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PHYSICS PHYSICS MCQsMCQs
Cyprian MendoncaCyprian Mendonca
TopicsTopics
�� Measurement of blood gasesMeasurement of blood gases
�� Measurement of gas flowMeasurement of gas flow
�� Monitoring ECGMonitoring ECG
�� Monitoring & Measurement of oxygenMonitoring & Measurement of oxygen
�� Measurement of blood pressureMeasurement of blood pressure
�� Agent monitoringAgent monitoring
�� SeveringhausSeveringhaus electrodeelectrode
�� Clark electrode Clark electrode (blood: gas factor)(blood: gas factor)
�� Mass spectrometryMass spectrometry
�� Fuel cellFuel cell
�� Infrared analyserInfrared analyser
FTTTFFTTTF
Mass spectrometryMass spectrometry
Mass SpectrometryMass Spectrometry
O2CO2 Enflurane
Rapid response time
Multiple gas analysis
Expensive
too bulky
Angle of deflection
depends on
charge mass ratio
Charge/mass
Charge/mass
�� Blood gas analyser directly measures Blood gas analyser directly measures
Pa OPa O22, PaCO, PaCO22 and pHand pH using using
specific electrodes .specific electrodes .
�� Membrane permeable to OMembrane permeable to O22, CO, CO2, 2, HH++
Bicarbonate Bicarbonate
� 2 electrodes
� Reference electrode : Ag /Agcl
� Measuring electrode: pH glass
� Electrolyte: NaHCO3, Kcl
Mesh -HCO3-
H+ glass
electrodes
CO2+H2O H2CO3 H+ +HCO3-
CO2 permeable teflon membrane
H+
H+
H+ sensitive glass
KclBuffer
Ag/Agcl or calomel reference electrode
Reference electrode
Measuring
electrode
Ag/AgCl
leaky membrane
Voltage change in the measuring electrode
V
CO2 pH
Ref Elect Ag/AgCl Ag/Agcl
Hg/Hgcl
Measuring
Electrode
pH glass pH glass
Electrolyte Kcl,
NaHCO3
Kcl
� Excess heparin in the sample lowers the pH value
� Sampled blood can be stored at room temp for up to one hour
� pH is usually calculated using Siggard-Anderson nomogram
� CO2 electrodes are maintained at room temperature
� CO2 electrodes have a response time of 20 secs
TFFFFTFFFF
Response time 2Response time 2--3 minutes3 minutes
1 1 kPakPa = 30 minutes= 30 minutes
2ml = 80 units of heparin
� has CO2 sensitive glass
� uses sodium bicarbonate as electrolyte
� is an indirect method of measuring carbon dioxide tension
� is accurate to within 1mmHg
� is temperature-dependent
FTTTTFTTTTIndirect: 0.01 unit of pH change per 0.1 kPa COIndirect: 0.01 unit of pH change per 0.1 kPa CO22
�� Fuel cellFuel cell
�� Clark electrodeClark electrode
�� Paramagnetic oxygen anlaysersParamagnetic oxygen anlaysers
Gold cathode
Finite shelf-life=1year
calibration
self generated voltage
No power supply
slow response
Pb + 2OH- PbO + 2e- + 2H2O
KOHLead anode
�� FiOFiO22 reading is not affectedreading is not affected
�� Life span of cell is affectedLife span of cell is affected
(N(N22O reacts with lead anode)O reacts with lead anode)
polarising voltage 0.7 V
Platinum cathode
KCl
Ag/AgCl anode
�� AnodeAnode
Ag + Cl = AgCl + Ag + Cl = AgCl + ee
�� CathodeCathode
O2 + 2H2O + O2 + 2H2O + 4e4e = 4OH= 4OH
�� ElectolyteElectolyte
NaCl + OH = NaOH + ClNaCl + OH = NaOH + Cl
Electrons donated at anode, consumed at Electrons donated at anode, consumed at
cathodecathode
Polarographic-platinum, Agcl
Fuel cell Clark
Anode Lead Ag/Agcl
Cathode gold platinum
Electrolyte KOH Kcl, Nacl
�� Has a Gold cathodeHas a Gold cathode
�� Has a platinum anode Has a platinum anode (lead)(lead)
�� Uses sodium hydroxide as the Uses sodium hydroxide as the electrolyte solution electrolyte solution (KOH)(KOH)
�� Require a voltage of 6Require a voltage of 6--7 volts applied 7 volts applied across the electrodes across the electrodes (0.7 V for clark)(0.7 V for clark)
�� Is affected by the presence of NIs affected by the presence of N22OO
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�� aa. . InfraredInfrared analyseranalyser
�� b. Raman spectroscopyb. Raman spectroscopy
�� c. Mass spectrometryc. Mass spectrometry
�� d. Refractometerd. Refractometer
�� e. Quartz crystale. Quartz crystal
�� TTTTTTTTFF
�� pHpH
�� Standard bicarbonate : Standard bicarbonate : SiggardSiggard--Anderson Anderson
nomogramnomogram
�� Carboxy haemoglobinCarboxy haemoglobin
�� Oxyhaemoglobin saturation:Oxyhaemoglobin saturation: ODC
�� Base excessBase excess
FTFTTFTFTT
a)measures Oxygen concentration a)measures Oxygen concentration
b)is the classical method of calibrating b)is the classical method of calibrating
vaporisers vaporisers
c)is affected by water vapour c)is affected by water vapour
d)does not require prior calibration d)does not require prior calibration
e)is affected by temperaturee)is affected by temperature
FTTTTFTTTTAll affected by water vapour except fuel cellAll affected by water vapour except fuel cell
�� When sine waves of same frequency, amplitude When sine waves of same frequency, amplitude
and phase are added, resulting sine wave will and phase are added, resulting sine wave will
have greater amplitude. If two sine waves are have greater amplitude. If two sine waves are
180180oo out of phase, the resulting sine wave will out of phase, the resulting sine wave will
have zero amplitude and appears as straight have zero amplitude and appears as straight
line. Addition of sine waves in a variable degree line. Addition of sine waves in a variable degree
of out of phase will result in respective change in of out of phase will result in respective change in
the amplitude. the amplitude.
�� In a refractometer increased amplitude gives In a refractometer increased amplitude gives
rise to bright fringe, reduced amplitude gives rise rise to bright fringe, reduced amplitude gives rise
to dark fringe. There are two chambers. One is to dark fringe. There are two chambers. One is
reference chamber and a sample chamber. The reference chamber and a sample chamber. The
change in the phase of sine waves in the sample change in the phase of sine waves in the sample
chamber and resultant displacement of fringe chamber and resultant displacement of fringe
pattern is dependent on the type and pattern is dependent on the type and
concentration of the anaesthetic agent. concentration of the anaesthetic agent.
�� Is based on the principle that O2 is repelled by the Is based on the principle that O2 is repelled by the magnetic fieldmagnetic field
�� Is incorporated into the blood gas analyserIs incorporated into the blood gas analyser
�� can provide breath to breath measurementcan provide breath to breath measurement
�� Can measure CO2Can measure CO2
�� Null deflection paramagnetic analyser has the Null deflection paramagnetic analyser has the advantage of containing no moving partsadvantage of containing no moving parts
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N2 N2
% O2
sample
*Calibration
N2 N2sample
Differential pressure transducer
Pulsed magnetic field
Sample gas with more oxygen attracted to the magnetic field
& produces pressure difference across the transducer
Sample gas
Reference gas
�� 4%4%
�� 21%21%
�� 5%5%
�� 7%7%
�� 0.3%0.3%
FFTFFFFTFF
40 mm Hg x 0.13 = 5.3 kPa40 mm Hg x 0.13 = 5.3 kPa
5.3 5.3 –– 0.3 to 0.8 =4.5 to 5 kPa0.3 to 0.8 =4.5 to 5 kPa
� Has a standard paper speed of 50mm/s.
� Has a Normal axis between +30o to -90o
� Has a maximal Q-Tc interval of 0.48s..
� Has a QRS duration of 0.08-0.12s.
� May have an inverted T wave in aVR
FFFTTFFFTT
PR =0.12PR =0.12-- 0.2, QT < 0.44, 0.2, QT < 0.44, --3030o o to +90to +90oo
P= 0.1s, 2.5 mm,P= 0.1s, 2.5 mm,
a. applies to both electromagnetic radiation and a. applies to both electromagnetic radiation and
soundsound
b. changes the b. changes the velocityvelocity of reflected soundof reflected sound
c. is based on the piezoc. is based on the piezo--electric properties of electric properties of
crystalscrystals
d. shows the shift to lower frequency if the source d. shows the shift to lower frequency if the source
is moving away from the receiveris moving away from the receiver
e. can indicate the velocity of red ce. can indicate the velocity of red cellsells
TFFTTTFFTT
�� A lower signal to noise ratio is better than a A lower signal to noise ratio is better than a
higher ratio higher ratio
�� Diagnostic mode in the ECG monitor has a Diagnostic mode in the ECG monitor has a
frequency response of 0.5 to 40 Hzfrequency response of 0.5 to 40 Hz
�� CM5 configuration is ideal for detecting CM5 configuration is ideal for detecting
arrhythmiaarrhythmia
�� Signal to Noise ratio can be improved by using Signal to Noise ratio can be improved by using
filters.filters.
�� Differential amplifier can reduce the electrical Differential amplifier can reduce the electrical
interferenceinterference
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12. Concerning ECG Monitoring12. Concerning ECG Monitoring
�� A A highhigh signal to noise ratio is better than a signal to noise ratio is better than a
higher ratio higher ratio
�� MonitoringMonitoring mode in the ECG monitor has a mode in the ECG monitor has a
frequency response of 0.5 to 40 Hzfrequency response of 0.5 to 40 Hz
�� Diagnostic mode 0.Diagnostic mode 0.005 to 100 Hz.5 to 100 Hz.
�� CM5 configuration is ideal for detecting CM5 configuration is ideal for detecting
ischaemiaischaemia
�� Signal to Noise ratio can be improved by filtersSignal to Noise ratio can be improved by filters
Monitoring mode : 0.5 - 40 Hz
Diagnostic mode: 0.05 -100Hz : ST segment, QRS not distorted
Right arm = red = C Manubrium
Clavicle =Neutral = green
Left arm = yellow = V5 position
Select lead 1
Amplifier amplifies the signal before it is displayed on the Amplifier amplifies the signal before it is displayed on the
monitor.monitor.
A differential amplifier measures the difference between the A differential amplifier measures the difference between the
potential from two sources. Any interference which is potential from two sources. Any interference which is
common to the input terminal such as 50Hz mains common to the input terminal such as 50Hz mains
frequency is eliminated. This rejection of common input frequency is eliminated. This rejection of common input
frequency is known as common mode rejection. frequency is known as common mode rejection.
�� Nail varnishNail varnish
�� MethyleneMethylene BlueBlue
�� Tricuspid incompetenceTricuspid incompetence
�� MethaemoglobinMethaemoglobin
�� CarboxyhaemoglobinCarboxyhaemoglobin
TTTTTTTTTT
�� accuracy : +/accuracy : +/--2%, >70%: +/2%, >70%: +/--3% 503% 50--70%70%
Hypoperfusion
Ambient light
Fluorescent, xenon
Movements
Diathermy
External dyes, Nail varnish (black/green)
Abnormal haemoglobins
HbMet, HbCO, Indocyanine green, Methy. blue
No effectHbF, HbS, Bilurubin, anaemia
Acrylic nails.
�� a. Nitrous oxidea. Nitrous oxide
b. Oxygenb. Oxygen
c. Heliumc. Helium
d. Entonoxd. Entonox
e. Medical aire. Medical air
�� T FFFFT FFFF
�� a. Nitrous oxide: 36.5 a. Nitrous oxide: 36.5 ooCC
b. Oxygen: b. Oxygen: --118.4118.4 ooC C
c. Helium:c. Helium:
d. Entonox: d. Entonox: --77 ooC C
e. Medical air: e. Medical air: --140140 ooCC
15. Regarding measurement of Gas flow
Examples of Constant Orifice/Variable Pressure
devices include
�� PneumotachographPneumotachograph
�� Peak flow meterPeak flow meter
�� RotameterRotameter
�� PitotPitot tubetube
� Wright respirometer
TFFTFTFFTF
Gas flow & Volume measurementGas flow & Volume measurement
�� Pneumotachograph Pneumotachograph
fixed orifice, variable pressure drop, fixed orifice, variable pressure drop, Q = P/RQ = P/R-- Fleisch PneumotachographFleisch Pneumotachograph
-- Screen PneumotachographScreen Pneumotachograph
-- Pitot tube PneumotachographPitot tube Pneumotachograph
-- Hot wire PneumotachographHot wire Pneumotachograph
�� Peak flow meterPeak flow meter
variable orifice, fixed pressure drop flow metervariable orifice, fixed pressure drop flow meter
Gas flow & Volume measurementGas flow & Volume measurement
Q = P/RQ = P/R
�� Direct measurement of Direct measurement of volumevolume
Spirometer & Wright RespirometerSpirometer & Wright Respirometer
�� Variable orificeVariable orifice-- constant pressure constant pressure dropdrop
Rotameter, Peak flowmeterRotameter, Peak flowmeter
�� Fixed orificeFixed orifice-- variable pressure variable pressure dropdrop
Pneumotachograph, Pitot tube.Pneumotachograph, Pitot tube.
16. The concentration of isoflurane in a
breathing system can be measured using
�� a. Mass spectrometera. Mass spectrometer
�� b. Paramagnetic analyserb. Paramagnetic analyser
�� c. Refractometerc. Refractometer
�� d. Infrared analyserd. Infrared analyser
�� e. Ultrasonic analyser : e. Ultrasonic analyser : velocity of soundvelocity of sound
�� T FTTTT FTTT
�� The composition of isothermal binaryThe composition of isothermal binary--gas gas
mixtures can be determined by measuring mixtures can be determined by measuring
the velocity of sound in the gasthe velocity of sound in the gas
17. Flow can be measured by
� The Fick principle
� High frequency sound wave reflection
� Change in temperature of a hot wire
� Pressure drop across a constriction
� Venturi effect
TTTTTTTTTT
Fick principle:Fick principle:
blood flow to any organ = Qx / [Axblood flow to any organ = Qx / [Ax--Vx]Vx]Inhaled nitrous oxide is used.Inhaled nitrous oxide is used.
�� Qx: amount of substance removed by the Qx: amount of substance removed by the
organorgan
�� Ax: arterial conc.Ax: arterial conc.
�� Vx: venous concentrationVx: venous concentration
18. Flow meters in anaesthetic machines18. Flow meters in anaesthetic machines
�� N2O can be used in an O2 flow meter without N2O can be used in an O2 flow meter without changes in calibrationchanges in calibration
�� Are variable orifice variable pressure devicesAre variable orifice variable pressure devices
�� Uses a straight tube and a bobbinUses a straight tube and a bobbin
�� Have a linear scaleHave a linear scale
� Both Laminar and turbulent flows are encountered
FFFFTFFFFT
N2O, CO2 = MW =44, density similar =1.997 mg/cm3 at N2O, CO2 = MW =44, density similar =1.997 mg/cm3 at 00ooCC
Viscosity =1488 poise at 27Viscosity =1488 poise at 27ooC, CO2 ?C, CO2 ?LV HDLV HD
19. 19. RotaRota meters in anaesthetic machinesmeters in anaesthetic machines
�� Have an accuracy of about 2%Have an accuracy of about 2%
�� Are calibrated at 37Are calibrated at 37ooC and a pressure of 101.3 C and a pressure of 101.3 kPakPa
�� Reading should be taken from the bottom of Reading should be taken from the bottom of the bobbinthe bobbin
�� Are gas specificAre gas specific
�� At low flows, viscosity play important role At low flows, viscosity play important role
TFFTTTFFTT
LV, HDLV, HD
Flow meters vs AltitudeFlow meters vs Altitude
�� Q =PrQ =Pr44/nl = /nl = √√P/P/ρρll
HighHigh pressure = false pressure = false highhigh reading, over reading, over --
readsreads
Low pressure = false low reading, underLow pressure = false low reading, under--
readsreads
Back pressure ~ underBack pressure ~ under--readsreads
LV, HDLV, HD
20. Distribution of ventilation is 20. Distribution of ventilation is
measured bymeasured by
a.a. Helium dilution techniqueHelium dilution technique
b.b. Body Body plethysmographyplethysmography
c.c. Nitrogen wash out Nitrogen wash out
d.d. radioactive xenonradioactive xenon
e. 100% oxygen. 100% oxygen
FFFTFFFFTF
2020
�� Radioactive albumin : PerfusionRadioactive albumin : Perfusion
�� Radioactive gas (xenon)Radioactive gas (xenon)
21. Wrights respirometer may give a low
reading when
a) high tidal volume is used a) high tidal volume is used (over(over--reads)reads)
b) FiO2 = 0.3b) FiO2 = 0.3
c) Nitrous oxide is usedc) Nitrous oxide is usedd) Humidification is used
e) e) mechanical ventilation is used mechanical ventilation is used (over(over--reads reads
due to high peak flow at the beginning)due to high peak flow at the beginning)
UnderUnder--reads at low flows. Overreads at low flows. Over--reads at high flowreads at high flow
�� WrightWright’’s respirometer is a turbine s respirometer is a turbine
flowmeter flowmeter
�� A series of tangential slits that cause A series of tangential slits that cause
circular motion of the gas flow that circular motion of the gas flow that
produces rotation around the vaneproduces rotation around the vane
�� The vane does not rotate when the flow is The vane does not rotate when the flow is
reversedreversed
�� The composition of gas used does not The composition of gas used does not
influence its performance influence its performance
�� UnderUnder--reads at low flow and over reads at reads at low flow and over reads at
high flowhigh flow
22. Pulse 22. Pulse oximeteroximeter probes probes
[a] [a] Emit near infraEmit near infra--red light.red light.
[b] Once calibrated, do not need re[b] Once calibrated, do not need re--
calibrating.calibrating.
[c] Can cause heating of contact tissues.[c] Can cause heating of contact tissues.
[d] Are damaged by mild detergents[d] Are damaged by mild detergents..
[e] Are rendered inaccurate by 70% isopropyl [e] Are rendered inaccurate by 70% isopropyl
alcoholalcohol
F T T F FF T T F F
23. 23. PneumotachographPneumotachograph
a. measures laminar flowa. measures laminar flowb. measures the pressure differenceb. measures the pressure differencec. is more accurate if heated to a c. is more accurate if heated to a constant temperatureconstant temperatured. can be used to measure the volumed. can be used to measure the volumee. it shows a linear response only e. it shows a linear response only within the calibration rangewithin the calibration range
T T TT TT TT TT
Measures Flow, volume = flow /time
24. Regarding Temperature and 24. Regarding Temperature and
HeatHeat
1.1. Absolute zero is Absolute zero is --273K273K
2. Boiling point of water is +373K
3. Water freezes at +273K
4.4. SI unit of temperature is calorieSI unit of temperature is calorie
5.5. Daltons law states that Volume varies Daltons law states that Volume varies directly with temperaturedirectly with temperature
FTTFFFTTFF
24. Regarding Temperature and 24. Regarding Temperature and
HeatHeat
1.1. Absolute zero Absolute zero is is --273 C or 0 K273 C or 0 K
2. Boiling point of water is + 373K
3. Water freezes at +273K
4.4. SI unit of temperature is SI unit of temperature is KelvinKelvin
5.5. Daltons law states that Volume varies Daltons law states that Volume varies directly with temperaturedirectly with temperature
00ooC = 273 KC = 273 K
Gas lawsGas laws
�� Daltons: In a mixture of gases, pressure Daltons: In a mixture of gases, pressure
exerted by each gas is same as that which exerted by each gas is same as that which
it would exert if it alone occupied the it would exert if it alone occupied the
container.container.
Absolute ZeroAbsolute Zero 0K 0K --273C273C --459F459F
Freezing pointFreezing point 273K 273K 0C0C 32F32F
H2OH2O
Boiling pointBoiling point 373K 100C373K 100C 212F212F
K=C+273K=C+273
C=5/9(FC=5/9(F--32)32)
F=9/5(C+32)F=9/5(C+32)
25, Invasive blood pressure25, Invasive blood pressure
a. is higher in dorsalis pedis artery as compared a. is higher in dorsalis pedis artery as compared
toto brachial artery in supine positionbrachial artery in supine position
�� b. Requires a system pressurised to 300kPa b. Requires a system pressurised to 300kPa
(mm Hg)(mm Hg)
c. records a higher systolic pressure as c. records a higher systolic pressure as
compared to NIBPcompared to NIBP
d. is unreliable in hypertensive patientd. is unreliable in hypertensive patient
e. Records a more accurate mean arterial e. Records a more accurate mean arterial
pressure as compared to NIBPpressure as compared to NIBP
Factors affecting dampingFactors affecting damping
�� fn = fn = √√DD22./pLC./pLC
fn = natural frequency , fn = natural frequency ,
D = diameter of catheter, D = diameter of catheter,
pp = density, = density,
L =length, L =length,
C = compliance.C = compliance.
Resonance and dampingResonance and damping
�� Inertial forces : massInertial forces : mass
�� Elastic forces: springElastic forces: spring
�� Friction forces: mediumFriction forces: medium
�� FluidFluid
�� DiaphragmDiaphragm
�� Viscous effect of fluidViscous effect of fluid
�� Mass Mass ––spring systemspring system
•fn = √D2./pLC
Resonance and damping
Square wave test D2 /D1 = 5 /10 =0.5
Amplitude ratio = D. coeff
1 cycle,; fn = speed / 1 cycle (mm)
D2 D1
300 mmHg
The loss of pressure in the bag, compliant
tubing, stopcocks, length >120 cm, kinking
of the cannula, blood clots and air bubblesStiff tube, diaphragm
�� Critical damping= no oscillations, no Critical damping= no oscillations, no overshoot.overshoot.
�� UnderUnder--damped more than 3 cycles before damped more than 3 cycles before reaching zero.reaching zero.
�� Amplitude ratio of 0.1 = optimum damping Amplitude ratio of 0.1 = optimum damping = damping coefficient 0.6 = damping coefficient 0.6 --0.7, 0.640.7, 0.64
�� fn = fn = √√DD22./pLC./pLC
�� increased compliance reduces natural increased compliance reduces natural frequencyfrequency
�� a) a) 7.5 mm Hg is equivalent to 10 cm H7.5 mm Hg is equivalent to 10 cm H22OO
�� bb) 1 ) 1 kPakPa is equal to a pressure of 7.5 mm is equal to a pressure of 7.5 mm
HgHg
�� cc) 1 bar is equal to 15 psi) 1 bar is equal to 15 psi
�� dd) A mercury barometer used to measure ) A mercury barometer used to measure
atmospheric pressure is sealed with a atmospheric pressure is sealed with a
vacuum above the surface of the liquid vacuum above the surface of the liquid
�� ee) Aneroid gauges do not contain liquid) Aneroid gauges do not contain liquid
Atmospheric pressureAtmospheric pressure
1 bar = 15 psi =1000cm H1 bar = 15 psi =1000cm H220 =750 mm Hg0 =750 mm Hg
=100kPa=100kPa
1 psi =6.89 1 psi =6.89 kPakPa
�� a. is dependent on the viscosity of the fluida. is dependent on the viscosity of the fluid
�� b. doubles if the radius of the cannula is doubledb. doubles if the radius of the cannula is doubled
�� c. doubles if the length of the cannula is halvedc. doubles if the length of the cannula is halved
�� d. is inversely proportional to the length of the d. is inversely proportional to the length of the cannulacannula
�� e. doubles if the pressure is doubled.e. doubles if the pressure is doubled.
�� TFTTTTFTTT
�� Q is proportional to the rQ is proportional to the r44
�� Q =P Q =P rr44/nl/nl
28. With regard to accidental 28. With regard to accidental
electrocutionelectrocution
(a) The risk of ventricular fibrillation increases with (a) The risk of ventricular fibrillation increases with increasing current frequency.increasing current frequency.
(b) (b) The risk of ventricular fibrillation is greater with The risk of ventricular fibrillation is greater with alternating current.alternating current.
(c) The use of battery operated equipment avoids the (c) The use of battery operated equipment avoids the risk of ventricular fibrillation.risk of ventricular fibrillation.
(d) The risks of electrocution is reduced by (d) The risks of electrocution is reduced by earthingearthingthe patient.the patient.
(e) All electrical equipment in the operating theatre (e) All electrical equipment in the operating theatre should be earthed (should be earthed (battery operated).battery operated).
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29.29.
�� a) The blood gas results are normal to this a) The blood gas results are normal to this
patientpatient
�� b) An echocardiogram would be useful.b) An echocardiogram would be useful.
�� c) A ventilation perfusion scan would be helpful c) A ventilation perfusion scan would be helpful
in diagnosisin diagnosis
�� d) An intrapulmonary shunt is accountable for d) An intrapulmonary shunt is accountable for
these findingsthese findings
�� e) An increased dead space is accountable for e) An increased dead space is accountable for
these findings.these findings.
�� FTTFTFTTFT
30.With respect to statistics30.With respect to statistics
� Null hypothesis states that there is no real difference between two sets of data
� Rejection of the null hypothesis leads to acceptance of the alternate hypothesis
�� Beta error occurs if the null hypothesis is Beta error occurs if the null hypothesis is wrongly rejected.wrongly rejected.
�� Alpha error states that the null hypothesis has Alpha error states that the null hypothesis has been wrongly acceptedbeen wrongly accepted
� Power of a study can be increased by raising the number of observations
TTFFTTTFFT
BJA, CEACCPBJA, CEACCP
�� The The nullnull hypothesishypothesis would therefore be would therefore be
that intrathat intra--articular morphine is no betterarticular morphine is no better
than placebo.than placebo.
�� A type I A type I error ( alpha)error ( alpha) occurs when the occurs when the
null hypothesis is incorrectly rejected. A null hypothesis is incorrectly rejected. A
type II type II errorerror (beta) occurs when the null (beta) occurs when the null
hypothesis is incorrectly acceptedhypothesis is incorrectly accepted
GOOD LUCKGOOD LUCK