affect the choice and design of PPG instruments?
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Describe the steps involved in the design process of a medical device.
Describe the steps involved in the design process of a medical device.
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What is the role of the Therapeutic Goods Administration in Australia regarding medical devices?
What is the role of the Therapeutic Goods Administration in Australia regarding medical devices?
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What is a major cause of sudden amplitude changes in PPG waveforms?
What is a major cause of sudden amplitude changes in PPG waveforms?
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What are the two main components of a pacemaker?
What are the two main components of a pacemaker?
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Distinguish between asynchronous and synchronous pacemakers.
Distinguish between asynchronous and synchronous pacemakers.
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What type of arrhythmia is characterized by uncoordinated heart cell beating?
What type of arrhythmia is characterized by uncoordinated heart cell beating?
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What is the primary function of an automated external defibrillator?
What is the primary function of an automated external defibrillator?
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List two types of defibrillators based on electrode placement.
List two types of defibrillators based on electrode placement.
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What type of signal processing is used in implantable automatic defibrillator systems?
What type of signal processing is used in implantable automatic defibrillator systems?
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How does photoplethysmography (PPG) differ from impedance-based plethysmography?
How does photoplethysmography (PPG) differ from impedance-based plethysmography?
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What is the purpose of analyzing the first and second derivatives of the PPG wave?
What is the purpose of analyzing the first and second derivatives of the PPG wave?
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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.