Pulm Fxn test Flashcards
When would you use a PFT?
1) Whether pulmonary disease is present 2) Type or pattern of disease present 3) Severity of disease 4) Change in disease severity over time or with therapy 5) Pre-operative clearance
`variables measured by PFTs?
1) Lung volumes
2) Airflow
3) Gas exchange
4) Compliance of the lung
5) espiratory muscle strength •
6) Airway responsivene
what are obstructive diseases
trouble getting air out
• Asthma • COPD (emphysema, chronic bronchitis) • Bronchiolitis
what are restrictive diseases
decr compliance/ability to inflate lungs
poor inspiratory muscles
• Pulmonary edema • Interstitial lung disease • Neuromuscular weakness • Pleural disease • Obesity
whatt are mixed diseases
mixed obstructive + restrictive
mechanism of spirometer
1)
spirogram looks like?
a
Difference between volumes and capacities
volumes = measured or at least estimated
single entity
everything but residual volume
capacities = sums of at least 2 volumes
define tidal volume (TV or VT)
1) volume of normal, even respiratoions at rest
2) inspiration requires effort, expiration passive
define ERV (expiratory reserve volume)
volume of gas left in lung after normal, tidal expiration that can be exhaled
requires effort
describe inspiratory reserve volume
volume of gas inhaled above that inhaled with normal tidal inspiration
requires effort
describe residual volume
if abnormal, means…
estimate or measured?
volume of gas remaining in lung at end of max expiration
if abnormal, can’t completely collapse lung
estimated (can’t measure)
define functional residual capacity
due to?
what is special about FRC?
volume of gas left in lung at end of tidal expiration
= sum of ERV + RV
volume at which elastic recoil of lung balanced by chest wall wanting to spring out
(system in equilibrium)
NO EFFORT REQUIRED
define inspiratory capacity
volume of gas maximally inspired from FRC
= VT + IRV
requires effort
vital capacity
volume of gas maximally inspired from RV
= ERV + VT + IRV
- requires effort
define total lung capacity
estimated from?
effort or passive?
total volume of gas in lung
= RV + ERV + TV + IRV
- requires effort
–> estimated from RV
define flow equation
flow = volume/time
what is an acceptable measure of expiratory airflow
6 sec expiratory time
curve plateaus for ~ 1 sec
when you are measuring airflow, you are measuring ____
expiratory airflow
Reproducibility of airflow means you need to have
3 FEV1 maneuvers within 200 mL
Define FEV1
within 1st second after expiring
70-80% should come out within first second
Define FVC
FVC = forced vital capacity
should be same as vital capacity
Define FEV1/FVC ratio
what is normal range
ratio between the amount of air expire d in 1st second to entire expired amount
0.7-0.8 dependent on age
if you have airflow obstruction, how does that affect FEV1/FVC
then FEV1/FVC ratio decr
what is HALLMARK OF OBSTRUCTIVE LUNG DISEASE
reduced FEV1/FVC
what do values of FEV1/FVC ratio dependent on?
1) age, gender, race, height
normal range = 80-120%
if the FEV1 is greater or FEV1/FVC incr than what you would expect, suggestive of?
suggestive of restrictive process
cannot diagnose restrictive disease on spirometry MUST HAVE LUNG VOLUMES TO DIAGNOSE
what is the flow-volume loop?
airflow vs. amount of air expired
expiratory limb = positive deflection
inspiratory limb = negative deflection
shape of inspiratory limb?
symmetric
when you see obstructive lung disease on flow-volume loop what is characteristic?
when you see restrictive lung diseases on flow-volume loop what is characteristic?
reach peak expiratory flow rate, but obstructive so can’t get air out (high airway resistance) –> flow rate decr rapidly –> “coving” = cannot make a diagnosis just supportive
for restrictive diseases, normal shape to flow-volume curve, but at same volume, expiratory flow is higher (supranoral airflow)
if you have obstrictive outside the thorax (extrathoracic) what happens during expiration vs. inspiration
during expiration, you generate positive pressure in chest to blow air out
trachea surrounded by atmospheric pressure and positive pressure in lumen, so push walls of trachea apart during expiration
not see much obstruction to airflow
___
during inspiration, you have negative pressure in chest so in lumen of trachea you have negative pressure, and outside of trachea =
so trachea walls move in during inspiration
–> see truncation of flow-volume loop (flattening during inspiration)
if you have obstruction in central airway inside thorax (intrathoracic obstruction)
during expiration, airway surrounded by positive pressure in lung itself to move air out so airway has positive pressure outside compared to inside, so walls of trachea will move inward –> truncation of flow volume cloop
during inspiration, airway surrounded by negative pressure to pull airway walls out in the thorax so obstruction is not visualized on flow-volume loop
variable intrathoracic obstruction vs. variable extrathoracic obstructive vs. fixed obstruction
intrathoracic –> arrow points down (central airway tumors)
extrathoracic –> arrow points up (laryngospasm, laryngeal edema)
fixed –> doesn’t change with inspiration vs. expiration
Lung Volumes with Helium Dilution Method
1) inhale known concentration of inert gas (not absorbed into blood stream in alveoli = N2 and He)
2) allow diffuse
3) blow out and have C2 to calculate what volume of distribution that initial gas went into = gives you total lung capacity
what is plethysmography
measures lung volumes based on
P1 V1 = P2 V2
breathing around the functional residual capacity –> intermittently shutter will close =-> change in volume
HOW DO you measure compliance (dV/dP)
how well your lungs expand/how elastic or floppy are your lungs
1) probe into esophagus
2) inhale to TLC
3) exhale out, measure pressure
4) repeat
measure total volume you’ve exhaled out and plot against pressure change
pressure-volume change in disease
as you get more volume, it takes more pressure to get much smaller change in volume
