Lecture 13- Pulmonary lung function tests Flashcards
PFTs are tests that measure
- Lung volumes
- Rate of airflow
- Gas exchange (alveolar-vascular membrane)
PFTs used to
- diagnose patients with resp symptoms
- establish severity and progression of lung disease
- assess treatment response
- monitor patients on meds with lung toxicity
- Instruments used
- peak flow meter
- spirometry
- diffusing capacity of CO (DLCO)- provides info about alveolar-capillary membrane diffusing capacity
define peak expiratory flow
Maximum airflow rate attained during forced expiration (PEFR)
normal peak PEFR
- Normal >80% of predicted average based on
- Ethnicity
- Height
- Gender
- Age
what is used to measure PEFR
peak flow meter
baseline PEFR measured when
when pt is asymptomatic
- PEFR Useful in monitoring people with
asthma
Spirometry
- Used to measure some lung volumes
- Calculates airflow as volumes are measured over time
- Reports those values
- Also produces graphical representations
graph which can be produced by spirometry
Which values will spirometry give
- Tidal volume
- Inspiratory reserve volume
- Expiratory reserve volume
- Inspiratory capacity
- Forced expiratory volume in 1 second (FEV1)
- Forced vital capacity (FCV)
- FEV1/FVC
- Tidal volume
- Breathing quietly
- How much air you breathe in and out of the lungs
- Inspiratory reserve volume
Extra air inspired above and beyond normal inspiration (tidal volume)
- Expiratory reserve volume
Extra air expired above and beyond normal expiration
-
Residual volume
*
- Air left in lungs after expiratory reserve volume
- Spirometry cant measure this- can only measure air that can be blown or sucked into tube
- Functional reserve volume
= expiratory reserve volume + residual volume
- Also cant measure this using spirometry
- Represents the balance between lung inner elastic recoil and chest wall outer elastic recoil
- Volume of air left when the forces are equally balanced
- Inspiratory capacity
Amount of air I can breathe in (tidal volume) + inspiratory reserve volume
- Vital capacity
Amount of air breathe out after maximum inspiration
- Total lung capacity
- Vital capacity + residual volume
- Spirometry cant give this
- Vital capacity + residual volume
- Forced expiratory volume in 1 second (FEV1)
- maximum volume of can be forcefully expired within 1 second after maximal inspiration
- Forced vital capacity (FCV)
- total amount of air exhaled after maximal inspiration during entire FEV test – occurs over 6 seconds
- FEV1/FVC r
-
epresents proportion of patients forced vital capacity that they are able to expire in first second of forced expiration
- FEV1:FVC <70% (0.7) obstructive airway disease
volume time plot
shows FEV1 and FVC graphically
- characteristic shape
-
Healthy plot
- FEV1 = 4l
- FVC= 5l
Flow volume loops (spirotmetry doesn’t measure these)
- Volume of air present in lungs at transition maximum inspiration expiration = total lung capacity
- Volume of air present in lungs transition expiration to inspiration= residual volume (RV)
example of obstructive lung disease
COPD and asthma
volume time plot and flow voluem loops in obstructive diease
Volume time plot
- Asthma/COPD – full line
- FEV1 is less than normal person
- FEV1= 1.5 in asthma/COPD / FEV1= 4 in normal peron
- therefore FEV1/FVC ratio <70%
- FCV will be pretty normal- jsut takes longer to get to maxinal value
Flow volume loop
- We are looking at the shape
- Full line = obstructive lung disease (COPD/Asthma)
- Peak flow rate less (peak flow meter can also measure this)
- Coving/notching on expiration
- Peak flow rate falls quicker
- Marked obstruction of flow during expiration
- Not much difference on expiration
- Peak flow rate less (peak flow meter can also measure this)
main feature of obstrucitve lung disease
- OBstrUtive
- O= harder to breath OUT
- B= PFTs BELOW normal value
- U= UPPER value (numerator) reduced)
Obstructive disease and FEV1
will bedecreased by more than 70%
- how much FEV1 decreased below normal provides ifno about disease severity
COPD and FVC
FVC initially normla, will decrease in severe disease
asthma and FVC
FVC typically decreased- small airways close prematurely
key diagnostic finding for obstructive lung disease
FEV1:FVC <0.7
Obstructive kung disease and TLC (total lung capcity) and FRC (functional residual capacity)
if there is air trapping because iof small airway collapse- TLC and FRC will be increased because of increased residual volume (RV)–> air lef tin the lungs after breathing out
how to determine if the obstructive lugn disease is asthma or COPD
PT given bronchodilator after baseline spirometry is taken and the values are compared
- FEV1 12% or greater after bronchodilator – asthma
- Not greater after bronchodilator in COPD
- COPD is irreversible lung disease (minimal response to Beta agonists inhalers)
- some people will have some degree of revrsibility through inhalers- most wont
examples of restrictive lung disease
ILD and myasthenia gravis (chest wall weaker in MG)
Restrictive lung disease also known as
- stiff lungs
in restictive lung disease stiff lungs means
- hard to expand- hard to inspire (breathe in)
- return to original volume very quickly (very elastic)
why are lungs stiff in restrictive lung disease
inbalance between lung elastic recoil and chest elastic recoil
volume time plot and flow volume loop for restrcitve lung disease
Volume time plot
-
FEV1 can be normal- will typically be reduced though
- Amount of air that can be removed in 1s- if you have smaller amount of air in lungs- going to be less air to blow out
- Not that they cant get it out quickly
-
FVC markedly decreased
- Less air in lungs to begin with due to stiffness of lungs reducing the amount of air in the lungs to start with
Flow volume loop
- Shape is the same as healthy lung
- Total volume being moved in/out of lungs markedly decreased
DLCO- not part of ……………….- part of PFTs
spirometry
DLCO stands for
- Diffusing capacity carbon monoxide
- Determines how much oxygen travels from alveoli of lungs to bloodstream i.e. diffusion
PFT results restrictive lung disease
- normal/increased FEV/FVC ration (both may be reduced, but FVC is most markedly reduced)
- TLC and FRC will be reduced to reduced lung capacity
DLCO can provide info on
- Can provide info about alveolar-capillary membrane
- Can be decreased in many conditions including
in which conditions may DLCO be reduced
- Emphysema – decreased SA
- Alveolar inflammation- increased thickness due to pus
- Pulmonary fibrosis – increased thickness
- These conditions would have normal spirometry or chest x-ray
So what does an abnormal DLCO with normal chest x-ray and spirometry suggest?
Suggests problem with vascular part of membrane
-
Idiopathic pulmonary arterial hypertension
- Pulmonary arterial become thickened- impaired diffusion
- Drugs that supress appetite can cause this- don’t know why
-
Chronic thrombo-embolic disease of lungs
- Need other tests to confirm
volume time plot for different disease state
flow volume loops in different disease states
How do you differentiate different restrictive lung disease
By looking at the DLCO
DLCO in myasthenia gravis (RLD)
- Restrictive pattern on spirometer
- DLCO will be normal (problem with the lung parenchyma (muscle) not the alveolar capillary barrier
- ILD and DLCO
- Restrictive pattern on spirometry
- Abnormal DLCO- thickening of barrier between alveoli and capillaries
Summaery table comparing obstructive and restrictive PFTS
