lung volumes what are they good for? - cacpt · 2019-09-10 · ats/ers lung volumes • no one...
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LUNG VOLUMESWhat Are They
Good For?
Gregg L. Ruppel, MEd, RRT, RPFT, FAARCAdjunct Professor, Pulmonary, Critical Care & Sleep Medicine
Saint Louis University Hospital
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4 Questions
1. Do lung volumes add to clinical decision making?
2. Is a low TLC (i.e. restriction) a useful measurement?
3. Do lung volumes tell us anything meaningful about obstruction?
4. Does it make any difference how you measure lung volumes?
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Physiology, physiology, physiology• Evidence-based grade for CPET in patients
with unexplained dyspnea = D*
• Evidence-based grade for TLC in patients with unexplained dyspnea = D**– non-specific but quantitative
– describes physiology, not disease
• FVC (or VC) commonly used to define ‘restriction’ (esp. chest wall abnormality)
* Palange et al: Recommendations on the use of exercise testing in
clinical practice. Eur Resp J 2007; 29:185-209.
** CUSLR (completely un-scientific literature review)
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Low FVC = Restriction
Aaron SD et al., Chest 1999; 115:869-873
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Glady et al, 2003
PFT Lab - SLUH
Spirometry
N=1678
FVC<85%
N=1015
FVC> 85%
N=663
FEV1/FVC <55%
N=131FEV1/FVC > 55%
N=884
Restriction?
884/1678 (53%)
Proceed to lung volumes
NHANES III
“Who Needs Lung Volumes” Algorithm
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FVC, FEV6 and Restriction
Non-obstructedmales
females
Obstructedmales
females
Vandevoorde et al. Eur Resp J 2008
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Lung Volumes (TLC)
may be indicated in:Asthma – restriction (Miller 2007)ILD (Boros 2004)Radiation/chemotherapy (Gopal 2003)Combined obstruction/restriction (Balfe 2002)Obesity (Watson 2010, Babb 2008)
not indicated in:Sarcoidosis (Boros 2010)
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How Important Is A Low TLC?
• FVC - TLC relationship
• “Non-specific” ventilatory impairment
• Mixed obstructive/restrictive disease
• FRC in obesity
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FVC → TLC Relationship • Normal FVC (VC) almost always excludes restriction
• TLC = FVC + RV
• TLC = FVC / (1 – RV/TLC)
y = 0.0028x + 0.1704
15%
20%
25%
30%
35%
40%
45%
50%
10 20 30 40 50 60 70 80 90
Neder (Brazil)
Roca (Spain)
Roberts (UK)
Goldman (S Africa)
ECCS (Europe)
Garcia-Rio (Spain)
Quanjer (NL)
Miller (US)
Mean
Linear (Mean)
RV/TLC in healthy Caucasians
(Predicting TLC from FVC?)
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Non-specific PFT pattern(Low FVC and FEV1, normal FEV1/FVC and TLC,
prevalence 4-10%)
Iyer et al, 2010
Hyatt et al, 2009
Follow up of
1284 NS patients
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Mixed Obstruction-Restriction
Very few obstructedsubjects have restriction
Dykstra et al, 1999
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Adjusting Severity in Mixed Obstruction-Restriction
FEV1 %PREDadj = FEV1 %PRED / TLC %PRED
Gardner et al, Chest, 2011
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Obesity, TLC and FRC
Jones et al,
2006
Exponential
decrease
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Obesity (waist size) and FVC
Leone et al, 2009
40 inches 35 inches
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Do lung volumes tell us anything meaningful about obstruction?
• RV (air-trapping) varies a lot in healthy subjects
• Air trapping in COPD and asthma
• IC – poor man’s FRC & beggar’s RV
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RV in Healthy Subjects- NHANES III Caucasian subjects- ECCS lung volume equations
Quanjer et al, unpublished data
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TLC in COPD & Asthma
Dykstra et al, 1999
Gray Zone
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RV and RV/TLC in Obstruction
Dykstra et al, 1999
Gray Zone
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Is IC all that is needed?
Casanova et al, 2005
IC/TLC Ratio
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Is IC all that is needed?
Peak change552 ml Average change
IC 215 mlFEV1 198 ml
VanNoorde et al, 2006
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That damned residual volume
2265 COPD patientsResponse to bronchodilator(10% or greater change) by GOLD stage
RV (pre BD)I 135±32%II 162±43%
III/IV 218±62%
Deesomchok et al, 2010
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965 COPD patients
McCartney et al, Resp Care, 2016
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Does it make any difference how you measure lung volumes?
• ATS/ERS guidelines
• Body plethysmography vs. gas dilution– Body box = gold standard?
– Body box overestimates lung volume in severe obstruction?
• Single vs. multiple breath dilution– Trapped gas?
• Imaging (CT) vs. traditional methods
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ATS/ERS Lung Volumes
• No one method recommended– Pleth produces larger volumes in obstructed
patients (panting at < 1 Hz advised)– Dilutional techniques may underestimate volumes in
obstructed patients
• VC, IC and ERV should be obtained by ‘linked’ maneuvers if possible
• CT compares favorably– May expose patient to high radiation dose– Breath holding at TLC may be a problem– Cost$
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Why pant at < 1.0 Hz?
Stanescu and Rodenstein, 1982
In the presence of obstruction:
1. Pm < Palv
2. Phase shift between Pm and Pbox
3. VTG is overestimated
4. 1 and 2 are frequency dependent
5. panting < 1 Hz minimizes effect
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Gas Dilution vs. Plethysmography
O’Donnell et al, 2010
Obstructed patients
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Milite et al, 2009
Gas Dilution vs. Plethysmography
Bias of 0.5 L,
but with little difference
due to severity of obstruction
(p for interaction = 0.25)
55 emphysema patients
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Single vs. multiple breath dilution
Milite et al, 2009
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Imaging for lung volumes
• Accurate? Yes, but poorly standardized
• Cost? $$$
• Risks? Low dose ionizing radiation
Eisenberg et al, 2011
Fazel et al, 2009
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Conclusions1. Do lung volumes add to clinical decision
making? – Not much for making specific diagnoses
– May be needed to resolve a low (properly performed) FVC
– TLC indicated only if it will help confirm/reject a diagnosis, or assist in planning therapy
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Conclusions
2. Is a low TLC (i.e. restriction) a useful measurement?
- If you know FVC, you know a lot about TLC
- Non-specific ventilatory pattern defined by a normal TLC
- TLC %Predicted may be helpful for adjusting severity in mixed disease
- FRC (but not TLC) is significant but variable in obesity
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Conclusions3. Do lung volumes tell us anything meaningful
about obstruction?- RV (upper limit of normal) is quite variable in
healthy subjects
- TLC, RV, and RV/TLC vary significantly in asthma and COPD when FEV1 is near LLN
- IC tells us a lot about hyperinflation but needs to be related to TLC (and RV)
- RV may be a useful index of response to bronchodilators in moderate/severe obstruction
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Conclusions4. Does it make any difference how you
measure lung volumes?- Maybe not as much as previously thought- Plethysmography probably overestimates lung
volumes in obstruction- Unclear how much dilutional methods
underestimate lung volumes in obstruction- Single breath dilutional volumes reflect severity
of obstruction- CT is expensive and increases radiation exposure,
but has become commonplace
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Questions ?
Jupiter 7/9/2019