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
you cannot diagnose ___ on spirometry
restrictive diseases
what is the flow-volume loop?
airflow vs. amount of air expired
expiratory limb = positive deflection
inspiratory limb = negative deflection
define effort-independent portin of flow-volume loop
1) when expire, rapidly reach resp flow rate
2) effort indepedent = leftover 2/3 of expiration
because only maximal flow rate through airway no matter how hard you try
what is special about effort independent
no matter how hard you try you can’t incr this
linear decline in flow
determined by elastic recoil of lung and airways resistance
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
airflow interpretation what to look at?
how do you interpret?
- FEV1
- FVC
- FEV1 /FVC
- Flow-volume loop
–> decide if normal, obstructed, suggested restriction, airway obstruction
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
LIMITATIONS OF HELIUM DILUTION METHOD
in obstructive disease, if you have trouble getting air out, so you retain more gas –> lots of deadspace –> s inspird gas can’t distribute evenly (UNDERESTIMATE VOLUME)
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
benefits of plethysmography vs
cons = difficult, harder to do
pros= Most accurate as does not require diffusion of gas - important in patients with air trapping such as asthma and emphysema!
when interpreting lung volumes procedure
1) look at TLC
low = diagnostic of restrictive lung disease
2) look at FRC= thoracic gas volume
3) increased FRC (TGV) = hyperinflated
- TLC or FRC > 120%
RV > 140% (RV calculated)
if just RV elev then air trapping = obstructive
4) decr FRC = restricted)
- TLC or FRC < 80%
if you are hyperinflated what is your TLC or FRC
- TLC or FRC > 120% predicted
- RV >140% (RV is a calculated value)
- Air trapping if just RV elevated
what is DLCO
what is it determined by (4)
marker of gas-exchange
1) surface area of alveolar capillary interface
2) membrane thickness
3) diffusion gradient of gas
4) presence of Hb
where is gas exchange occurring?
alveolar-capillary interface
how do you measure DLCO
what does it mean?
1) inhale known concentration of CO
CO = 200x greater affinity for Hb so readily taken into blood stream from alveoli
2) hold for 10 sec
3) exhale so amount leaving is inversely proportional to how well alveoli working
more CO out (little taken up, so poor alveoli function)
3) also do helium diluton method to measure volume of distribution at same time
if you have decr DLCO what does that mean?
emphysema = destroy alveolus and capillary membrane so decr surface area –> dead space
interstitial lung disease or fibrosis –> incr membrane thickness (so CO uptake decr)
pneumonia or pulm edema –> alveoli filled with pus –> decr surface area, incr diffusion distance
pulm vascular disease –> in pulm HTN, incr resistance to flow so decr diffusion capacity and decr pulm blood flow –> decr DLCO
if you have incr DLCO what does that mean?
1) alveolar hemorrhage =
extrude RBC into alveoli –> Hb in lung –> CO bind all Hb –> incr DLCO
2) polycythemia
3) interstitial edema (water get into alveoli and interstitium full of water so more RBC)
4) asthma
hallmark of pulm vascular disease
normal airflow, normal lung volume
decr DLCO
why do you use helium dilutation with DLCO?
calculate alvoelar volume –> corrected for chest wall/pleural diseases (obesity) or resection of lung
lung resected due to lung cancer, amount of CO taking up will be decr because less surface area but not due to problem with alveoli
NOT CORRECT FOR RESTRICTIVE LUNG DISEASE WITH IDIOPATHIC PULM FIBROSIS BECAUSE IT AFFECTS DIFFUSING DISTANCE (ALVEOLAR MEMBRANE)
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
how does pulm fibrosis appear on pulm volume curve
pulm fibrosis = make lung like concrete –> pressure-volume curve is flatter so takes much more pressure for a given volume change
how does emphysema look on pressure-volume curve?
emphysema –> decr elastic recoil so lungs have been overstretched
much more compliant and get much larger volume change for given change in pressure (shift left and up)
obesity pressure-volume curve
obesity = more soft tissue around chest cavity, chest cavity = lower volume for given pressure
shifts curve down but no change in shape
asthma pressure-volume curves
asthma acute exacerbation = problem getting air out = retain more air in chest, more volume in lung at give pressure, shifted up
when do you see compliance measured?
ARDS with mechanical ventilator
giving known tidal volume
we can pressure at end of expiration to see compliance of lung
what is respiratory muscle strength
how much force generated on inspiration or expiration
PiMax:
• inspiration attempt against closed valve
- PeMax:
- expiration against closed valve
very effort dependetn so can fake it
Respiratory muscle weakness causes
1) neuropathies
2) myopathies
how to measure airway responsiveness with bronchodilator challenge
criteria
1) give albuterol (b2 agonist = vasodilator)
>12% change in FEV1 and/or FVC
and 200CC incr volume
how to measure airway responsiveness with methacoholine challenge
PC20 < 8 mg/mL
cholinergic medication –> bronchoconstriction
20% decr in FEV1
how to measure airway responsiveness with EIB
1) inhale cold air while exercising
2) want to see decline in FEV1 by 20% to be positive
procedure of looking at all PFTs
1) look for airflow obstruction
- present/absent
- bronchodilator response
2) lung volumes (incr, decr, mixed = airflow obstruction + decr lung volume)
3) gas exchange (DLCO and DLCO/VA incr/decr/normal)
4) flow volume loop (upper airway obstruction)
FEV1 = 2.29L 72% predictive
FVC = 6.04
FEV1 incr to 2.63L 83% predictive
FEV1 = 2.29L 72% predictive
FVC = 6.04
Ratio of FEV1/FVC = low
gets bronchodilator
FEV1 incr to 2.63L 83% predictive (>200 cc change in FEV1 so he has reversibility)
FEV1 = 44%
FVC = 44%
ratio preserved at 88%
TLC = 92% predictive
FRC reduced and RV reduced (less than 80%)
Adjusted DLCO/VA = 112%
symmetrically reduced
suggests restrictive lung disease but can’t diagnose with spirometry
TLC = 92% predictive = restrictive lung disease
FRC reduced and RV reduced (less than 80%)
DLO 46% predictive
Adjusted DLCO/VA = 112% so restriction not due to parenchymal lung disease but some chest wall
restrictive lung disease with normal DLCO/VA
obesity, pleural disease, or neuromuscular disease
FEV1 = 52%
FVC = 60%
Ratio = 66% (low = obstruction)
TLC = 77% (low)
RV and FRC = normal
DLCO = 41%
Ratio = 66% (low = obstruction)
TLC = 77% (low)
RV and FRC = normal = obstructive because give larger lung volume and restrictive causes lower lung volume so balance out
DLCO = 41% correct up to 83% with DLCO/VA
DLCO/VA adjusted and TLC should be within 500cc –> underestimated due to restrictive lung disease
–> restriction + obstruction
you can only say diffusing capacity reduced not chest wall obstruction
–> mixed disease with normal DLCO/VA
= obesity + COPD
