lung volumes what are they good for? - cacpt · 2019-09-10 · ats/ers lung volumes • no one...

LUNG VOLUMESWhat Are They

Good For?

Gregg L. Ruppel, MEd, RRT, RPFT, FAARCAdjunct Professor, Pulmonary, Critical Care & Sleep Medicine

Saint Louis University Hospital

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?

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)

Low FVC = Restriction

Aaron SD et al., Chest 1999; 115:869-873

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

FVC, FEV6 and Restriction

Non-obstructedmales

females

Obstructedmales

females

Vandevoorde et al. Eur Resp J 2008

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)

How Important Is A Low TLC?

• FVC - TLC relationship

• “Non-specific” ventilatory impairment

• Mixed obstructive/restrictive disease

• FRC in obesity

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?)

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

Mixed Obstruction-Restriction

Very few obstructedsubjects have restriction

Dykstra et al, 1999

Adjusting Severity in Mixed Obstruction-Restriction

FEV1 %PREDadj = FEV1 %PRED / TLC %PRED

Gardner et al, Chest, 2011

Obesity, TLC and FRC

Jones et al,

2006

Exponential

decrease

Obesity (waist size) and FVC

Leone et al, 2009

40 inches 35 inches

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

RV in Healthy Subjects- NHANES III Caucasian subjects- ECCS lung volume equations

Quanjer et al, unpublished data

TLC in COPD & Asthma

Dykstra et al, 1999

Gray Zone

RV and RV/TLC in Obstruction

Dykstra et al, 1999

Gray Zone

Is IC all that is needed?

Casanova et al, 2005

IC/TLC Ratio

Is IC all that is needed?

Peak change552 ml Average change

IC 215 mlFEV1 198 ml

VanNoorde et al, 2006

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

965 COPD patients

McCartney et al, Resp Care, 2016

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

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$

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

Gas Dilution vs. Plethysmography

O’Donnell et al, 2010

Obstructed patients

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

Single vs. multiple breath dilution

Milite et al, 2009

Imaging for lung volumes

• Accurate? Yes, but poorly standardized

• Cost? $$$

• Risks? Low dose ionizing radiation

Eisenberg et al, 2011

Fazel et al, 2009

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

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

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

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

Questions ?

Jupiter 7/9/2019