20. Bronchodilator Response
Degree to which FEV1 improves with inhaled
bronchodilator
Documents reversible airflow obstruction
Considered a significant response if:
- FEV1 increases by 12% and >200ml
Request if obstructive pattern on spirometry
27. Diffusing Capacity
Diffusing capacity of lungs for Carbon Monoxide
Measures ability of lungs to transport inhaled gas
from alveoli to pulmonary capillaries
Depends on:
- alveolar—capillary membrane
- hemoglobin concentration
- cardiac output
29. DLCO — Indications
Differentiate asthma from emphysema
Evaluation and severity of restrictive lung
disease
Early stages of pulmonary hypertension
Pre-operative assessment: < 60% correlates to
poor prognosis following lung resection
Not done for routine evaluation or follow-up, it’s
expensive
30. Bronchoprovocation
Useful for diagnosis of asthma in the
setting of normal pulmonary function tests
Common agents:
- Methacholine and Histamine
Diagnostic if ≥20% decrease in FEV1
31. Quick Reference Obstructive Disease Algorithm
↓
SYMPTOMS
PFTs
OBSTRUCTION?
YES NO
TREAT
BRONCHOPROVOCATION
Obstruction
TREAT
No Obstruction
Other Diagnosis
↓
↓
↓ ↓
↓
↓ ↓
32. Interpretation
What is the clinical concern?
What is “normal” or “baseline”?
Did the test or equipment meet American
Thoracic Society (ATS) criteria?
Don’t forget to look at the flow volume loop.
36. PFT Patterns
Asthma
FEV1/FVC normal or decreased
DLCO normal or increased
PFTs may be normal bronchoprovocation test
37. Question
Which of the following is used to follow disease severity in
COPD patients?
a. Total lung capacity (TLC)
b. Degree of responsiveness to bronchodilators
c. Forced vital capacity (FVC)
d. Forced expiratory volume in 1 second (FEV1)
e. Diffusing capacity (DLCO)
38. Answer
Which of the following is used to follow disease severity in
COPD patients?
a. Total lung capacity (TLC)
b. Degree of responsiveness to bronchodilators
c. Forced vital capacity (FVC)
d. Forced expiratory volume in 1 second (FEV1)
e. Diffusing capacity (DLCO)
39. Question
A 36yo F, non-smoker, presents to your office for follow-up of
‘recurrent bronchitis.’ You suspect asthma and decide to
order spirometry. Which of the following would you
include in your prescription for testing?
a. Diffusing Capacity (DLCO)
b. If no obstruction present, perform trial of bronchodilator
c. If no obstruction present, perform methacholine challenge
d. Flow volume loop
e. b and c
40. Answer
A 36yo F, non-smoker, presents to your office for follow-up of
‘recurrent bronchitis.’ You suspect asthma and decide to
order spirometry. Which of the following would you
include in your prescription for testing?
a. Diffusing Capacity (DLCO)
b. If no obstruction present, add trial of bronchodilator
c. If no obstruction present, perform methacholine challenge
d. Flow volume loop
e. b and c
41. Question
A 68yo M is admitted to the ICU with acute respiratory
distress. A CXR obtained in the ED demonstrates
bilateral pulmonary infiltrates, and his DLCO is
elevated. What is the most likely diagnosis?
a. Pulmonary edema
b. Aspiration pneumonitis
c. Pulmonary emboli
d. Alveolar hemorrhage
e. Interstitial lung disease
42. Answer
A 68yo M is admitted to the ICU with acute respiratory
distress. A CXR obtained in the ED demonstrates
bilateral pulmonary infiltrates, and his DLCO is
elevated. What is the most likely diagnosis?
a. Pulmonary edema
b. Aspiration pneumonitis
c. Pulmonary emboli
d. Alveolar hemorrhage
e. Interstitial lung disease
43. References
1. Aboussouan LS, Stoller JK: Flow volume loops. UpToDate, 2006.
2. Bahhady IJ, Unterborn J: Pulmonary function tests: an update. Consultant.
2003.
3. Barreiro, TJ, Perillo I: An approach to interpreting spirometry. Am Fam
Physician. 2004 Mar 1;69(5):1107-14.
4. Chesnutt MS, Prendergast TJ. Current Medical Diagnosis and Treatment.
New York: Appleton and Lange, 2006.
5. Enright PL: Diffusing capacity for carbon monoxide. UpToDate, 2007.
6. Enright PL: Overview of pulmonary function testing in adults. UpToDate,
2007.
7. Irvin CG: Bronchoprovocation testing. UpToDate, 2006.
8. West JB. Respiratory Physiology: The Essentials. Lippincot Williams &
Wilkins, 2000.
Editor's Notes
The 6min walk test is great to evaluate physical function and can be used to assess therapeutic response in COPD and idiopathic pulmonary fibrosis (IPF) patients. If oxygen sats fall by &gt;4% (ending below 93%), this indicates significant desaturation, and need confirmatory ABGs.
Maximum respiratory pressures are used to identify a neuromuscular cause of restrictive lung disease.
Simple and complex cardiopulmonary exercise testing will not be addressed in this lecture.
Preop assessment is rarely to tell surgeon not to operate, but to prepare for pulmonary complications such as pneumonia, prolonged mechanical ventilation, etc. Also for screening: this includes all current and former smokers &gt;45yoa, known COPD or asthma pts, also those scheduled for thoracic or upper abdominal surgery. If mod-severe obstruction identified and surgery can be delayed, can start prophylactic program of pulmonary hygiene, stop smoking, give inhaled bronchodilators or steroids, etc.
Image source: http://www.spirxpert.com/index.html
FEV1 is decreased out of proportion to FVC, which causes the ratio to decrease as well.
This is not a complete list, just some of the most common diseases that should be on your differential for obstructive lung disease.
Image source: http://www.spirxpert.com/index.html
FEV1 decreases in proportion to decrease in FVC, so ratio remains normal or even slightly increased
Restrictive lung disease is made up of intrinsic lung disease (causes inflammation and scarring (interstitial lung diseases) or fill the airspaces w/ debris, inflammation (exudate); extrinsic causes are chest wall or pleural diseases that mechanically compress the lung and prevent expansion. Neuromuscular causes decreases ability of respiratory muscles to inflate and deflate the lungs.
Lack of observed response to bronchodilator does not preclude use, b/c patients may have symptomatic benefit.
Can give 6-8wk trial of bronchodilator and/or inhaled corticosteroids (ICS) and reassess clinically, can also obtain FEV1 at that time.
HOLD MDI THE MORNING PRIOR TO TESTING.
Have patient breath out at max effort, then breath in quickly at max effort, creates a loop w/ differing patterns.
Upper airway = pharynx, larynx, trachea.
Image source: http://www.nationalasthma.org.au/html/management/spiro_book/index.asp
Vocal cord dysfunction: variable extrathoracic obstruction.
Tracheal stenosis: fixed obstruction (hx frequent intubations).
Rapid rise to peak flow rate, followed by fall in flow as pt exhales toward residual volume. Inspiratory curve is symmetrical.
Example of someone grabbing trachea—causes problems w/ inspiration and expiration = fixed obstruction
Vocal cord dysfunction: variable extrathoracic obstruction.
Endobronchial carcinoma: variable intrathoracic obstruction. (Rare to diagnose this on flow volume loop).
FVC is decreased in both obstructive and restrictive disease, so usually need to obtain lung volumes to see if restrictive component present (increased TLC).
Measure of gas exchange at alveolar-capillary membrane.
Changes in DLCO are one of the earliest signs of interstitial lung disease (ILD).
Pulmonary vascular disease = pulmonary emboli, pulmonary HTN.
Low DLCO is also a major predictor of desaturation during exercise.
So you have restrictive disease by spirometry and lung volumes. You get a DLCO and see it is normal. Thinking back to your differential diagnosis of restrictive lung disease (what are the four things on your differential?), what can you probably rule out? Answer = Interstitial lung disease.
This is where you would order max respiratory pressures, to evaluate for NM disease. Max inspiratory pressures are recorded as patientt is breathing through a blocked tube, also done for expiration. Should be decreased in NM disease.
Can always send patient home and tell them to come back when having symptoms, but this delays diagnosis. Another alternative is measure peak flow variability at home.
If suspected asthma but has not responded to therapy, think of obtaining flow volume loop to see if there is vocal cord dysfunction = variable extrathoracic obstruction.
Now we’re going to put it all together…
Don’t need a DLCO, but if were decreased would make you think emphysema, if normal then chronic bronchitis.
IF restrictive pattern, you’re going to want to get DLCO b/c it tells you whether the restriction is due to parenchymal disease (which will change your management), or NM, pleural or CW disease
Remember that DLCO should be normal in chronic bronchitis because it affects the more proximal airways which is not where your gas exchange takes place.
In COPD patients, the FEV1 is used to classify severity of obstructive lung disease, and followed to assess progression.
This is kind of tricky b/c technically the recommendation is if no obstruction, then no bronchodilator (can omit this since costs an extra $40-50). Flow volume loops will usually come w/ your testing but you need to ask if you want the full max inspiratory and expiratory curves.
Intrinsic lung diseases that cause inflammation or scarring of the lung tissue OR that fill the airspaces w/ exudate or debris (pneumonitis or pneumonia) can cause decreased lung volumes and DLCO but NOT increased DLCO. This only comes from blood in the alveoli, polycythemia, L to R shunt or possibly asthma. So if you see bilateral pulmonary infiltrates on CXR and you get a DLCO that is elevated, then there is only one answer alveolar hemorrhage.