Podcast
Questions and Answers
What is the purpose of the small flow of physiological salt solution from the bag?
What is the purpose of the small flow of physiological salt solution from the bag?
What is the pressure at which the bag is kept?
What is the pressure at which the bag is kept?
What is the function of the diaphragm in the external pressure transducer?
What is the function of the diaphragm in the external pressure transducer?
What is the rate of continuous flush for children?
What is the rate of continuous flush for children?
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What is the most commonly used site of insertion of the cannula?
What is the most commonly used site of insertion of the cannula?
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What is the purpose of the three-way stopcock in the system?
What is the purpose of the three-way stopcock in the system?
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What is the effect of the applied pressure on the resistance of strain wires 1 and 2?
What is the effect of the applied pressure on the resistance of strain wires 1 and 2?
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What is the unit of measurement for the sensitivity of a pressure transducer?
What is the unit of measurement for the sensitivity of a pressure transducer?
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What is the displacement at the center of a steel diaphragm for an applied pressure of 13 kPa?
What is the displacement at the center of a steel diaphragm for an applied pressure of 13 kPa?
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What is the ratio of change in electrical resistance when a metal strain gauge is used to detect displacement?
What is the ratio of change in electrical resistance when a metal strain gauge is used to detect displacement?
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What is the primary purpose of the direct method of pressure measurement?
What is the primary purpose of the direct method of pressure measurement?
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What is the output voltage of a bridge with metal strain gauges for 13 kPa at 5 V excitation?
What is the output voltage of a bridge with metal strain gauges for 13 kPa at 5 V excitation?
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What is the primary component detected by a sensing element in a pressure sensor?
What is the primary component detected by a sensing element in a pressure sensor?
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What additional information can be obtained from the direct measurement of blood pressure?
What additional information can be obtained from the direct measurement of blood pressure?
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What is the advantage of using disposable transducers using semiconductor piezoresistive strain gauges?
What is the advantage of using disposable transducers using semiconductor piezoresistive strain gauges?
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What is the purpose of the fast flush feature in the catheter-manometer system?
What is the purpose of the fast flush feature in the catheter-manometer system?
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What is the main purpose of the three modes of isolation in a transducer?
What is the main purpose of the three modes of isolation in a transducer?
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What is the consequence of repeated cleanings and sterilization on a pressure transducer?
What is the consequence of repeated cleanings and sterilization on a pressure transducer?
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What is the principle that utilizes metal and semiconductor elements in which electrical resistance varies with strain?
What is the principle that utilizes metal and semiconductor elements in which electrical resistance varies with strain?
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What is the estimated displacement at the center of a steel diaphragm for an applied pressure of 13 kPa (100 mmHg)?
What is the estimated displacement at the center of a steel diaphragm for an applied pressure of 13 kPa (100 mmHg)?
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What type of monitors are used to display the direct measurement of blood pressure?
What type of monitors are used to display the direct measurement of blood pressure?
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What is the fluid used to fill the catheter in the catheter-manometer system?
What is the fluid used to fill the catheter in the catheter-manometer system?
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What is the purpose of the membrane in a pre-sterilized disposable dome?
What is the purpose of the membrane in a pre-sterilized disposable dome?
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Why do physiological pressure transducers need to be sterilized before every use?
Why do physiological pressure transducers need to be sterilized before every use?
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Why is a steady flow of sterile saline passed through the catheter?
Why is a steady flow of sterile saline passed through the catheter?
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When is a Wheatstone bridge considered balanced?
When is a Wheatstone bridge considered balanced?
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What is the advantage of a pre-sterilized disposable dome in a pressure transducer?
What is the advantage of a pre-sterilized disposable dome in a pressure transducer?
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What is the strain of a metal strain gauge of 10 mm in length when used to detect displacement?
What is the strain of a metal strain gauge of 10 mm in length when used to detect displacement?
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What is the gauge factor G for metals approximately?
What is the gauge factor G for metals approximately?
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What is the output voltage of a Wheatstone bridge with metal strain gauges for 13 kPa (100 mmHg) at 5 V excitation?
What is the output voltage of a Wheatstone bridge with metal strain gauges for 13 kPa (100 mmHg) at 5 V excitation?
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Study Notes
Direct Blood Pressure Measurement
- Direct method of pressure measurement is an invasive technique requiring percutaneous cannulation
- Used when:
- Highest degree of absolute accuracy is required
- Dynamic response is necessary
- Continuous monitoring is needed
- Measuring pressure in deep regions inaccessible by indirect means
- Provides not only systolic, diastolic, and mean pressures but also:
- Visualization of the pulse contour
- Stroke volume
- Duration of systole
- Ejection time
- Other variables
Extravascular Measurement
- Also called catheter-manometer system or Fluid-filled catheter type
- Catheter is filled with saline solution, transmitting pressure to a chamber with a transducer assembly
- System must be thoroughly flushed before inserting catheter into blood vessel
- Fast flush feature is needed to fill transducer and purge air bubbles
- Steady flow of sterile saline is passed through the catheter to prevent blood clotting
Transducers
- Most pressure sensors have an elastic diaphragm and sensing element (strain gauge or variable capacitance)
- Transducer is linked directly to the patient's heart, ensuring complete safety
- Transducer must have three modes of isolation:
- External isolation of the case with a plastic sheath
- Standard internal isolation of the sensing elements from the transducer case and frame
- Additional internal isolation of the frame from the case and diaphragm in case of wire breakage
Strain Gauge Transducer
- Physiological pressure transducers need to be sterilized before each use
- Problem of repeated cleanings and sterilization is overcome by using pre-sterilized disposable dome with a built-in membrane
- Sensitivity of a pressure transducer is expressed in output voltage per unit pressure (e.g., 10 mV/mmHg)
- Strain gauge transducers are commonly used, especially disposable ones using semiconductor piezoresistive strain gauges
Wheatstone Bridge
- Wheatstone bridge is a circuit comparing unknown resistance with known values
- Output of a Wheatstone bridge is a small dc voltage
- Bridge is balanced when voltage across R2 equals voltage across R4, and output voltage is zero
- Wheatstone bridge can detect small changes in one of the resistors
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Description
Learn about the direct invasive method of blood pressure measurement, its purposes, and advantages. This method is used when high accuracy, dynamic response, and continuous monitoring are required. It provides a detailed visualization of the pressure waveform and is used in deep regions inaccessible by indirect means.
