Chapter 9
Pulmonary Function Testing
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Overview
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PFT includes:
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Spirometry
Flow volume loop (FVL) before and after
bronchodilator inhalation
Lung volume studies
Diffusing capacity (DLCO)
Airway resistance (Raw)
Arterial blood gas (ABG) measurements
Pulmonary response to exercise and bronchial
provocation
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Purpose of PFT
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Evaluate cause of pulmonary symptoms
Evaluate abnormalities seen on the CXR
and/or CT scan
Follow course of disease and response to
treatment
Evaluate perioperative risk for pulmonary
complications
Rule out pulmonary pathology in people
with high risk for pulmonary dysfunction
Evaluate disability
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Normal Values
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PFT normal values vary with age, height,
gender, and race
Height the most important factor predicting
lung volumes
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The taller the person, the larger the values
Weight important when BMI >30 =
restrictive
Gender: males have larger lungs
Race: African Americans, Asians, East
Indians have 12% smaller lung volumes
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PFT Equipment
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American Thoracic Society standards
Spirometer: routine flows and volume
Body plethysmograph: TLC and airway
resistance studies
Diffusion system: lung diffusion
Gas analysis (carbon dioxide, carbon
monoxide, helium, nitrogen, and oxygen)
Nebulizer equipment for albuterol and
methacholine
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Arterial blood gas analyzer
Treadmill or bicycle for exercise evaluation
Laboratories with smaller volumes of tests
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Multifunction device that measures lung
volumes, flow rates, diffusing capacity, and
response to bronchial provocation
all spirometric values obtained under
ambient conditions convert to
Body temperature, ambient pressure,
saturated (BTPS)
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Measures of Lung Function
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Tidal volume (VT)
Residual volume (RV)
Expiratory reserve volume (ERV)
Inspiratory reserve volume (IRV)
Minute volume (VE)
Vital capacity (VC)
Total lung capacity (TLC)
Functional residual capacity (FRC)
Inspiratory capacity (IC)
Maximal voluntary ventilation (MVV)
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Measures of Lung Function
(cont’d)
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Tidal volume
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Volume during quiet breathing
Adults: 350 to 600 ml
Stiff lungs: small volumes at higher rate
Obstruction: normal volume at slower rate
Minute volume
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Rate x volume
4 to 8 L/min
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Measures of Lung Function
(cont’d)
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Vital capacity: maximal volume exhaled
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Proper coaching is essential
Phases
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Measured after deepest breath possible
Slow vital capacity (SVC)
Forced vital capacity (FVC)
Maximal inspiratory effort
Initial expiratory blast
Forceful emptying of lungs
<20 ml/kg: risk for complications
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Measures of Lung Function
(cont’d)
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Total lung capacity
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Sum of SVC and RV
Normal % predicted is 80% to 120%
Increased in obstructive diseases due to air
trapping
Obtained by body plethysmography, opencircuit nitrogen washout, closed-circuit helium
dilution, XR planimetry
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Body Plethysmography
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Boyle’s law
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Pressure and volume of a gas vary inversely if
temperature is constant
Accurate but body box is expensive
A Calibrated 3l sirynge is use to
determine the accuracy of a water-sealed
spirometer in measuring lung volumes
Used to measure Lung Volumes
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Nitrogen Washout
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To determine distribution of ventilation
Patient breathes 100% oxygen
Nitrogen analyzer measures diminishing
N2 concentration from lungs
Well-ventilated units empty first
Uneven pattern common in obstructive
lung disease
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Nitrogen Washout
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Oxygen 100% for 7 minutes or until
nitrogen is washed out of patient’s lungs,
by putting an amount of know oxygen
volume we can estimate lung volume, 79%
of RV is NITROGEN.
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If air trapping is present this technique will
underestimate total intrathoracic volume
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Closed-System Helium Dilution
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Helium is inhaled and not significantly
absorbed from lungs by blood
Helium is diluted in proportion to size of
lung volume being measured
Equilibrium takes 7 minutes
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RV, ERV, and FRC
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Residual volume (RV)
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Expiratory reserve volume (ERV)
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Gas left after exhalation
Obtained from TLC studies
TLC-SVC or FRC-ERV
Increased in air trapping
Maximal gas exhaled from resting status
Functional residual capacity (FRC)
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Gas left after full exhalation at resting status
3 way of measuring FRC are Helium, body
box, and Nitrogen Washout
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Indices of Flows
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Forced expiratory volume at 1 sec (FEV1)
Forced expiratory volume at 3 sec (FEV3)
Forced expiratory flow, mid-expiratory
(FEF25%-75%)
Peak expiratory flow (PEF)
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FEV1
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Maximal volume exhaled during 1st
second of expiration
It is a forced maneuver
Varies with age, gender, race, and height
The % predicted is 80% to 100%
Reduced in obstructive and restrictive lung
disease
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FEV3
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3-second point of the expiratory curve
Not as reproducible as FEV1
Reported as % of the FVC (normal ~95%)
FEF25%-75%
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Average flow rate during middle half of
expiratory curve
Normal 65% to 100%
More sensitive to airway obstruction than FEV1
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Peak Expiratory Flow
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Maximum flow rate achieved during FVC
maneuver
Effort dependent
Peak flowmeters are inexpensive
Asthma action plans
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Green zone: 80% to 100% of personal best
Yellow zone: 50% to 80%
Red zone: <50% = urgent physician
intervention
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Maximal Voluntary Ventilation
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Patient breathes as rapidly and deeply as
possible for 12 to 15 seconds
Extrapolated to obtain MMV in 1 minute
MMV reflects:
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Status of respiratory muscles
Compliance of thorax-lung complex
Airway resistance
Patient motivation and ability to move air
Important in the preoperative patient
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Flow Volume Curves (Loops)
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Volume plotted on horizontal axis and flow
on vertical axis
Fixed or variable upper airway obstruction
COPD/asthma
Restrictive lung disease
Pre- and postbronchodilator curves
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PFT Before and After
Bronchodilators
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FVC, FEV1, FEF25%-75% and FVL to assess
reversibility
Amount of change required to qualify as
improvement
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FVC >10%
FEV1 >200 ml or >15%
FEF25%-75% >20% to 30%
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Diffusion Capacity (DL)
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Determinants of gas exchange
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Surface area of membrane
Thickness of membrane
Hemoglobin and blood flow in capillaries
Measures crossing of co from Alveoli to cap
and back
Pt breaths in mixture of 4% CO and 16%
Helium. Holds breath for 10-12 sec.
Machine reads time of CO crossing
membrane and back.
DLCO-SB
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Normal: 80% to 120% predicted
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Bronchoprovocation Testing
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Diagnosis of occult asthma
Provoking agents
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Inhaled histamine or methacholine
Exercise
Cold air
A 20% decrease in FEV1 indicates
hyperreactive airways
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Other Applications of PFT
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Smoking cessation
Surgery
Sleep apnea
Environmental lung disease
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Obstructive and Restrictive
Disorders
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Obstructive
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Expiratory flow <80% predicted
TLC >80% predicted (air trapping)
Obstruction changes flow volume loop (FVL)
Fixed: flattened expiratory and inspiratory
limbs of FVL
Restrictive
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Lung volume <80% predicted
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Approach to PFT Interpretation
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If FVC
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>80% predicted = no restrictive
<80% predicted = look at TLC
If TLC
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>80% predicted = no restrictive
<80% predicted = restrictive
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Approach to PFT Interpretation
(cont’d)
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FEV1 and FEF25%-75%
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FEV1 normal and FEF25%-75% <65% predicted =
mild obstructive disease
Response to bronchodilator
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If FVC, FEV1, FEF25%-75% improve = response
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Approach to PFT Interpretation
(cont’d)
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FVL
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Scooping of expiratory limb = obstructive
Flattening inspiratory and expiratory limbs =
fixed or variable large airway obstruction
DL >80% predicted is normal
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Pattern Recognition
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Asthma
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Emphysema
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Low FEV1 and FEF25%-75%; normal TLC; normal
DL; response to bronchodilator
Low FEV1 and FEF25%-75%; normal TLC; low DL;
no response to bronchodilator
Pulmonary fibrosis
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Low FVC; low FEV1 but normal FEV1/FVC;
small TLC, low DL; no response to
bronchodilator
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