20/04/16
CRFS Workshop
ANZSRS 2016 ASM
The
NUTS & BOLTS
of
Spirometry
Mahesh Dharmakumara
Respiratory Scientist
The Alfred Hospital
Melbourne, VIC.
DISCLOSURE
The presenter has advised that the following presentation will NOT include
discussion on any specific commercial products or service and that there are
NO financial interests or relationships with any of the Commercial Supporters
of this years ASM.
REFERENCES
• Alfred Hospital Lung Function Laboratory, Principles and Practice of
Spirometry, 2-Day Course, 2016.
• ATS/ERS Task Force. Standardisation of Spirometry, 2005.
• Borg, B. et al. Interpreting Lung Function Tests: A Step-by-Step Guide.
Wiley-Blackwell Publishing, 2014.
• Ruppel G. Manual of Pulmonary Function Testing (8th ed), St Louis: Mosby
Year Book, 2003.
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CRFS Workshop
Practice Question
Q.
Why have you decided to attend this workshop?
A. To understand fundamental concepts
B. To refresh my knowledge
C. To work through some practice questions
D. All of the above
OUTLINE
• BTPS
• Calibration
• Spirogram
• Sensors
BTPS
LUNG
SPIROMETER
2.0 litres
1.8 litres
BTPS
ATPS
0
2.0
37o Celsius
PH2O = 47 mm Hg
0
1.8
20o Celsius
PH2O = 18 mm Hg
When we blow into a “cold” spirometer, the volume recorded by the
spirometer is less than that blown out of the lungs. Due to:
1. Gas shrinkage (Charles’ Law)
2. Condensation of water vapour (vapour pressure falls)
Alfred 2-Day Spirometry Course, 2016
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BTPS
ATPS to BTPS Conversion Factors, given on page 1 of the CRFS Exam
CALIBRATION
Description
• Calibration is the procedure in which a signal from a device is adjusted to
produce a known output.
• The adjustment assumes a profile for the relationship between an actual
value (known) and a measured value (unknown).
• This calibration profile (or curve) depends on the characteristics of the
components used in the measurement and allows derivation of a
calibration factor.
• Calibration factor is stored and applied to all subsequent measurements.
CALIBRATION
Profile
Actual Flow = Actual Volume (fixed, 3L syringe)
Measured Time (varied)
Calibration Factor =
Actual
Measured
Measured Flow = Measured Volume (signal)
Measured Time (varied)
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CALIBRATION
Derivation
Volume
Actual
(3L Syringe)
X Calibration
Factor
Measured
(Device)
Flow
Slow
Medium
Fast
Syringe Plunger Injection
Measured Value x Calibration Factor = Actual Value
CALIBRATION
Procedure
Example:
Device:
Flow Sensing
Spirometer
CALIBRATION
•
Standard:
Certified 3.0 litre
Calibration Syringe
Procedure
Volume (L) Vs. Time (sec)
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CALIBRATION
•
Volume (L) Vs. Time (sec)
CALIBRATION
•
Procedure
Flow (L/sec) Vs. Volume (L)
CALIBRATION
•
Procedure
Procedure
Flow (L/sec) Vs. Volume (L)
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CALIBRATION
Errors
• Insufficient system warm-up time
• Syringe not fully conditioned to testing environment
• Insecure connection between syringe and sensor
• Not entering ambient conditions when required
• Failure to correct any signal drift by ‘zeroing’
• Not withdrawing and injecting the syringe plunger fully
CALIBRATION
Vs. Validation
• Calibration procedure adjusts the signal whereas the validation procedure
only checks the signal.
• Validation is also known as a calibration check/test. Software may have a
‘syringe mode’ where BTPS conversion factors can be disabled for syringe
validation purposes.
•
Some types of devices or sensors do not require/allow calibration. In this
case, the way of checking if the device is within calibration limits is by
performing a validation.
• ATS/ERS 2005 states that volumes should meet the accuracy requirements
within ±3.5% of true value
CALIBRATION
Practice Question
Q. When calibrating a spirometer with a 3L syringe, the actual value divided
by the measured value is known as the:
A.
Response factor
No. This is a term used to describe a ratio in chromatography and
spectroscopy.
B.
Calibration factor
Yes. The measured value multiplied by the calibration factor equals
the actual value.
C.
Correction factor
No. While it is a type of correction factor, it is specifically not known
as this.
D.
Profile factor
No. The relationship between the actual values and a measured
values generates a calibration profile.
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CALIBRATION
Practice Question
Q55. A spirometer is tested by injecting 3 L volumes from a calibration
syringe; the results are as follows:
Trial
1
2
3
4
2.897
2.785
3.110
2.960
Which measurements DO NOT meet ATS/ERS (2005) recommendations?
A. 1 and 2
B - 1, 2 and 3
C - 2 and 3
•
•
•
•
•
•
D - 2 only
Syringe validation procedure, ±3.5% error limits
3.5% of 3.00L
3.5/100 x 3.00 = 0.105L
Upper error limit (+3%) = 3.00 + 0.105 L = 3.105L
Lower error limit (-3%) = 3.00 – 0.105 L = 2.895L
Acceptable range = Lower limit to upper limit
= 2.895L to 3.105L
•
So any value that falls outside the calculated range does not meet ARS/ERS
recommendations.
•
This includes Trials 2 and 3, therefore the answer is C.
2014 Practice Exam Paper
SPIROGRAM
Types
Two types of measured traces,
each useful for identifying different sources of error during maneuver
Complex Spirogram:
Flow (L/sec) Vs. Volume (L)
Flow (L/sec)
Volume (L)
Simple Spirogram:
Volume (L) Vs. Time (sec)
Volume (L)
Time (sec)
Alfred 2-Day Spirometry Course, 2016
SPIROGRAM
Flow
Flow
Flow
Sources of Error
Volume
Volume
Acceptable
effort
Not completely full
prior to blow
Volume
Premature termination
or glottic closure
Actual FVC
0
Time
Volume
Volume
Volume
Actual FVC
0
Time
0
Time
Alfred 2-Day Spirometry Course, 2016
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SPIROGRAM
Flow
Flow
Flow
Sources of Error
Volume
Volume
Variable or
submaximal effort
Volume
Cough or tongue
occlusion
0
Volume
Volume
Volume
Poor start
or hesitation
0
Time
Time
0
1
Time
Alfred 2-Day Spirometry Course, 2016
SPIROGRAM
Inspiration
FEF
Volume Vs. Time
Volume (L)
25-75%
FEF25%-75%
Volume (L)
FVC
FEV1
FVC
FEV1
Expiration
0
1
0
Time (sec)
1
Time (sec)
Alfred 2-Day Spirometry Course, 2016
SPIROGRAM
Volume Vs. Time
Volume (L)
• FVC: Forced Vital Capacity
FEF25%-75%
FVC
• FEV1: Forced Expired Volume in
the 1st second
FEV1
• FER: Forced Expiratory Ratio
• FEF25%-75%: Forced Expiratory Flow
between 25% and 75% of the FVC
0
1
Time (sec)
Alfred 2-Day Spirometry Course, 2016
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Volume Vs. Time:
Vitalograph Example
SPIROGRAM
Volume (L)
Vitalograph Chart Paper
• Vertical axis (left):
- Volume (L, ATPS)
- 1 small square
= 1 increment
= 0.05L or 50mL
• Horizontal axis (bottom):
- Time (sec)
- 1 small square
= 1 increment
= 0.1sec or 100msec
Time (sec)
SPIROGRAM
Volume Vs. Time
FVC:
1) Identify plateau on the curve:
• No change in volume (<0.025L) for
≥1sec, and
• Exhalation for ≥6sec in subjects
aged >10yrs and
• ≥3sec in children aged <10yrs
2) Record the corresponding value
from the Volume axis where the
plateau occurs
Volume (L)
FVC
0
SPIROGRAM
Volume Vs. Time
Volume (L)
FVC:
4L + 5 increments
= 4L + (5 x 0.05L)
= 4L + 0.25L
= 4.25L (ATPS)
Time (sec)
FVC = 4.25L
Time (sec)
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SPIROGRAM
Volume Vs. Time
FEV1:
1) Identify where the 1 second from
the start of expiration has occurred
on the Time axis
2) Record the corresponding value
from the Volume axis
Volume (L)
FEV1
0
1
SPIROGRAM
FEV1:
3.5L – (1 increment)
= 3.5L - (1 x 0.05L)
= 3.5L - 0.05L
= 3.45L (ATPS)
Time (sec)
Volume Vs. Time
Volume (L)
FEV1 = 3.45L
Time (sec)
SPIROGRAM
Volume Vs. Time
FER:
1) Determine highest acceptable
FEV1 and FVC from the trace
Volume (L)
FVC
2) Express the ratio of this FEV1
and FVC as a percentage as
follows
FEV1
FER = FEV1 x 100
FVC
0
1
Time (sec)
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SPIROGRAM
Volume Vs. Time
Volume (L)
FER:
• Highest acceptable FEV1 = 3.45L
• Highest acceptable FVC = 4.25L
= FEV1
FVC
= 3.45L
4.25L
FVC = 4.25L
FEV1 = 3.45L
= 0.81 x 100%
= 81%
Time (sec)
SPIROGRAM
Volume Vs. Time
FEF25%-75%:
1) Calculate 25% and 75% of the FVC
as follows:
25% FVC = 0.25 x FVC
75% FVC = 0.75 x FVC
Volume (L)
FEF25%-75% = Gradient
FVC
75% FVC
2) Mark these values on the curve
3) Draw a straight line through both
these points
25% FVC
0
Time (sec)
SPIROGRAM
Volume Vs. Time
FEF25%-75%:
4) Flow is calculated as the change in
volume over time which is the
gradient of this drawn line
Volume (L)
FEF25%-75% = Gradient
i.e. Flow = ∆V = Rise = Gradient
∆T Run
5) Gradient can be calculated by first
using volume value (V2) from line
for when time is 1sec
6) Then, use volume value (V1) from
intersection of the line, that is,
when time is 0sec
7) Finally,
V2
V1
0
1
Time (sec)
Gradient = V2 – V1 (L) = FEF25%-75% (L/sec)
1 (sec)
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SPIROGRAM
Volume Vs. Time
Volume (L)
FEF25%-75%:
• FVC = 4.25L
• 25% FVC
= 0.25 x 4.25L = 1.06L
FVC = 4.25L
V2 = 4.0L
• 75% FVC
= 0.75 x 4.25L = 3.19L
• Gradient
= V2 – V1 (L)
1 (sec)
= 4.0L – 0.7L = 3.30 L/sec
1sec
75% FVC
V1 = 0.7L
25% FVC
Time (sec)
SPIROGRAM
Final Reported Values:
Volume Vs. Time
Volume (L)
• Need to correct all volumes from
ATPS->BTPS.
• How? Use conversion factor from
look up table provided.
• i.e. if room temperature is 21deg
C, then factor is 1.096.
FVC
= 4.25L (ATPS) x 1.096
= 4.66L (BTPS)
Time (sec)
SPIROGRAM
• FVC: Forced Vital Capacity
Flow Vs. Volume
Expiration
‘effort dependent’
PEF
‘effort independent’
• PEF: Peak Expiratory Flow
FEF25%
• PIF: Peak Inspiratory Flow
• FEF75%: Forced Expiratory Flow at
75% of the FVC
• Shape Analysis: Determination of
acceptable effort and abnormal
concavity
Flow (L/sec)
• FEF25%: Forced Expiratory Flow at
25% of the FVC
1 sec
FEF75%
FVC
0
Volume (L)
PIF
Inspiration
Alfred 2-Day Spirometry Course, 2016
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SPIROGRAM
Flow Vs. Volume
Shape Analysis:
Normal
33yr
Obstruction
with
reversibility
Normal
60yr
Restriction
Obstruction
Obstruction
with reduced
FVC
Borg, B. et al. Interpreting Lung Function Tests: A Step-by-Step Guide. Wiley-Blackwell Publishing, 2014.
SPIROGRAM
Back Extrapolation Error
Volume
Flow
Good Start
Poor Start
0
Time
Volume
due to unsatisfactory start of expiration, characterised by
slow start or poor take off or excessive hesitation
Alfred 2-Day Spirometry Course, 2016
SPIROGRAM
•
•
•
Back Extrapolation Error
The start of the trace is determined by the back extrapolation method.
This will achieve an accurate ‘time zero’ and assure the FEV1 comes from
an acceptable curve.
Steps:
1) Ensure acceptable FVC achieved
2) Find steepest slope on the curve where PEF occurs from V-T graph
3) Draw back extrapolation line
4) Find new ‘time zero’
5) Determine extrapolated volume
6) If extrapolated volume is <5% of acceptable FVC or 0.15L (150mL),
whichever is greater, trace is acceptable
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SPIROGRAM
Back Extrapolation Error
Volume (L)
Time (sec)
ATS/ERS 2005 states that extrapolated volume must be
<5% of acceptable FVC or 0.15L (150mL), whichever is greater
Alfred 2-Day Spirometry Course, 2016
SPIROGRAM
Practice Question
Q97. From the spirogram below performed at a room temperature of 21 degC,
the FEV1 is:
A. FEV1 = 3.60 L
B. FEV1 = 3.65 L
C. FEV1 = 4.00 L
D. FEV1 = 4.60 L
Volume Increments:
0.20L or 200mL
FEV1 = 1.00L
Time Increments:
0.20sec or 200msec
2014 Practice Exam Paper.
SPIROGRAM
Practice Question
Q97. From the spirogram below performed at a room temperature of 21 degC,
the FEV1 is:
A. FEV1 = 3.60 L
FEV1 = 4.60L
B. FEV1 = 3.65 L
FEV1
= 4.60L – 1.00L
= 3.60L
C. FEV1 = 4.00 L
D. FEV1 = 4.60 L
1sec
2014 Practice Exam Paper.
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SPIROGRAM
Practice Question
Q97. From the spirogram below performed at a room temperature of 21 degC,
the FEV1 is:
A. FEV1 = 3.60 L
4.65L
B. FEV1 = 3.65 L
FEV1
= 4.65L – 1.00L
= 3.65L
C. FEV1 = 4.00 L
D. FEV1 = 4.60 L
Determine start of test using
back extrapolation method
1sec
2014 Practice Exam Paper.
SPIROGRAM
Practice Question
Bonus Question: Based on the given information, does the extrapolated
volume meet ATS/ERS recommendations?
•
Extrapolated Volume = half an increment = 100mL
•
FVC = 3.83L
•
5% of FVC = 0.05 x 3.85
= 0.193 L
= 193 mL
Is Extrapolated Volume < 5% FVC or 150mL (whichever is greater)?
100mL
< 193mL or 150mL
Yes, acceptable amount of extrapolated volume.
Therefore, calculation of FEV1 is acceptable.
SPIROGRAM
Practice Question
Q68. When an FVC manoeuvre is being performed, the respiratory
physiologist should emphasise the importance of a smooth continuous
exhalation and which of the following:
1 - Maximal effort
Yes. It is a forced manoeuvre therefore maximal
effort is required to achieve acceptable (and
repeatable) results.
2 - Unhesitating start
Yes. This is part of the start-of-test criteria to
prevent excessive extrapolated volumes.
A. 1 and 2
B. 1 and 3
3 - Avoid leaning forward
Yes. To prevent poor posture which may limit
maximal performance but also to prevent subject
from falling of chair should syncope occur.
C. 2 and 3
D. 1, 2 and 3
2014 Practice Exam Paper
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SPIROGRAM
Practice Question
Q36. The shape of the 'effort-dependent' portion of the expiratory flow
volume curve is determined by which of the following?
2 - lung elastic recoil
Yes. How quickly the lung ‘springs’ back
effects the maximum flow.
PEF
Flow (L/sec)
1 - abdominal pressure during forced expiration
Yes. The diaphragm being the main ‘pump’ drives
abdominal region to generate maximum flow.
FEF25%
1 sec
FEF75%
FVC
0
3 - flow resistance of the small airways
No. This effects small airway measures such as
FEF25%-75% which is on the ‘effort-independent’
portion of the curve.
4 - cross-sectional area of the small airways
No. This effects the resistance of the small airways
to flow, similar to 3.
Volume (L)
‘effort dependent’
‘effort independent’
A. 1 and 2 only
B. 2 and 3 only
C. 1, 3 and 4
D. 4 only
2014 Practice Exam Paper
SENSORS
Types
Two types of measuring principles:
• Volume-Displacement
Direct measure of respired volume from the displacement of a
component
• Flow-Sensing
Various physical principles used to produce a signal proportional to gas
flow
SENSORS
Volume-Displacement
-----------------------------
Wedge-Type
(Bellows)
-------------------------------
Water-Sealed
(Bell)
Dry Rolling-Seal
(Piston)
Alfred 2-Day Spirometry Course, 2016
16
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SENSORS
Turbine
(Rotation)
Fleisch
(Pneumotachograph)
Flow-Sensing
Ultrasonic
(Pulses)
Heated/Hot-Wire
(Heat-Loss)
Pitot Tube
(Pressure)
Lily / Screen
(Pneumotachograph)
Alfred 2-Day Spirometry Course, 2016
SENSORS
Volume-Displacement
Water-Sealed:
• Commonly found chain-compensated and Stead-Wells units
• Consists of a bell that is sealed from the atmosphere by water
• The bell falls and rises as the subject breathes in and out
• A pulley system is attached to the bell and the marking pens record the
subjects efforts on the rotating kymograph paper
Alfred 2-Day Spirometry Course, 2016
SENSORS
Volume-Displacement
Wedge-Type (Bellows):
• Vitalograph is the most common
• Good graphical display of Spirogram (Volume Vs. Time)
• Plastic bellows may have linearity problems
• Back pressure may be a problem
• Frequency response may be a problem
• No flow-volume loop
Alfred 2-Day Spirometry Course, 2016
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SENSORS
Volume-Displacement
Dry-Rolling Seal:
• Uses flexible silicone rubber or Teflon-coated rubber seal instead of water
• Large-volume piston moves in and out as the patient breathes
• Directly recorded by pen on paper
• Rather large units
Alfred 2-Day Spirometry Course, 2016
SENSORS
Flow-Sensing
Fleisch & Lily/Screen Pneumotachographs:
• Have a resistive element (tubes or mesh screen) in the flow tube
• Flow through pneumotach proportional to pressure difference
• Tubing connect to differential-pressure transducer
• Pneumotach must be linear over desired flow range
• Measurements vary with gas viscosity, humidity and temperature
• Good frequency response
• Usually heated to prevent condensation of expired water vapour
Alfred 2-Day Spirometry Course, 2016
SENSORS
Flow-Sensing
Turbine:
• Flow signal obtained from rotation of the turbine, counted photoelectrically
• Deposits of water droplets and dirt can change the mass of the turbine and
rotational ability and thus affect the calibration
• Fine hair/fluff can alter calibration
• Not ideal for measuring PEF
Alfred 2-Day Spirometry Course, 2016
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SENSORS
Flow-Sensing
Heated/Hot-Wire:
• Also known as heat-transfer or thermistor type
• Type of mass airflow sensors
• Heated thermistor that is cooled as gas flows past it
• Temperature transducer automatically increases and measures the flow of
electricity to the thermistor to keep it at the required temperature
• Fragile
Alfred 2-Day Spirometry Course, 2016
SENSORS
Flow-Sensing
Pitot Tube:
• It is composed of a tube inserted horizontally along the axis of the gas flow
line.
• The pressure at the end of the tube is compared with the static pressure to
determine the final gas flow rate within the flow line.
Alfred 2-Day Spirometry Course, 2016
SENSORS
Flow-Sensing
Ultrasonic:
• A pulse that travels with gas flow is sped up and against gas flow is slowed
down
• Gas flow measured from the transit times
• No moving parts
• Measurement independent of gas composition, pressure, temperature and
humidity
• Calibration not required, but validation possible
Alfred 2-Day Spirometry Course, 2016
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SENSORS
Practice Question
Q46. During repeated FVC manoeuvres using an unheated Fleisch pneumotach
the recorded dynamic volumes are observed to progressively increase. The
most likely explanation for this observation is:
A - Condensation on the resistive elements of the pneumotach is increasing
its resistance and therefore overestimating the measured flow
Yes. Flow derivation is based on resistance. Increasing resistance on sensor is
measured as increasing flow.
B - Calibration error.
No. If this was the case there would be consistent but inaccurate volumes
recorded, not progressively increasing volumes.
C - The pressure transducers are drifting.
No. If this was the case, recorded volumes may be overestimated by no
progressive increase.
D - There is excessive noise in the flow signal.
No. Recorded volumes may be inaccurate but a progressive increase would
not be seen.
2014 Practice Exam Paper
SENSORS
Practice Question
Q92. In order to measure flow using a pneumotachograph system which of the
following electromechanical devices must also be used?
A - pressure gauge
No. This is a device for only measuring the pressure of a gas.
B - spirometer
No. This is a system as a whole which includes sensor and computing
hardware.
C - differential pressure transducer
Yes. This device measures the mechanical pressure signal and converts it
into an electrical signal.
D – rotameter
No. This is a type of flow meter.
2006 & 2009 Practice Exam Paper
SENSORS
Q57. Which of the following devices has the highest frequency response?
Hint: Think about which sensor is good at measuring PEF accurately.
A - Wedge spirometer
B - Turbine peak flow meter
C - Water-seal spirometer
D - Differential pressure pneumotachograph
2006, 2009, 2014 Practice Exam Paper
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CRFS Workshop
ANZSRS 2016 ASM
A final piece of advice…
Think about
why the correct answer is right,
and
why the incorrect answer is wrong.
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