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Edit Comment Close Premium member Presentation Transcript Introduction to Flow & Pressure Transducers : Introduction to Flow & Pressure Transducers Measuring Flow & Pressure Flow Transducers Vitalograph Abnormal Expiratory Patterns Pressure Transducers Waveforms, resonance & damping What is resonance & damping? Why does it matter? Pulse waveforms, ECGs and EEGs Flow & Pressure : Flow & Pressure What is “flow” : What is “flow” Volume of a fluid passing a point in a given time (l/min) What is “pressure”? : What is “pressure”? Force per unit area Pascal (1N force over 1 square meter) (1 Newton = force giving 1kg acceleration of 1m/s/s) What is a “transducer”? : What is a “transducer”? device that converts energy from one form to another. (usually to electricity for monitoring) What flows to we need commonly measure?Why? : What flows to we need commonly measure?Why? Measuring Flow : Measuring Flow Gas flow Precise delivery of Gases Rotameter Monitoring respiratory volumes (breathing circuits) Pneumotachograph Pulmonary function tests Peak flow meters Vitalograph Liquids flow IV infusion devices (drip counters) The 2 types of flow….. : The 2 types of flow….. …..and their important differences Laminar or Turbulent Flow : Laminar or Turbulent Flow Laminar flow requires lower pressures for the same flow rate Slide 11: p x Pressure x Radius4 8 x Viscosity x Tube Length Hagen--Poiseuille Equation (Laminar Flow) Transition to Turbulent Flow : Transition to Turbulent Flow When fluid reaches a critical velocity Reynolds number >2000 Turbulent flow not directly proportional to pressure Velocity (V), Density (p), Tube Diameter (d), Viscosity (n) How do we measure flow? : How do we measure flow? Volume/time How to measure flow : How to measure flow Directly Measure VOLUME in unit time Vitalograph Indirectly Measure another property that changes in proportion to flow Pressure drop (pneumotachograph/bobbin rotameter) Mechanical movement (spirometer/peak flow meter) Heat transfer/cooling (anemometer) Vitalograph spirometryVolume/time = FEV1 FVC : Vitalograph spirometryVolume/time = FEV1 FVC Normal Spirometry : Normal Spirometry Normal Spirometry : Normal Spirometry Restrictive Defects : Restrictive Defects Obstructive Defects : Obstructive Defects Pneumotachograph : Pneumotachograph Pressure drops across constant resistance Laminar flow Pressure change = flow Accuracy FX: Condensation Gas temp Gas viscosity (LF) ….. Has heater Bobbin Rotameter(variable orifice flow meter) : Bobbin Rotameter(variable orifice flow meter) Keeps pressure across bobbin constant despite increasing flow Bigger orifice, less resistance Gas specific Laminar bottom (viscosity) Turbulent top (density) FX by: Sticking, static, wrong gas Back flow Vane meters Wrights Respirometer : Vane meters Wrights Respirometer Gas kinetic energy related to velocity Spinning vane Measure volume (you add time) FX by: Low flow (friction) under reads High flow (momentum) over reads Vane metersPeak Flow Meter : Vane metersPeak Flow Meter Variable orifice Vane moves allowing more gas to escape Maximum flow rate only Final position = peak flow rate Asthma reduced (500l/min) Hot wire Anemometer : Hot wire Anemometer Gas cools heated wire Cooling = flow rate Limited frequency response Why do we need to measure pressures? : Why do we need to measure pressures? Measuring Pressure : Measuring Pressure Gas Pressure cylinders, anaesthetic machines, breathing circuits Liquids CVP, IABP …..usually given as “gauge pressure” not “absolute pressure” In the UK we use a lot of units! : In the UK we use a lot of units! 1 atmosphere = 1 bar (gas cylinders) 100kPa (blood gas, EtCo2) 14.5 psi (cylinders, car tyres) 750mmHg (blood pressure) 1020cmH20 (CVP) Types : Types Aneroid gauge (mechanical) Manometer Piezoresistive strain gauge (electrical) Aneroid (fluid-less) Gauge : Aneroid (fluid-less) Gauge Bourdon Gauge (gas cylinders) High pressures >1bar (too high for fluid column!) Simple, robust, no power needed No good for very low pressures (<5cmH20) Manometer : Manometer Mercury mmHg (high pressures) Water cmH20 (low pressures) Alcohol Simple but bulky No calibration needed Piezoresistive Strain Gauge (the most commonly used transducer) : Piezoresistive Strain Gauge (the most commonly used transducer) Diaphragm deformed by pressure Semiconductor material changes resistance Measured by a Wheatstone bridge Signal amplified and processed High or low pressures Electrical signal for display Needs power Gets electrical interference Wheatstone Bridge : Wheatstone Bridge Rx is the unknown resistance R1, R2, R3 known resistances Resistance of R2 is adjustable If (R2 / R1) = (Rx / R3) = 0 voltage R2 is varied until this condition is reached Current direction indicates whether R2 is too high or too low. Arterial Blood Pressure : Arterial Blood Pressure To be accurate system must: : To be accurate system must: Be calibrated/zero balanced Be at right resonance…… Have the right amount of damping….. Resonance & Damping are sources of error! : Resonance & Damping are sources of error! Resonance (& Tacoma Narrows Bridge) : Resonance (& Tacoma Narrows Bridge) Resonance : Resonance Frequency response should allow good reproduction of arterial signal Monitoring systems have a natural (resonant) frequency at which they resonate and amplify the signal If driving force frequency = resonant frequency …..then signal over-amplified amplified & distorted (systolic too high, diastolic too low) Tubing chosen so natural freq not encountered in normal range of frequencies (10x higher than max) Raised with short stiff catheter Lowered into into “clinical” range by extra connections etc Damping : Damping Some energy is removed from the driving oscillations Energy is taken OUT of the system Reduces amplitude size and stop over/undershoots “Damping factor” – tendency of system to resist oscillations Under-damped : Under-damped Over-estimation of pressure change Overestimates SBP, underestimates DBP Optimal Damping : Optimal Damping Fastest response without excessive oscillation (cf critical damping D=1) Critical v Optimal Damping : Critical v Optimal Damping Critical damping - after flushing system there is NO overshoot or undershoot (D=1)….but response too slow! Optimal Damping - system settles with a couple of small oscillations - faster response, but you accept a small degree of error (D=0.7) Over damped : Over damped Slow to respond (phase shift) Overestimates DBP Underestimates SBP Causes: Air bubbles, blood clots Soft diaphragm/soft tubing Multiple connectors Testing for damping : Testing for damping Fast flush technique One or two oscillations Waveforms : Waveforms Waveform Monitoring in Anaesthesia : Waveform Monitoring in Anaesthesia Repetitive waveforms over time Cardiovascular (ECG, IABP, PAP, CVP) Neurological (EEG, nerve conduction, ICP) Respiratory (rate, depth, pattern) Ventilatory (gas flow, pressure) Fourier Analysis : Fourier Analysis Wavefoms into sine waves Slowest “fundamental” frequency & harmonics For analysis & monitoring Monitor must be able to reproduce high freq harmonics for accuracy ECG 0.5-80Hz, EEG 1-60Hz You do not have the permission to view this presentation. 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Flow & Pressure aSGuest17572 Download Post to : URL : Related Presentations : Share Add to Flag Embed Email Send to Blogs and Networks Add to Channel Uploaded from authorPOINT lite Insert YouTube videos in PowerPont slides with aS Desktop Copy embed code: (To copy code, click on the text box) Embed: URL: Thumbnail: WordPress Embed Customize Embed The presentation is successfully added In Your Favorites. Views: 863 Category: Science & Tech.. License: All Rights Reserved Like it (0) Dislike it (1) Added: April 27, 2009 This Presentation is Public Favorites: 0 Presentation Description No description available. Comments Posting comment... By: pradeepbawane (32 month(s) ago) this presentation is valuable for me as am the lecturer can u plz share with me with regards pradeep Saving..... Post Reply Close Saving..... Edit Comment Close Premium member Presentation Transcript Introduction to Flow & Pressure Transducers : Introduction to Flow & Pressure Transducers Measuring Flow & Pressure Flow Transducers Vitalograph Abnormal Expiratory Patterns Pressure Transducers Waveforms, resonance & damping What is resonance & damping? Why does it matter? Pulse waveforms, ECGs and EEGs Flow & Pressure : Flow & Pressure What is “flow” : What is “flow” Volume of a fluid passing a point in a given time (l/min) What is “pressure”? : What is “pressure”? Force per unit area Pascal (1N force over 1 square meter) (1 Newton = force giving 1kg acceleration of 1m/s/s) What is a “transducer”? : What is a “transducer”? device that converts energy from one form to another. (usually to electricity for monitoring) What flows to we need commonly measure?Why? : What flows to we need commonly measure?Why? Measuring Flow : Measuring Flow Gas flow Precise delivery of Gases Rotameter Monitoring respiratory volumes (breathing circuits) Pneumotachograph Pulmonary function tests Peak flow meters Vitalograph Liquids flow IV infusion devices (drip counters) The 2 types of flow….. : The 2 types of flow….. …..and their important differences Laminar or Turbulent Flow : Laminar or Turbulent Flow Laminar flow requires lower pressures for the same flow rate Slide 11: p x Pressure x Radius4 8 x Viscosity x Tube Length Hagen--Poiseuille Equation (Laminar Flow) Transition to Turbulent Flow : Transition to Turbulent Flow When fluid reaches a critical velocity Reynolds number >2000 Turbulent flow not directly proportional to pressure Velocity (V), Density (p), Tube Diameter (d), Viscosity (n) How do we measure flow? : How do we measure flow? Volume/time How to measure flow : How to measure flow Directly Measure VOLUME in unit time Vitalograph Indirectly Measure another property that changes in proportion to flow Pressure drop (pneumotachograph/bobbin rotameter) Mechanical movement (spirometer/peak flow meter) Heat transfer/cooling (anemometer) Vitalograph spirometryVolume/time = FEV1 FVC : Vitalograph spirometryVolume/time = FEV1 FVC Normal Spirometry : Normal Spirometry Normal Spirometry : Normal Spirometry Restrictive Defects : Restrictive Defects Obstructive Defects : Obstructive Defects Pneumotachograph : Pneumotachograph Pressure drops across constant resistance Laminar flow Pressure change = flow Accuracy FX: Condensation Gas temp Gas viscosity (LF) ….. Has heater Bobbin Rotameter(variable orifice flow meter) : Bobbin Rotameter(variable orifice flow meter) Keeps pressure across bobbin constant despite increasing flow Bigger orifice, less resistance Gas specific Laminar bottom (viscosity) Turbulent top (density) FX by: Sticking, static, wrong gas Back flow Vane meters Wrights Respirometer : Vane meters Wrights Respirometer Gas kinetic energy related to velocity Spinning vane Measure volume (you add time) FX by: Low flow (friction) under reads High flow (momentum) over reads Vane metersPeak Flow Meter : Vane metersPeak Flow Meter Variable orifice Vane moves allowing more gas to escape Maximum flow rate only Final position = peak flow rate Asthma reduced (500l/min) Hot wire Anemometer : Hot wire Anemometer Gas cools heated wire Cooling = flow rate Limited frequency response Why do we need to measure pressures? : Why do we need to measure pressures? Measuring Pressure : Measuring Pressure Gas Pressure cylinders, anaesthetic machines, breathing circuits Liquids CVP, IABP …..usually given as “gauge pressure” not “absolute pressure” In the UK we use a lot of units! : In the UK we use a lot of units! 1 atmosphere = 1 bar (gas cylinders) 100kPa (blood gas, EtCo2) 14.5 psi (cylinders, car tyres) 750mmHg (blood pressure) 1020cmH20 (CVP) Types : Types Aneroid gauge (mechanical) Manometer Piezoresistive strain gauge (electrical) Aneroid (fluid-less) Gauge : Aneroid (fluid-less) Gauge Bourdon Gauge (gas cylinders) High pressures >1bar (too high for fluid column!) Simple, robust, no power needed No good for very low pressures (<5cmH20) Manometer : Manometer Mercury mmHg (high pressures) Water cmH20 (low pressures) Alcohol Simple but bulky No calibration needed Piezoresistive Strain Gauge (the most commonly used transducer) : Piezoresistive Strain Gauge (the most commonly used transducer) Diaphragm deformed by pressure Semiconductor material changes resistance Measured by a Wheatstone bridge Signal amplified and processed High or low pressures Electrical signal for display Needs power Gets electrical interference Wheatstone Bridge : Wheatstone Bridge Rx is the unknown resistance R1, R2, R3 known resistances Resistance of R2 is adjustable If (R2 / R1) = (Rx / R3) = 0 voltage R2 is varied until this condition is reached Current direction indicates whether R2 is too high or too low. Arterial Blood Pressure : Arterial Blood Pressure To be accurate system must: : To be accurate system must: Be calibrated/zero balanced Be at right resonance…… Have the right amount of damping….. Resonance & Damping are sources of error! : Resonance & Damping are sources of error! Resonance (& Tacoma Narrows Bridge) : Resonance (& Tacoma Narrows Bridge) Resonance : Resonance Frequency response should allow good reproduction of arterial signal Monitoring systems have a natural (resonant) frequency at which they resonate and amplify the signal If driving force frequency = resonant frequency …..then signal over-amplified amplified & distorted (systolic too high, diastolic too low) Tubing chosen so natural freq not encountered in normal range of frequencies (10x higher than max) Raised with short stiff catheter Lowered into into “clinical” range by extra connections etc Damping : Damping Some energy is removed from the driving oscillations Energy is taken OUT of the system Reduces amplitude size and stop over/undershoots “Damping factor” – tendency of system to resist oscillations Under-damped : Under-damped Over-estimation of pressure change Overestimates SBP, underestimates DBP Optimal Damping : Optimal Damping Fastest response without excessive oscillation (cf critical damping D=1) Critical v Optimal Damping : Critical v Optimal Damping Critical damping - after flushing system there is NO overshoot or undershoot (D=1)….but response too slow! Optimal Damping - system settles with a couple of small oscillations - faster response, but you accept a small degree of error (D=0.7) Over damped : Over damped Slow to respond (phase shift) Overestimates DBP Underestimates SBP Causes: Air bubbles, blood clots Soft diaphragm/soft tubing Multiple connectors Testing for damping : Testing for damping Fast flush technique One or two oscillations Waveforms : Waveforms Waveform Monitoring in Anaesthesia : Waveform Monitoring in Anaesthesia Repetitive waveforms over time Cardiovascular (ECG, IABP, PAP, CVP) Neurological (EEG, nerve conduction, ICP) Respiratory (rate, depth, pattern) Ventilatory (gas flow, pressure) Fourier Analysis : Fourier Analysis Wavefoms into sine waves Slowest “fundamental” frequency & harmonics For analysis & monitoring Monitor must be able to reproduce high freq harmonics for accuracy ECG 0.5-80Hz, EEG 1-60Hz