Pulmonary Function Measurements Part 1
Static Lung Volumes
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Tidal Volume: (VT) 5-7 mL/kg or 500 mL
Inspiratory Reserve Volume: (IRV) 3100 mL
Expiratory Reserve Volume: (ERV) 1200 mL
Residual Volume: (RV) 1200 mL
Capcities?
Residual Volume Measurements
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Measured indirectly by:
Closed circuit helium dilution
Open circuit nitrogen washout
Body plethysmography
Closed Circuit Helium Dilution (1)
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Inhale known volume of air (V1)
(1)
V1 contains a known fraction of helium (FHe1) at
end-expiration of tidal breathing (when the volume
left in the lungs is equal to FRC)
After equilibrium, the fraction of helium
is measured (FHe2)
FRC = V1(FHe1-FHe2) / FHe2
Indirectly measures residual volume
Open Circuit Nitrogen Washout
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Pt. inhales through a two-way valve connected
o to 100% O2
Pt. exhales into a collection spirometer
Spirometer measures each breath for
o Volume of air
o FN2
Once the FN2 < 1.5% for 3 consecutive breaths
o the test is complete.
FRC = V exhaled X C exhaled N2 / C initial alveolar N2
Air we breath has 78% Nitrogen
Body Plethysmography
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Based on Boyles Law
Closed system with constant temperature
P1V1=P2PV2
Static Lung Volumes
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Significance of changes in FRC and RV
• Increased FRC = hyperinflation
• Increased FRC + RV = obstructive pattern
• Decreased FRC + RV = restrictive pattern
RV/TLC = 20% to 35%
FRC = ERV + RV
Comparison of Static Lung Volume
Pulmonary Mechanics
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Expiratory flow rate measurements
• Integrity of airways
• Severity of airway impairment
• Large or small airway problem.
• Volume vs flow rate?
Pulmonary Mechanics Measurements
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Forced vital capacity (FVC)
Forced expiratory volume timed (FEVT)
Forced expiratory volume1sec/forced vital capacity ratio (FEV1/FVC ratio)
Forced expiratory flow25%-75% (FEF25%-75%).
Forced expiratory flow200-1200 (FEF200-1200)
Peak expiratory flow rate (PEFR)
Maximum voluntary ventilation (MVV)
Flow-volume loop.
FVC
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Maximum volume of gas that can be exhaled as forcefully
and rapidly as possible after maximal inspiration.
Forced vital capacity
Done after maximum inspiration or exhalation
Breakout Session
 Explain the way air trapping produces both of the following abnormal test results:
(1) Thoracic gas volume (TGV), as obtained by plethysmography,
is different from the TLC determined by nitrogen washout.
o Nitrogen wash out doesn’t measure… thoracic gas volume is going to be greater than
that determined by nitrogen was how is there is gas hidden between blocked airway.
(2) FVC is different from the slow VC
o FVC Maximum volume of gas that can be exhaled as forcefully and rapidly as possible
after maximal inspiration.
o VC the greatest volume of air that can be expelled from the lungs after taking the
deepest possible breath.
Forced Expiratory Volume Timed (FEVT)
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Maximum volume of gas that can be exhaled within specific time period
• Measurement obtained from FVC
• Most frequently used time period:
• 1 second = FEV1.
• FVC = 3.5 L
• FEV1 = 2.5 L
Normal FEVT
• Normal percentage of total FVC exhaled during these time
periods:
• FEV0.5 - 60% of FVC
• FEV1 - 83% of FVC.
• Normal percentage of total FVC exhaled during these time periods:
• FEV2 - 94% of FVC
• FEV3 - 97% of FVC.
FEV1/FVC Ratio
• Compares
• FEV1 to FVC
• Commonly referred to as forced expiratory volume in 1 second percentage
• FEV1/FVC < 70% = abnormal airway obstruction present
• AKA - FEV1%.
FVC, FEV1, and the FEV1/FVC
• Most common flow measurements
• Obstructive VS Restrictive
• Severity of pulmonary disorder
Obstructive VS Restrictive Lung Disorder
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Obstructive
o Decrease FEV1
o Decrease FEV1/FVC
Restrictive
o FEV1 normal or Decrease
o FVC decreased
FEF25%-75%
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Average flow rate that occurs during
middle 50% of FVC measurement
Medium to small airways pose
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the major resistance to expiratory
flow over this part of the FVC
“Mid flows”
Peak Expiratory Flow Rate (PEFR)
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Maximum flow rate that can be achieved
during FVC maneuver
Occurs in very early part of the FVC
Large airways pose the major flow resistance
in this part of the FVC
Maximum Voluntary Ventilation (MVV)
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Largest volume of gas that can be breathed voluntarily in
and out of lung in 1 minute
15seconds*4 or 12seconds*5
Dynamic Pulmonary Mechanics Measurements
Flow-Volume Loop
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Graphic presentation of FVC maneuver followed by forced inspiratory volume (FIV) maneuver
X-axis= volume (liters)
Y-axis= flow (L/second)
Measures forced inspiratory and expiratory flow rate
Augments spirometry results
Indications: evaluation of upper airway obstruction (stridor, unexplained dyspnea), evaluation
of patient to identify obstructive vs restrictive pulmonary problems
FVC and Flow-Volume Loop
Practice
Find:
1. Peak Expiratory Flow Rate
2. Forced Vital Capacity
3. FEV1
4. Peak Inspiratory Flow Rate
5. FEV1/FVC (calculate)
1. Peak Expiratory Flow Rate
2. Forced Vital Capacity
3. FEV1
4. Peak Inspiratory Flow Rate
5. FEV1/FVC (calculate)