PULMONARY FUNCTION TESTS LEARNING OBJECTIVES By the

PULMONARY FUNCTION TESTS
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LEARNING OBJECTIVES
By the end of the lecture, the student should be able to know:
Categories of pulmonary function tests
Indications for PFTs
Define spirometry and types
Define and interpret spirometry indices and graphs
Elaborate obstructive and restrictive disease and PFTs
How to perform spirometry
HISTORICAL PERSPECTIVE
John Hutchison , 1811-1861 invented the Spirometer
Coined the term “VITAL CAPACITY”
Measured the vital capacity of 2,130 individuals
Found that VC was directly related to height and inversely to age.
Weight only had a minor influence
Reduction in VC were related to early death
Not widely accepted
CATEGORIES OF PULMONARY FUNCTION TESTS
REST:
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SPIROMETRY
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Measurement of Lung Volumes
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Airway Resistance
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Diffusing Capacity (DLCO)
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Arterial Blood gases (PO2, PCO2, pH)
EXERCISE
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6 Minute walk Test ( distance, heart rate and pulse oximetry)
Non-invasive Progressive Exercise Test
Invasive Progressive Exercise Test
SLEEP STUDY
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Nocturnal abnormalities of ventilation
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INDICATIONS OF PFTs
Detect the presence or absence of pulmonary disease
– History of symptoms
• Dyspnea, Wheezing
• Cough, Chest pain
– Physical signs
• Decreased breath sounds
• Chest wall abnormalities
– Abnormal Lab findings
• Chest Xray
• Arterial Blood gases
INDICATIONS OF PFT’s
Severity of known disease
Response to therapy
Occupational exposure
Assess risk of surgery
Evaluate for disability
SPIROMETRY
Spirometry is a method of assessing lung function by measuring
the volume of air the patient can expel from the lungs after a
maximal expiration.
TYPES OF SPIROMETERS
Bellows spirometers:
Measure volume; mainly in lung function units
Electronic desk top spirometers:
Measure flow and volume with real time display
Small hand-held spirometers:
Inexpensive and quick to use but no print out
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STANDARD SPIROMETRIC INDICIES
FEV1 - Forced expiratory volume in one second:
The volume of air expired in the first second of the blow
FVC - Forced vital capacity:
The total volume of air that can be forcibly exhaled in one breath
FEV1/FVC ratio:
The fraction of air exhaled in the first second relative to the total
volume exhaled
ADDITIONAL SPIROMETRIC INDICIES
VC - Vital capacity:
A volume of a full breath exhaled in the patient’s own time and not forced.
Often slightly greater than the FVC, particularly in COPD
MEFR – Mid-expiratory flow rates:
Derived from the mid portion of the flow volume curve but is not useful
for COPD diagnosis
LUNG VOLUMES
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ABSOLUTE LUNG VOLUMES
SLOW VITAL CAPACITY (SVC):
– The maximal amount of air exhaled slowly after a maximal
inspiration
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RESIDUAL VOLUME (RV):
– The amount of air left in the lung after maximal exhalation
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TOTAL LUNG CAPACITY (TLC):
– The amount of air in the lungs after a maximal inhalation
FVC MANEUVER:
“The subject inhales maximally and then exhales as rapidly and
completely as possible”
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SPIROGRAM
FLOW VOLUME CURVE
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INTERPRETING SPIROMETRY
Normal (predicted) values have been defined for large populations and
are based upon sex, age, height and race.
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Spirometric values are expressed as percent of predicted
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Generally >80% of predicted is normal, 60-79 is mildly reduced, 4059% moderately reduced and <40% severe
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TWO GENERAL PATTERNS
Obstructive: Cannot get the air out because airways collapse on
expiration, lungs are hyperinflated because gas is trapped
Restrictive disease: Can’t get the volume in because lungs are
scarred or infiltrated or muscles are weak. Characterized by decreased
lung volumes
FLOW/VOLUME LOOPS
OBSTRUCTIVE VS RESTRICTIVE VENTILATORY DEFECT
HOW TO PERFORM SPIROMETRY
WITHHOLDING MEDICATIONS
Before performing spirometry, withhold:
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Short acting β2-agonists for 6 hours
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Long acting β2-agonists for 12 hours
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Ipratropium for 6 hours
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Tiotropium for 24 hours
Optimally, subjects should avoid caffeine and cigarette smoking for 30
minutes before performing spirometry
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PERFORMING SPIROMETRY - PREPARATION
Explain the purpose of the test and demonstrate the procedure
Record the patient’s age, height and gender and enter on the
spirometer
Note when bronchodilator was last used
Have the patient sitting comfortably
Loosen any tight clothing
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PERFORMING SPIROMETRY
Breath in until the lungs are full
Hold the breath and seal the lips tightly around a clean mouthpiece
Blast the air out as forcibly and fast as possible. Provide lots of
encouragement!
Continue blowing until the lungs feel empty
Watch the patient during the blow to assure the lips are sealed around
the mouthpiece
Check to determine if an adequate trace has been achieved
Repeat the procedure at least twice more until ideally 3 readings within
100 ml or 5% of each other are obtained
BRONCHODILATOR REVERSIBILITY TESTING
Results:
An increase in FEV1 : > 200 ml and 12% above the pre-bronchodilator
FEV1 (baseline value) is considered significant
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AN APPROACH TO INTERPRETING PFT’s
Validity of the test
Reproducibility of the test
- Expiratory time
AN APPROACH TO INTERPRETING PFT’s
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STEP I
– FEV1/FVC Ratio
• If reduced to <75% then obstructive process is likely present
• If normal or increased then a restrictive process is likely
present
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STEP II
– FVC Value
• If normal any restriction is unlikely
• If reduced , either obstruction or restriction
– FEV1 Value
• If normal, significant obstruction or restriction is ruled out
• If reduced by >20% then either restrictive or obstructive
disease
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STEP III
– Expiratory flow values ( FEF25-75)
• Reduced with normal FVC & FEV1, it may suggest early
obstructive disease
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STEP IV
- Bronchodilator response
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Increased ( >12% or 200ml ) Represents hyper-responsive
airways ( Asthma, COPD)
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