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Q. Draw both aortic root and a radial artery pressure wave forms on the same axes. Explain the differences between themAorta pressure-time curve X axis; Y axis;
Radial artery pressure-time curve X axis; Y axis;
Overview Causes of radial pulse Pressure transmission Wave & flow
Recording Occlusion & wave
Mechanism of radial waves mechanical activity electrical activity absence
Difference 1. Delay in onset
Onset & pressure rise Reason
2. Systolic peak Height Effect to systolic pressure Shape Causes
3. Presence of dicrotic notch presence Aortic curve & notch Causes
4. Shape Distorted shape Causes
4. Presence of diastolic hump presence; Causes
5. Pulse pressure Comparison Mean pressure
8. Duration Relative duration
Efffect of age on radial artery pressure contour Physiological changes in elderly
Decrease compliance of the aorta; due to aortic atheroscerosis & loss of aortic fibre Decrease myocardial performance
Changes in arterial contour Aortic curve shape
Slower upstroke than young ptn
Aortic curve height Higher peak ; due to low aortic compliance
Clinical significant Note; if this systolic peak is persistently elevated then; ptn has systolic hypertension
Summary; The low aortic compliance causes the pressure wave to travel faster and less
distorted from the contour of aortic curve Ie sama jer bentuknye
Differences with young Changes in elderly ; difference in pressure curve found in young patient The difference between aortic and radial curves in the elderly are less than found in
young ptn.
Causes of difference The differences between the waves are due to the decreased compliance which gave
rise to the steeper upstroke in the radial wave form. The higher systolic radial arterial pressure is due to reflection and summation,
tapering and faster transmission of pressure waves. Whilst damping in the radial wave causes the loss of anacrotic and dicrotic notches; whereas reflection and resonance lead to a diastolic hump on the radial wave form. In elderly patients, pulse wave may be transmitted unchanged from the ascending
aorta to the periphery because of the less compliant vessels
Short answer question Overview Aorta pressure-time curve
Radial artery pressure-time curve
Overview Causes of radial pulse Transmission of pressure wave peripherally The pressure wave travel faster than flow of blood
Recording The wave can be measured eventhough there is occlusion at distal part
Mechanism of radial waves Heart is pumping ---mechanical activity Heart is generating electricity --- has electrical activity If absence ---no radial wave
Difference 1. Delay in onset
Radial artery has---- delay in the time of onset of the initial pressure rise This is due to--- time taken to travel distally
2. Systolic peak Radial artery curve is taller Effect ---higher systolic pressure Narrower peak Due to higher velocity of higher pressure peak
3. Presence of dicrotic notch Radial aretry doesnt has diacrotic notch as aortic wave Reason--its high pressure components is dampened Dicrotic notch---which at aortic arch is the incisura due to closing of the aortic valve) becomes delayed and slurred
4. Presence of diastolic hump Radial artery pressure -time traces--has diastolic hump; this is due to reflection and resonance
5. Pulse pressure The radial pulse pressure is higher than aortic pressure, But the mean pressure ; not much difference from the mean pressure recorded
centrally peak and pulse pressures of the radial artery pressure wave to be greater than the
aortic root pressure wave.
8. Duration the radial wave pressure should show a steeper upstroke and a shorter duration than
the aortic trace
Efffect of age on radial artery pressure contour Physiological changes in elderly
Decrease compliance of the aorta; due to aortic atheroscerosis & loss of aortic fibre Decrease myocardial performance
Changes in arterial contour Slower upstroke than young ptn Higher peak ; due to low aortic compliance Note; if this systolic peak is persistently elevated then; ptn has systolic hypertension
Summary; The low aortic compliance causes the pressure wave to travel faster and less
distorted from the contour of aortic curve Ie sama jer bentuknye Changes in elderly ; difference in pressure curve found in young patient The difference between aortic and radial curves in the elderly are less than found in
young ptn.
Causes of difference The differences between the waves are due to the decreased compliance which gave
rise to the steeper upstroke in the radial wave form. The higher systolic radial arterial pressure is due to reflection and summation,
tapering and faster transmission of pressure waves. Whilst damping in the radial wave causes the loss of anacrotic and dicrotic notches; whereas reflection and resonance lead to a diastolic hump on the radial wave form. In elderly patients, pulse wave may be transmitted unchanged from the ascending
aorta to the periphery because of the less compliant vessels
Q. Write short note on measurements of end tidal CO2
Overview End tidal CO2 & capnograph Capnograph Capnograph
Capnogram CO2 & time
Capnograph Device Continous Capnogram wave form
Principal absorbtion of IR light dissimilar atom
CO2 - best at 4.3 um
Sample End tidal CO2-& --exhaled CO2 System interaction
Measurements of end tidal CO2Overview Components Tungsten wire---source of infrared light after heated to 1500-4000K Monochromatic filter----filtered only infrared to pass through Sapphire windows --not glas because glass absorbtion of infrared Sampling catheter ---either side streams or main streams Reffence chamber ---known concentration of CO2 Focus optic -----that focus the beam to a detector Detector---that display the CO2 concentration based on CO2 absorbtion
Principal Lamber law principal It= Ii e - A It= intensity of transmitted light Ii= intensity of incident light e=natural base logarithm A= product of gas absorbtion coefficients , the distance the beam travel & molar
concentration of gas
Sampling catheter side stream & main stream Side strea-location , advanatages main stream -location , advandtages
Infrared light Composition & infrared light spectrometer Tungsten wire & heat Infrared light production
Filter Filter & monochromator Filter & specific wavelength & values Filter & beam
Focus Beam & sapphire windows
Sample gas chamber & reffence chamber Emerge light from sapphire windows & sample of expired gas & refference chamber Reffence chamber & known CO2 concentration Sample chamber & measured CO2
Absorbtion IR light will be absorbed by CO2 in reffence chamber & measured chamber
Absorbtion & CO2 concentration the amount of absorbed light is proportional to CO2 concentration
Measurements The beam than pass through focussing optic and finally to detectors The detector display CO2 concentration based on degree of IR absorbtion by CO2
Normal CO2 waveform End tidal CO2 & pCO2
Phases of capnogram Phase 1
a-b---inspiratory baseline
phase 2 b-c---expiratory upstroke
phase 3 c—d---expiratory plataeu
phase 4 d-e----ispiratory downstroke
End expiration d
Start of expiration b
Start of inspiration E
Normal values d= 38 mmhg a,b,e= 0 mmhg
Capnograph oesophagus intubation Complete airway disconnection Ventilation malfunction Obstructed airway Cardiac arrest Graph
Capnograph Loss of pulmonary perfusion Pulmonary embolism Graph
Capnograph Rising body temperature Hypoventilation MH
Capnograph of soda lime exhaustion with breathing spontaneous Elevated inspiratory baseline Plateau phase limited by increased ventilation
Capnograph of soda lime exhaustion with controlled ventilation Elevated inspiratory baseline Plateau phase rise because limited ventilation
Errors COAD Sloping of capnograph Due to V/Q mistmatch
Pediatric High RR Small Vt Difficult analysis
System leak & disconnection Low traces
Nitrous oxide Nitrous oxide may absorb infrared---inaccuracy Collision broadening --the external forces that result from the interaction between CO2
that has wavelength 4.2-4.4 um & nitrous wavelength - 4.4- 4.6
Calibration In vitro with known concentration of CO2 or with calibrated sample cells
Short answer question Overview End tidal CO2 can be measured by capnograph Capnograph will display a capnogram
Capnogram Plot of concentration of carbon dioxide as function of time
Capnograph Device that continuosly record and display CO2 concentration in form of capnogram
wave form Based on principal of absorbtion of IR light by 2 dissimilar atom
End tidal CO2 can be measured by capnogram End tidal CO2---from exhaled CO2 at the end of expiration It represent ---dynamic interaction between pulmonary , cardiovascular , and metabolic
system
Measurements of end tidal CO2 End tidal CO2 is sampled by channeling CO2 via sampling catheter Sampling catheter----either side stream or main stream channel CO2 to CO2 analyser
CO2 then will be measured by IR analyser
CO2 analyser CO2 analyser ---comprised of infrared light spectrometer The system consist of IR light source that passing through filter The filter then yield the desired wavelength The beam then passing through a sample gas chamber IR light will be absorbed and the amount of absorbed light is proportional to CO2
concentration The beam than pass through focussing optic and finally to detectors The detector display CO2 concentration based on degree of IR absorbtion by CO2
Measurements of end tidal CO2Components Tungsten wire---source of infrared light after heated to 1500-4000K I Monochromatic filter----filtered only infrared to pass through I Sapphire windows --not glass because glass absorbtion of infrared I Sampling catheter ---either side streams or main streams I Reffence chamber ---known concentration of CO2 I Focus optic -----that focus the beam to a detector I Detector---that display the CO2 concentration based on CO2 absorbtion I
Principal Lamber law principal It= Ii e - A It= intensity of transmitted light Ii= intensity of incident light e=natural base logarithm A= product of gas absorbtion coefficients , the distance the beam travel & molar
concentration of gas
Sampling catheter side stream & main stream Side strea-location , advanatages main stream -location , advandtages
Infrared light Composition & infrared light spectrometer Tungsten wire & heat Infrared light production
Filter Filter & monochromator Filter & specific wavelength & values Filter & beam
Focus Beam & sapphire windows
Sample gas chamber & reffence chamber Emerge light from sapphire windows & sample of expired gas & refference chamber Reffence chamber & known CO2 concentration Sample chamber & measured CO2
Absorbtion
IR light will be absorbed by CO2 in reffence chamber & measured chamber
Absorbtion & CO2 concentration the amount of absorbed light is proportional to CO2 concentration
Measurements The beam than pass through focussing optic and finally to detectors The detector display CO2 concentration based on degree of IR absorbtion by CO2
Normal CO2 waveform Normal end expired CO2 content +/- 5% of paCO2
Phases of capnogram Phase 1
a-b---inspiratory baseline
phase 2 b-c---expiratory upstroke
phase 3 c—d---expiratory plataeu
phase 4 d-e----inspiratory downstroke
Capnograph oesophagus intubation Complete airway disconnection Ventilation malfunction Obstructed airway Cardiac arrest Graph
Capnograph Loss of pulmonary perfusion Pulmonary embolism Graph
Capnograph Rising body temperature Hypoventilation MH
Capnograph of soda lime exhaustion with breathing spontaneous Elevated inspiratory baseline Plateau phase limited by increased ventilation
Capnograph of soda lime exhaustion with controlled ventilation Elevated inspiratory baseline Plateau phase rise because limited ventilation
Errors COAD Sloping of capnograph Due to V/Q mistmatch
Pediatric High RR Small Vt Difficult analysis
System leak & disconnection Low traces
Nitrous oxide Nitrous oxide may absorb infrared---inaccuracy
Collision broadening --the external forces that result from the interaction between CO2 that has wavelength 4.2-4.4 um & nitrous wavelength - 4.4- 4.6
Calibration In vitro with known concentration of CO2 or with calibrated sample cells
Factor affect capnographInhalational Agents
Inhalational agents do not affect CO2 measurement The low concentrations of halogenated anaesthetic agents used during anaesthesia
absorb IR energy at different wave lengths (around 3.3 milli microns) their interference is not considered to be important
Atmospheric pressure Increases in atmospheric pressure result in an increase in the PETCO2 values by
increasing number of IR absorbing molecules and increasing intermolecular forces the CO2 read high minimize error by Calibrating with a known concentration of CO2 as partial pressure
at the site of measurement
Nitrous oxide nitrous oxide absorbs IR (IR absorption spectra of N20 = 4.5 µm whereas C02 = 4.3
µm), the presence of N20 therefore can give falsely high C02 readings. This problem can be eliminated by using a narrow band IR filter that only transmits
the the wavelength most strongly absorbed by C02 (about 4.3 µm). Another problem relates to N2O concerns the interaction between N20 molecules and C02 molecules.
This produces a "collision broadening effect" that affects the sensitivity of the IR analyzer and causes an apparent increase in C02 reading
Q. Describe how the partial pressure of oxygen in a blood sample is measured using a Clark electrode
Overview
partial pressure of oxygen
blood gas analysers & O2 tension & clark electrode
polarographic electrode.
Clark electrode
electrode & oxygen & platinum surface
Principal
reaction:
Component of clark electrode
Overview
Electrode --cathode & anode
Cathode
platinum cathode & glass rod
Solution
Anode
silver/silver chloride anode
Solution
Temperature
electrode is kept at 37 degrees.
Accuracy
has accuracy of +/- 2 mmHg
Calibration
calibration occurs via use of standardised gas mixtures
solution/electrolyte
NaCl
KCL
Function
2 electrodes are held within this solution
voltage
voltage of 700 mv
polarising voltage is supplied to the electrodes
ammeter reading the electrical potenatial generated
O2 permeable membrane Components
whole cell & plastic membrane,
Character To gases To liquids or solids
Function Electrode & blood prevent deposition Oxygen equilibrium
Diagram
Mechanism of action
AT ANODE:
Reaction
Product
Equation
AT CATHODE:
O2 & electrons & water
Equation
Process
eletron & cathode Process & electric potential Effect of process
Problems & limitations
Electrode
O2 electrode must be clean/ uncontaminated.
Electrode wrapper
intact.
Sample
Anaerobically
heparinised.
Sampling time
Prompt
Reason
Short answer question
Overview
Partial pressure: pressure a gas would exert if it alone occupied a space.
blood gas analysers allow measurement of the O2 tension in blood using the clark electrode (
also called polarographic electrode.
Clark electrode
electrode
measures oxygen
on a catalytic platinum surface
using the reaction: O2 + 2 e- + 2 H2O → H2O2 + 2 OH-
Component of clark electrode
electrode
platinum cathode ----- kept in glass rod
silver/silver chloride anode----- kept in AgCl gel.
electrode is kept at 37 degrees.
has accuracy of +/- 2 mmHg
calibration occurs via use of standardised gas mixtures
solution/electrolyte
sodium chloride eletrolyte solution ---
KCL is alternative ---
2 electrodes are held within this solution
voltage
voltage of 700 mv---- polarising voltage is supplied to the electrodes
ammeter reading the electyrical potenatial generated
O2 permeable membrane ------ whole cell is wrapped in a plastic membrane, permeable to gases but not liquids or solids separate the electrode from blood ----- prevent deposition of protein ---- allow oxygen tension in the blood to equilibrate with electrolyte solution
Diagram
Mechanism of action
AT ANODE:
Ag reacts with KCl creating AgCl and free electrons
Ag + Cl -------> AgCl + e-
AT CATHODE:
O2 combines with electrons and water (
O2 + 4e +2H2O makes 4(OH)-
Process
eletron ----taken up at the cathode-platinum the current is generated that proportional to oxygen tension
Problems & limitations
O2 electrode must be clean/ uncontaminated.
plastic membrane must be intact.
blood sample must be taken anaerobically and heparinised.
analysis must be prompt as O2 falls with time, especially at room temp due to O2 consumption by cells, ice storage of samle helps to slow this).
Q. Briefly explain the principles of Doppler ultrasound used to measure cardiac output.[edit]
Examiner's Report[edit]2005
52 % of candidates passed this question.
Important points:
Nature of ultrasound waves and working frequencies Piezoelectric effect Doppler effect Doppler equation relating velocity and Doppler shift in frequency Components of the Doppler equation, particularly the incident angle Cardiac output measurement Measurement of flow from cross sectional area and velocity Integrated flow over time to give stroke volume Heart rate Advantages/disadvantages
The most common mistake was to equate velocity or a single flow rate with cardiac output; not accounting for the pulsatile nature of cardiac output.
[edit]1998
Only thirty-three percent (33%) of candidates achieved a pass standard in this question. Many candidates were obviously taken by surprise by the question and had no knowledge of even basic Doppler principles. However, of those who passed, a number wrote excellent answers. The better papers included a discussion of:
The phenomenon of Doppler Shift (frequency shift and velocity of target) The measurement of Aortic Red Cell velocity The measurement of Aortic cross sectional area (M mode echocardiography) The relationship between velocity (mean vs. peak of profile), cross sectional area,
and flow (cardiac output) The effect of the angle of incidence of ultrasound beam on velocity measurement
(cosine q) The relative accuracy of the measurement
One answer included a correct formula of target velocity (knowing frequency shift, speed of sound in tissue, frequency of ultrasound wave, and the angle between ultrasound and target).
A surprising number of candidates chose not to answer the question at all and wrote nothing, or chose to answer their own question (eg. "Compare and contrast the different methods of measuring cardiac output" or "write notes on clinical use of transoesophageal echocardiography")
Q.Briefly describe the potential causes of a difference between measured end-tidal and arterial partial pressure of carbon dioxide.
Overview the difference is attributed into 1. patient factors 2. measurement error
Patient factors overview patient factor are: increase alveolar dead space, delayed alveolar emptying , smoker, pulmonary embolism
Graph
alveolar dead space Overview alveolar dead space is volume of inspired gas that passed through anatomical dead
space but not participate in gas exchange
Mechanism that causes difference the failure of gas exchange result in reduction of transfer of CO2 from arterial blood to alveolar resulting in the show arterial to end expiratory pCO2 gradient
Delayed alveolar emptying Overview delayed alveolar emptying slow rise of alveolar air may cause low expired CO2 detected by capnograph
Causes may be due to air trapping in airway secondary to airway obstruction
smoker smoking may cause increase in dead space – resulting lung dysfunction it may cause arterial to end expiratory pCO2 gradient
increasing age elderly patient show arterial to end expiratory pCO2 gradient
increased anatomical dead space Overview anatomical dead space is volume of gas exhaled before CO2 concentration rises to its
alveolar plateau
Causes of anatomical dead space increasing antomical dead space for example ---with; neck extended and jaw protruded ,
bronchodilator agent such as inhlational agent – result in increase anatomical dead space
Physiological effect of dead space that may cause a difference between measured end-tidal and arterial partial pressure of
carbon dioxide.
lung pathology pulmonary embolism may cause failure of transfer of CO2 from arterial to alveoli
Measurement error Overview CO2 in end- tidal is measured by infrared analyser/capnograph to measure CO2 levels
continously. CO2 in arterial blood is measured by CO2 sensitive electrode via arterial sample
Causes of errors any measurement error involving this equipment may result in difference between
measured end-tidal and arterial partial pressure of carbon dioxide.
measurement error of end tidal CO2Machine error
Inadequate calibration of infrared sensor
Sampling errors
Inadequate tidal volume
Blockage of sampling line
sample error
Air entrainment into sampling line (leaks)
Measurement error of arterial CO2Machine errors
Not calibrated to pressure and temperature
Electrode errors
Damage to Severinghaus electrode - damage to semi-permeable membrane
Sampling errors
Delay of 2-3 minutes while CO2 diffuses for measurement
Delay of sample being measured
not placed on ice
Sample errors
Air bubble in blood sample
Excess heparin (acid) resulting in reduced measure PCO2
Venous sample taken instead of arterial sample
Q. Draw an expiratory flow volume curve for a forced expiration from total lung capacity. Describe its characteristics in people with normal lungs,as well as those
with obstructive and restrictive lung disease. Briefly explain the physiological mechanisms involved in the concept of flow limitation
Overview
Normal. Overview
Inspiratory limb of loop is symmetric and convex. Expiratory limb is linear.
Curve Y Axis; flow in l/sec X axis; volume in l Plots -- TLC, FRC, RV Shape ---slightly triangular
Values of flowOverview
Maximal inspiratory flow at 50% of forced vital capacity (MIF 50%FVC) is greater than maxi-mal expiratory flow at 50% FVC
you see
Causes of maximal inspiratory flow (MEF 50%FVC) because dynamic compression of the air-ways occurs during exhalation. Therefore ---it restrict the airflow during expiration
Effort dependent and effort independent
Effort dependentOverview Location
Effort dependent is the airflow from maximal inspiration (TLC) to expiratory volume of half of the lung volume,
Relationship
in which the greater the effort the higher the flow rate
Mechanism
When subject exhaled from maximal inspiration --->higher lung volume
the greater the effort to exhaled the air ---the higher the flow rate
Therefore airflow ---the flow rate is effort dependent.
Slope of PV loop
Greater the effort---greater positive intrapleural pressures ----result in higher flow rates.
Submaximal effort produced lower flow rates and flattened peak of flow volume curve.
Effort independent flow
Overview
Effort independent flow is the expiration of air from mid lung volume to the lowest possible lung volume or RV,
Relatioship
in which the flow rate doesn't increased despite greater effort of exhalation
Mechanism
As expiration progresses, mid lung volumes are reached
there is a subsequent progressive reduction in flow rate which continues through low lung volume until full expiration complete -----(lung in RV).
Slope of effort independent
Slope generated following peak flow rate until RV is the plateau.
At mid to low lung volumes, flow rates gradually decline as air is expelled.
It is not possible to increase flow rates even with greater intrathroacic pressures.
Flow is therefore effort independent at this point.
Causes of effort independent pat
Effort independent part of the curve is a result of dynamic compression of the airways.
From graph
The effort independent part includes most of the descending part of expiration curve
Dynamic airway compression
During a forceful expiration, the intrathoracic or pleural pressure (Pit) rises
The intrathoracic pressure causes the alveolar pressure (Palv) to exceed the downstream pressure at the airway openings (PB).
As flow resistance dissipates the driving energy along the bronchial tree, the driving pressure of the cartilaginous bronchi falls towards zero at the mouth
At a certain point the forces that expand the airway equal the forces that tend to collapse.
This is the equal pressure point.
Beyond the equal pressure point the driving pressure falls below the external pressure, and the bronchi are compressed .
At this point the person cannot voluntarily increase the rate of expiratory airflow, because increased effort also increases the external pressure.
This phenomenon is called dynamic airway compression with airway collapse.
Factor affect dynamic airway compression Airway resistance
Lung volume
Flow-volume loop in severe obstructive disease
Overview
In obstructive diseases, the flow rate is very low in relation to lung volume,
Example Asthma
effect to volume residual volume is above normal due to air trapping the VC below normal
Shape of flow-volume curve scooped in (concave)appearance The patient inspires maximally and starts a maximal expiration, However ,due to the high airway resistance, the flow rate become very low in relation
to lung volume
Mechanism The airway resistance is high because of the inflammed airways that are obstructed
by secretion and smooth muscle contraction. The number of airways are reduced as is the pulmonary elastic recoil with loss of
alveolar walls and traction causing the airways to collapse.
Flow volume curve in severe restrictive lung disease Overview
Restrictive lung disease is characterized by small lung volumes
Effect to lung volume TLC is small, all volumes are often proportionally decreased. RV is below the normal The TLC is below normal
Effect to airflow velocity The airflow velocity and relative forced expiratory volume in 1 s is typically normal. One way or the other, the normal expansion of the lungs is restricted or the
pulmonary compliance is decreased In restrictive diseases, the maximum flow rate is reduced, as is the total volume
expired. The flow is abnormally high in the latter part of expiration because of increased
recoil.
Shape Scooped out Convex
Q. Briefly explain how oximetry can be used to estimate the partial pressure of oxygen in a blood sample
Overview
Partial pressure of oxygen & definition Oxymetry & paO2
Oxymetry & Spectrophotometric Source & radiation & beam & sample & absorbtion of radiation & extent of absorbtion Extent of absorbtion & concentration of gas
Application of laws Extent of absorbation of radition & concentration of gas
Principle of application Beer lambert law----It = Ii ´e- DCa where, It = the intensity of the transmitted light Ii = intensity of the incident light D = the distance through the medium the light passed C = the concentration of the solute a = the extinction coefficient of the solute
Extinction coefficients the extinction coefficient & specific solute & specific wavelength of light
Components of pulse oximetry Light emiting diode 2 LED One LED transmit red light with wavelength of 660 nm, other transmit infrared light with wavelength of 940 nm.
Photocell
Photocell or photodiode absorbed the extent of light absorbences The light absorbences produce voltage that depends on light absorbtion Light absorbtion depend on oxygen saturation
Miscroprocessor Calculate ratio of absorbtion by pulsatile tissue
Note The point at which the absorbences for the two forms of hemoglobin are identical =
isobestic points The isobestic point only dependent on hemoglobin concentration
Mechanism of pulse oximetry Light transmission Infrared & light red transmitted through tissue , to venous blood , then finally pulsatile
arteriole
Light absorbtion Light beam onto red cell Red cell---oxyhemoglobin & deoxyhemoglobin Difference absorbtion & difference wavelength therefore from the ratio of the absorption of the red and infrared light the
oxy/deoxyhemoglobin ratio can be calculated.
Measured variables Pulsatile tissue & non-pulsatile tissue
Pulsatile tissue absorbtion of red light by deoxyhemoglobin absorbtion of red light by oxyhemoglobin Absorbtion of infrared light by deoxyhemoglobin Absorbtion of infrared light by oxyhemoglobin
Non-pulsatile tissue absorbtion of red light by deoxyhemoglobin absorbtion of red light by oxyhemoglobin Absorbtion of infrared light by deoxyhemoglobin Absorbtion of infrared light by oxyhemoglobin
Miscroprocessor comparison of the absorbances at these wavelength -----calculate oxygen saturation
Method Ratio of absorbtion of AC 660 of pulsatile arterial deoxyhemoglobin / DC 660 non
pulsatile venous deoxyhemoglobin / AC 940 Ratio of absorbtion of AC 940 of pulsatile arterial oxyhemoglobin / AC 940 non pulsatile
oxyhemoglobin SaO then measured by logarithm
Isobestic point point at which the absorbances for the two form of hemoglobin are identical isobestic point---only depend on hemoglobin concentration
Calibration
Short answer question Overview Partial pressure of oxygen & definition Oxymetry & paO2
Oxymetry & Spectrophotometric Source & radiation & beam & sample & absorbtion of radiation & extent of absorbtion Extent of absorbtion & concentration of gas
Application of laws Extent of absorbation of radition & concentration of gas
Principle of application Beer lambert law----It = Ii ´e- DCa where, It = the intensity of the transmitted light Ii = intensity of the incident light D = the distance through the medium the light passed
C = the concentration of the solute a = the extinction coefficient of the solute
Extinction coefficients the extinction coefficient & specific solute & specific wavelength of light
Components of pulse oximetry Light emiting diode 2 LED One LED transmit red light with wavelength of 660 nm, other transmit infrared light with wavelength of 940 nm.
Photocell
Photocell or photodiode absorbed the extent of light absorbences The light absorbences produce voltage that depends on light absorbtion Light absorbtion depend on oxygen saturation
Miscroprocessor Calculate ratio of absorbtion by pulsatile tissue
Note The point at which the absorbences for the two forms of hemoglobin are identical =
isobestic points The isobestic point only dependent on hemoglobin concentration
Mechanism of pulse oximetry Light transmission Infrared & light red transmitted through tissue , to venous blood , then finally pulsatile
arteriole
Light absorbtion Light beam onto red cell Red cell---oxyhemoglobin & deoxyhemoglobin Difference absorbtion & difference wavelength therefore from the ratio of the absorption of the red and infrared light the
oxy/deoxyhemoglobin ratio can be calculated.
Measured variables Pulsatile tissue & non-pulsatile tissue
Pulsatile tissue absorbtion of red light by deoxyhemoglobin absorbtion of red light by oxyhemoglobin Absorbtion of infrared light by deoxyhemoglobin Absorbtion of infrared light by oxyhemoglobin
Non-pulsatile tissue absorbtion of red light by deoxyhemoglobin absorbtion of red light by oxyhemoglobin Absorbtion of infrared light by deoxyhemoglobin Absorbtion of infrared light by oxyhemoglobin
Miscroprocessor
comparison of the absorbances at these wavelength -----calculate oxygen saturation
Method Ratio of absorbtion of AC 660 of pulsatile arterial deoxyhemoglobin / DC 660 non
pulsatile venous deoxyhemoglobin / AC 940 Ratio of absorbtion of AC 940 of pulsatile arterial oxyhemoglobin / AC 940 non pulsatile
oxyhemoglobin SaO then measured by logarithm
Isobestic point point at which the absorbances for the two form of hemoglobin are identical isobestic point---only depend on hemoglobin concentration
Calibration
Error
nail
coloured nail varnish, especially blue varnish absorn at 660
affect Sat , false reduction
dye
idocyanine, methylene blue in thyroid surgery, fluorescein causes decrease in saturation
fluorescein no significant effect
effect last 5-10 minutes
methaemoglobin
erroneoly read high despite having low sat
absorb same red light at 660
also absorb infrared light at 940
Carboxyhemoglobin
erroneoly read high despite having low sat
smaller absorbtion of red light at 660
also absorb infrared light at 940
but the ratio of absorbances is preserved
HbF
same absorbtion spectrum as HbA
no effect on pulse oximetry
HbS
no significant effect
Anemia
may be smaller underestimation
Polycythemia
no effect
Other sources of error
Excessive movement & malpositioning
fluoresecent ambient light
high airway pressure, hypoperfusion , vasoconstriction, valsalva decrease venous return
Short answer questionSpectrophotometric Definition Technique of measurement that involve shining the radiation through a sample and
determined the quantity of radiation absorbed The wavelength of radition that is absorbed by the studied compound is chosen
Principle of action Two laws that becoame the basic of study:1. Beer’s law2. Bouguer law or Lambert’s law
Beer’s law : The absorbtion of radiation by a given thickness of a solution of a given concentration
is the same as that of a solution of a given concentration id the same as that of twice the thickness of solution of half the concentration
Lambert law Each layer of equal thickness absorbs an equal fraction which passes through it
Application of laws The absorbation of radition by studied compound is increases when the concentration
increases At low concentration, the absorbtion is proportional to the concentration
Principle of application spectrophotometry was first used to determine the [Hb] of blood in the 1930's, by
application of the Lambert-Beer Law where, Ii = the incident light
It = the transmitted light
D = the distance through the medium
C = the concentration of the solute
a = the extinction coefficient of the solute
the extinction coefficient is specific for a given solute at a given wavelength of light therefore, for each wavelength of light used an independent Lambert-Beer equation can
be written, and if the number of equations = the number of solute, then the
concentration for each one can be solved , Lambert- Beer equation , It = Ii ´e- DCa
Oximeter Oximeter : the light that consists of various wavelength is transmitted through
hemolyzed blood sample Photocell absorbed the extent of light absorbences so that the oxygen saturation can be
calculated Latest model use various wavelength of light to give the direct reading of saturation and
also the total hemoglobin
Pulse oximeter A pulse oximeter is a medical device that indirectly measures the amount of oxygen in
a patient's blood and changes in blood volume in the skin, a photoplethysmograph. Oximeter : the light that consists of various wavelength is transmitted through
hemolyzed blood sample Photocell or photodiode absorbed the extent of light absorbences so that the oxygen
saturation can be calculated
Note The point at which the absorbences for the two forms of hemoglobin are identical =
isobestic points The isobestic point only dependent on hemoglobin concentration
Principle of action of pulse oximeter Typically it has a pair of small light-emitting diodes facing a photodiode through a
translucent part of the patient's body, usually a fingertip or an earlobe. One LED is red, with wavelength of 660 nm, and the other is infrared 940 nm. Absorption at these wavelengths differs significantly between oxyhemoglobin and its
deoxygenated form, therefore from the ratio of the absorption of the red and infrared light the
oxy/deoxyhemoglobin ratio can be calculated. comparison of the absorbances at these wavelength -----calculate oxygen saturation
Isobestic point point at which the absorbances for the two form of hemoglobin are identical isobestic point---only depend on hemoglobin concentration
Pulse oximeter
Principles of Pulse Oximetry Technology:
The principle of pulse oximetry is based on the red and infrared light absorption characteristics of oxygenated and deoxygenated hemoglobin.
Oxygenated hemoglobin absorbs more infrared light and allows more red light to pass through.
Deoxygenated (or reduced) hemoglobin absorbs more red light and allows more infrared light to pass through.
Red light is in the 600-750 nm wavelength light band.
Infrared light is in the 850-1000 nm wavelength light band.
Q.Explain how cardiac output is measured by thermodilution technique.
Overview
Definition of CO
Definition & formula
Measurements of CO
Two technique
principal
Indicators dilution technique
Overview
Definition & invasive
Principle
stewart hamilton & fick principal
Injection
Setting
Cold water
Thermistor
Measurements of CO
CO & AUC.
Stewart hamilton equation
Limits of indicator dilution technique
Flow
1. Assumes constant flow.
Heart
1. Assumes structurally normal heart (eg. normal valves)
Measured parameter
1. Measures global function; no information on regional abnormalities.
2. When measuring preload it cannot differentiate between a change in LV Compliance and a change in LVEDV.
Technique
1. Risk of injury on insertion / flotation of PAC.
2. Minimal evidence of improved mortality with use of PAC to guide therapy.
Fick Principle:
Simple version of Stewart Hamilton Equation:
The Fick principle
Fick relationship:
Q = M / (V - A)
Where Q is the volume of blood flowing through an organ in a minute,
M the number of moles of a substance added to the blood by an organ in one minute,
and V and A are the venous and arterial concentrations of that substance.
This principle can be used to measure the blood flow through any organ that adds substances to, or removes substances from, the blood.
CO & pulmonary blood flow
The heart does not do either of these but the
CO equals the pulmonary blood flow,
lungs add oxygen to the blood and remove carbon dioxide from it.
The concentration of the oxygen in the blood in the pulmonary veins is 200 ml/L
Concentration of oxygen in pulmonary artery is 150 ml/L,
so each litre of blood going through the lungs takes up 50 ml.
At rest, the blood takes up 250 ml/min of oxygen from the lungs and this 250 ml must be carried away in 50 ml portions;
therefore, the CO must be 250/50 or 5 L/min.
Dilution techniques
Dye dilution:
Methods
amount of dye & injection
Calculations of concentration
Characteristic of dye
Toxicity
Halflife
Alternative
Technique
Injection site
Measurements
Measurements
Electrode & radial arterial cannula.
Formula and calculations
Plot
CO &(AUC)
Graph
Y axis; dye concentration
X axis; time
Thermodilution
Overview
Amount , injection , site
Measurements
Measurements
A plot
Stewart-Hamilton equation.
CO=( initial blood temperature - injectate temp ) x computation costant x injectate volume / integral of temperature changes over time
Graph
Y axis; temperature decrease as per voltage
X axis; time
Assumption of the technique
1. Mixture
2. Loss
3. flow
Formula
The amount of indicator (n) is related to its mean concentration (c),
cardiac output (Q)
and the time for which it is detected (t2 - t1).
Advanatages
Patients
Safe
Doctors
Rapid
Frequent
Disadvantage
Doctors
accuracy
Reliability
cost
Overestimation
Patients
cvs
Temperature
valve
Overview
CO---volume of blood pumped each minutes by each ventricle
CO--product of stroke volume & heart rate
Measurements of CO
CO---can be measured indirectly by dye dilution technique & thermodilution technique
Both technique uses Fick principal
Indicators dilution technique
Overview
Invasive indirect technique to measure cardiac output
Principle
Uses stewart hamilton indicator dilution technique that is derived from fick principal
It applies bolus
Setting
Cold water injected down Pulmonary Artery Catheter.
Thermistor on the end measures temperature change.
Measurements of CO
Flow rate (CO) is the Amount of Indicator injected divided by the AUC.
Stewart hamilton equation
Limits of indicator dilution technique
Flow
1. Assumes constant flow.
Heart
1. Assumes structurally normal heart (eg. normal valves)
Measured parameter
1. Measures global function; no information on regional abnormalities.
2. When measuring preload it cannot differentiate between a change in LV Compliance and
a change in LVEDV.
Technique
1. Risk of injury on insertion / flotation of PAC.
2. Minimal evidence of improved mortality with use of PAC to guide therapy.
Alternative Techniques
1. MRI with velocity encoded phase contrast
2. Dye Dilution (indiocyanine)
3. Doppler
4. PICCO
Fick Principle:
Simple version of Stewart Hamilton Equation:
The Fick principle
Fick relationship:
Q = M / (V - A)
Where Q is the volume of blood flowing through an organ in a minute,
M the number of moles of a substance added to the blood by an organ in one minute,
and V and A are the venous and arterial concentrations of that substance.
This principle can be used to measure the blood flow through any organ that adds substances to, or removes substances from, the blood.
CO & pulmonary blood flow
The heart does not do either of these but the
CO equals the pulmonary blood flow,
lungs add oxygen to the blood and remove carbon dioxide from it.
The concentration of the oxygen in the blood in the pulmonary veins is 200 ml/L
Concentration of oxygen in pulmonary artery is 150 ml/L,
so each litre of blood going through the lungs takes up 50 ml.
At rest, the blood takes up 250 ml/min of oxygen from the lungs and this 250 ml must be carried away in 50 ml portions;
therefore, the CO must be 250/50 or 5 L/min.
Dilution techniques
Dye dilution:
Methods
A known amount of dye ie 10 mls of 25 mg idiocyanine green is injected into venous circulation in RA
its concentration is measured peripherally after one complete circulation ---30-40 second
The mean concentration of the dye is calculated
Characteristic of dye
Indocyanine green is suitable due to its low toxicity and short half-life.
Lithium has also been used as an alternative to indocyanine green.
Technique
It is injected via a central venous catheter
measured by a lithium-sensitive electrode
Measurements
Theidiocyanine green is measured by lithium-sensitive electrode
lithium-sensitive electrode incorporated into the radial arterial cannula.
Formula and calculations
Plot the curve of idiocyanine green concentration versus time
CO is calculated from the injected dose, divided by the area under the curve (AUC) and its duration.
Graph
Y axis; dye concentration
X axis; time
Thermodilution
Overview
5-10 ml cold saline injected through the proximal injection port of a pulmonary artery catheter.
Temperature changes are measured by a distal thermistor.
Measurements
A plot of temperature change against time gives a similar curve to the dye curve (but without the second peak).
Calculation of CO is achieved using the Stewart-Hamilton equation.
CO=( initial blood temperature - injectate temp ) x computation costant x injectate volume / integral of temperature changes over time
Graph
Y axis; temperature decrease as per voltage
X axis; time
Assumption of the technique
Application of this equation assumes three major conditions;
1. complete mixing of blood and indicator,
2. no loss of indicator between place of injection and place of detection and
3. constant blood flow.
The errors made are primarily related to the violation of these conditions.
Formula
The amount of indicator (n) is related to its mean concentration (c),
cardiac output (Q)
and the time for which it is detected (t2 - t1).
Advantages
Patients
Safe
Doctors
Rapid
Frequent
Disadvantage
Doctors
Not as accurate as fick and indicators dilution technique
Unreliable if > 10% variations
Expensive
Overestimation of CO---highest at end expiration
Patients
Arrythmia if rapid injection
Hypothermia
Tricuspid regurgitation
Q. Briefly describe the measurement of blood pressure using an automated oscillometric non-invasive blood pressure monitor. Briefly outline the problems of this kind of monitor. Overview
LV contraction blood ejection vascular system Pulsation systolic pressure diastolic pressure Pulse pressure
Automated oscillometry Definition of automated Definition of oscillometry DINAMAP
Site of measurement Relative to artery Arm
Size of cuff bladder length ---80% of width 40% of arm circumfererence L:W
Inflation of pressure Inflation Oscillation Cuff pressure Transducer next Cuff pressure hold Cuff release Pulsation Next Cuff pressure repeated
Blood pressure systolic pressure point diastolic pressure point Mean Arterial Pressure = Diastolic Arterial Pressure + 1/3 pulse pressure
Relaibllity
most reliable pressure measurement
Error
Devices factors
Size
Calibration
Patients factors
Obesity
CO
Rhythm
Short answer question Overview
Rhythmic LV contraction>>>blood ejection enter>>>vascular system>>> pulsatile arterial pressure
Peak pressure during systolic --------systolic blood pressure Trough pressure during diastolic pressure----------diastolic blood pressure Pulse pressure: difference between systolic & diastolic pressure Mean arterial pressure: systolic pressure + 2 diastolic pressure X 1/3 Mean arterial pressure : diastolic pressure + 1/3( pulse pressure)
Measurements of arterial blood pressure ABP depend sampling site: As pulse move peripherally>>>> wave reflection distort the pressure
waveform>>>exaggeration of arterial blood pressure
Principle of measurement based on oscilllometry eq; DINAMAP= device for indirect non-invasive automatic mean arterial pressure
Oscilometry Def : technique of measuring BP by measuring oscillation produced by arterial
pulsation
Technique:Site of measurement
measure above artery upper arm over brachial artery
Size of cuff bladder length ---80% of width , 40% of arm circumfererence length to width ratio----1:2
Inflation of pressure Cuff inflated above systolic >>> small oscillation produced Cuff pressure-----monitored by machine pressure transducer Cuff pressure---decreased by small amount ----then held for a period of time Cuff released >>>pulsation transmitted to entire cuff----the oscillation /pulsation
detected by transducer Then cuff further decerased by small amount of pressure Process repeated as above
Measurement of oscillation Use automated blood pressure>>> to monitor changes of oscillation amplitude Then : microprocessor derives / calculate the values by algorithm when samll oscillation in pressure rise significantly---the baseline pressure---measure
as systolic as cuff pressure continue to decrease in series of small steps-----machine determine
size of oscillation above baseline pressure Oscilation initially increase---then decrease the baseline pressure at the point when the oscillation are maximum size---is mean
arterial pressure
Blood pressure systolic pressure ---- when samll oscillation in pressure rise significantly---the baseline
pressure mean aretrial pressure ---- the baseline pressure at the point when the oscillation are
maximum diastolic pressure calculated as variations of Mean Arterial Pressure = Diastolic
Arterial Pressure + 1/3 pulse pressure
Relaibllity
most reliable pressure measurement
error
inappropriate cuff size, ----cuff too small or too large, more error with cuff to small irregular heart rhythms (particularly atrial fibrillation), ---- bllod pressure varies with
every contraction----no reliable determination of pressure patient movement including shivering, low output states, inaccurate calibration. obese----large arm circumference with short upper arm length