PFTs Flashcards
pulmonary function tests
-Categorize the nature and severity of disease
-Follow the progression of disease
-Measure response to therapy
-Define disability
-Pre-op evaluation
-Screening at risk populations
-Monitoring drug toxicity (chemo)
what do lung volumes measure
-IRV- inspiratory reserve volume
-Vt- tidal volume - normal breathing
-TLC- total lung capacity
-RV- residual volume - always there
-ERV- expiratory reserve volume - force exhalation
-IC- inspiratory capacity- forced inhalation + tidal
know the chart of diff lung volumes
-
spirometry
-measures rates at which lung changes volumes during forced breathing maneuvers
-begins with full inhalation and is followed by forced exhalation that rapidly empties lung
-exhalation is continued for as long as possible or until plateau is reached
2 ways to graph spirometry maneuvers
-1. volume time curve
-2. flow volume loop (dont need to know as well)
spirometry: volume time curve
-simple office based
-measures flow, volumes
-volume vs time
-can determine:
-forced expiratory volume in 1 second (FEV1)
-forced vital capacity (FVC)
-FEV1/FVC
FVC
-forced vital capacity
-majority of air comes out in first 1s (<3s)
-total volume of air that can be exhaled forcefully from TLC
-FVC is prolonged in obstructive disease
-measured in liters (L)
-normal 80
FVC ranges
> 80% Normal
70-79% Mild reduction
50%-69% Moderate reduction
<50% Severe reduction
FEV1
-Forced expiratory volume in 1 second: (FEV1)
-Volume of air forcefully expired from full inflation (TLC) in the first second
-Measured in liters (L)
-measures severity of COPD*
-Normal people can exhale more than 75-80% of their FVC in 1st second -> FEV1/FVC can be utilized to characterize lung disease
FEV1 ranges
> 80% Normal
70%-79% Mild obstruction
50-69% Moderate obstruction
<50% Severe obstruction
FEV1/FVC range
-normal - 90%
-COPD - 60%
-restrictive- normal ratio (but low FEV1 and FVC)
guiding principles to interpreting pulmonary function tests
-1. examine curves
-2. examine FEV1/FVC ratio
-3. examine FEV1 value
-normal curve plateaus at 3s
-obstructive- prolonged plateau (even up to 10s)
-restrictive- shorter (less volume in and out)
normal values are based on
-race
-height
-age
-sex
interpreting spirometry results: guidelines
-FVC, FEV1, and FEV1/FVC ratio are used
-confident dx with high or low values
-low FEV1/FVC ratio is hallmark of airflow obstruction
-classify severity using FEV1 expressed as % of predicted value
-determine response to bronchodilator therapy to eval reversibility
-spirometry also measures restrictive
-restrictive lung disease requires additional studies**
flow volume loops
-shows max expiratory and inspiratory flow volumes curves
-useful to help characterize disease states (obstructive vs restrictive)
-normal- right triangle
-obstructive- depressed curve
-dont need to interpret for test
-restrictive- narrower triangle
obstructive disease
-decreased FEV1
-decreased FVC
-decreased FEV1/FVC -> >90% of predicated value is considered normal
-FEV1 much lower than FVC
-FEV1 used to follow severity in COPD
bronchodilator response
-degree to which FEV1 improves with inhaled bronchodilator
-documents reversible airflow obstruction
-significant response if: FEV1 increases by 12% AND <200 -> fully reversible**
-request if obstructive pattern on spirometry
-reversible - asthma (rather than COPD)
-you dont give beta agonist for restrictive
bronchoprovocation
-Useful for diagnosis of asthma in the setting of normal pulmonary function tests
-brings on an attack in controlled setting
-Common agents: Methacholine, Histamine, others
-Diagnostic if: ≥20% decrease in FEV1
emphysema
-floppy airways -> TOO compliant
-bulla
-destruction of alveoli
-low recoil pressure
diffusing capacity
-alveoli issue
-issue with blood flow to alveoli
-basement membrane between alveoli and capillaries
-DETERMINED BY:
-SA of alveoli
-thickness of alveolar membrane
-volume of blood in capillary bed
-reaction rate of test gas (CO) with Hgb
decrease DLCO (diffusing capacity of the lungs for carbon monoxide)
-<80% predicted)
-obstructive lung disease (emphysema)
-parenchymal disease (alveolar disease)
-pulmonary vascular disease (PE, PHTN)
-anemia
increased DLCO (diffusing capacity of the lungs for carbon monoxide)
->120%-140% predicted
-pulmonary hemorrhage
-polycythemia
-left to right shunt
residual volume WNL
80-120
restrictive pattern
-decrease FEV1
-decrease FVC
-FEV1/FVC normal or increased
-flow volume curve is steeper- 3L
-high recoil pressure and low compliance
spirometry CANNOT measure
-TLC
-FRC
-RV
TLC and RV in obstructive and restrictive lungs
-obstrucitve: HIGH
-TLC > 120% predicted
-RV > 120% predicted
-restrictive: LOW
-TLC < 80% predicted
-RV < 80% predicted
