chapter 9 pulmonary function testing
DESCRIPTION
Chapter 9 Pulmonary Function Testing. Overview. PFT includes: Spirometry Flow volume loop (FVL) before and after bronchodilator inhalation Lung volume studies Diffusing capacity (D LCO ) Airway resistance (Raw) Arterial blood gas (ABG) measurements - PowerPoint PPT PresentationTRANSCRIPT
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Chapter 9Pulmonary Function Testing
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Overview
PFT includes: 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
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
PFT normal values vary with age, height, gender, and race
Height the most important factor predicting lung volumes 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
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
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
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)
Tidal volume Volume during quiet breathing Adults: 350 to 600 ml Stiff lungs: small volumes at higher rate Obstruction: normal volume at slower rate
Minute volume Rate x volume 4 to 8 L/min
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Measures of Lung Function (cont’d)
Vital capacity: maximal volume exhaled Measured after deepest breath possible Slow vital capacity (SVC) Forced vital capacity (FVC)
Proper coaching is essential Phases
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)
Total lung capacity Sum of SVC and RV Normal % predicted is 80% to 120% Increased in obstructive diseases due to air
trapping Obtained by body plethysmography, open-
circuit nitrogen washout, closed-circuit helium dilution, XR planimetry
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Body Plethysmography
Boyle’s law 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
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
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.
If air trapping is present this technique will underestimate total intrathoracic volume
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Closed-System Helium Dilution
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
Residual volume (RV) Gas left after exhalation Obtained from TLC studies TLC-SVC or FRC-ERV Increased in air trapping
Expiratory reserve volume (ERV) Maximal gas exhaled from resting status
Functional residual capacity (FRC) 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
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
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
3-second point of the expiratory curve Not as reproducible as FEV1
Reported as % of the FVC (normal ~95%) FEF25%-75%
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
Maximum flow rate achieved during FVC maneuver
Effort dependent Peak flowmeters are inexpensive Asthma action plans
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
Patient breathes as rapidly and deeply as possible for 12 to 15 seconds
Extrapolated to obtain MMV in 1 minute MMV reflects:
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)
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
FVC, FEV1, FEF25%-75% and FVL to assess reversibility
Amount of change required to qualify as improvement FVC >10% FEV1 >200 ml or >15% FEF25%-75% >20% to 30%
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Diffusion Capacity (DL)
Determinants of gas exchange 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 Normal: 80% to 120% predicted
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Bronchoprovocation Testing
Diagnosis of occult asthma Provoking agents
Inhaled histamine or methacholine Exercise Cold air
A 20% decrease in FEV1 indicates hyperreactive airways
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Other Applications of PFT
Smoking cessation Surgery Sleep apnea Environmental lung disease
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Obstructive and Restrictive Disorders
Obstructive Expiratory flow <80% predicted TLC >80% predicted (air trapping) Obstruction changes flow volume loop (FVL) Fixed: flattened expiratory and inspiratory limbs
of FVL Restrictive
Lung volume <80% predicted
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Approach to PFT Interpretation
If FVC >80% predicted = no restrictive <80% predicted = look at TLC
If TLC >80% predicted = no restrictive <80% predicted = restrictive
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Approach to PFT Interpretation (cont’d)
FEV1 and FEF25%-75%
FEV1 normal and FEF25%-75% <65% predicted = mild obstructive disease
Response to bronchodilator If FVC, FEV1, FEF25%-75% improve = response
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Approach to PFT Interpretation (cont’d)
FVL 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
Asthma Low FEV1 and FEF25%-75%; normal TLC; normal
DL; response to bronchodilator Emphysema
Low FEV1 and FEF25%-75%; normal TLC; low DL; no response to bronchodilator
Pulmonary fibrosis Low FVC; low FEV1 but normal FEV1/FVC;
small TLC, low DL; no response to bronchodilator