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Q. Draw both aortic root and a radial artery pressure wave forms on the same axes. Explain the differences between them Aorta 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;

Clinical Measurements SAQ

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Page 1: Clinical Measurements SAQ

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

Page 2: Clinical Measurements SAQ

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

Page 3: Clinical Measurements SAQ

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

Page 4: Clinical Measurements SAQ

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

Page 5: Clinical Measurements SAQ

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

Page 6: Clinical Measurements SAQ

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

Page 7: Clinical Measurements SAQ

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

Page 8: Clinical Measurements SAQ

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

Page 9: Clinical Measurements SAQ

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

Page 10: Clinical Measurements SAQ

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

Page 11: Clinical Measurements SAQ

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

Page 12: Clinical Measurements SAQ

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

Page 13: Clinical Measurements SAQ

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

Page 14: Clinical Measurements SAQ

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

Page 15: Clinical Measurements SAQ

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).

Page 16: Clinical Measurements SAQ

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")

Page 17: Clinical Measurements SAQ

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 ,

Page 18: Clinical Measurements SAQ

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

Page 19: Clinical Measurements SAQ

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

Page 20: Clinical Measurements SAQ

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

Page 21: Clinical Measurements SAQ

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

Page 22: Clinical Measurements SAQ

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

Page 23: Clinical Measurements SAQ

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.

Page 24: Clinical Measurements SAQ

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

Page 25: Clinical Measurements SAQ

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

Page 26: Clinical Measurements SAQ

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

Page 27: Clinical Measurements SAQ

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

Page 28: Clinical Measurements SAQ

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

Page 29: Clinical Measurements SAQ

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

Page 30: Clinical Measurements SAQ

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

Page 31: Clinical Measurements SAQ

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

Page 32: Clinical Measurements SAQ

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.

Page 33: Clinical Measurements SAQ

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:

Page 34: Clinical Measurements SAQ

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.

Page 35: Clinical Measurements SAQ

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

Page 36: Clinical Measurements SAQ

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

Page 37: Clinical Measurements SAQ

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

Page 38: Clinical Measurements SAQ

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.

Page 39: Clinical Measurements SAQ

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

Page 40: Clinical Measurements SAQ

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

Page 41: Clinical Measurements SAQ

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

Page 42: Clinical Measurements SAQ

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