Title: Diffusion Capacity: Indications and Interpretation | Jindal Chest Clinic
1Diffusion CapacityIndications and
interpretation
- Surinder K. Jindal
- (Emeritus Professor, Pulm Med, PGIMER,
Chandigarh) - Medical Director, Jindal Clinics, Chandigarh
- www.jindalchest.com
2Mechanisms of gas-exchange from air to tissues
3Alveolo-capillary membrane
4Diffusion Capacity
- Misnomer It is not merely diffusion of gases
it is uptake of oxygen by RBCs in the capillary
blood. - It is not a lung capacity
- Preferred terminology Transfer Factor i.e.
transfer of oxygen from alveolar air to RBCs - Clinically it is assessed by using a gas
with low solubility in pulm membrane and high
capacitance in blood (binds to Hb) such as CO.
(O2 or NO are not routinely used)
- It is a test to measure diffusion of gases across
the alveolo-capillary membrane.
5DLCO estimation Single breath
6Normal DLCO - Determinants
- Resting level 20-30 mL/min/ mmHg
- Normal variations
- Age
- Sex
- Height, weight
- Alveolar volume
- Ethnicity
- Smoking (decreases)
- Exercise (increases)
- Circadian rhythm
- Menstrual cycle
-
-
- 1. Area of the alveolo-capillary membrane
- alveolar surface and capillary blood
- 2. Thickness of the membrane
- 3. Driving pressure i.e. Difference of oxygen
tension between the alveolar gas and venous blood
7Causes of abnormal values
- COPD Emphysema
- Lung resection
- Bronchial obstruction
- Anemia
- Multiple Pulm emboli
- Thickened aveolo-capillary membrane
- ILDs - IPF
- Exercise
- Asthma
- Obesity
- Polycythemia
- L to R intra-cardiac shunts
- Alveolar hemorrhage
8Severity classification of DLCO
- Normal gt75 of predicted, up to 140
- Mild decrease 60 to 74
- Moderate decrease 40 to 59
- Severe decrease lt40
9Indications
- Parenchymal diseases
- IPF
- H.P, CTD lung disease
- Pneumoconioses
- Sarcoidosis
- Emphysema
- Pulm vascular diseases
- Systemic diseases
- Interstitial infections
- Alveolar Hmge
- Drug pulm- toxicity
- Severity assessment
- Disease progression
- Treatment efficacy
- Parenchymal lung diseases IPF
- COPD Emphysema
- Pulm drug toxicity
10Other uses of DLCO
- DLCO is a specific but insensitive predictor of
abnormal gas exchange during exercise. Low DLCO
less than or equal to 50 predicted can predict
hypoxemia with exercise. A normal DLCO does not
rule out oxygen desaturation with exercise. - A decrease in DLCO in persons with HIV
independently predicts the development of
opportunistic pneumonia - In the setting of a normal chest radiograph,
early ILD or pulmonary vascular disease or both
can be present. - A DLCO below 30 predicted is required by Social
Security for total disability (USA)
11Interpretation
- DLCO is the product of two primary components
- i. Surface area of the lung available for gas
exchange (VA) - ii. Rate of alveolar capillary blood CO uptake
(KCO) - It is always important to determine whether the
reduction in DLCO is due to reduction in VA or
KCO or both. - DLCO can be falsely reduced in patients with
severe COPD or severe restrictive lung disease
when the inspired CO does not completely reach
the functioning alveolo-capillary units.
12- Interpretation is step-wise progress
- Look at DLCO reduced by either a decrease in VA
- or KCO we need to
look for both - components
- 1. Remember DLCO VA X KCO and
- KCO DLCO / VA
- 2. Look at VA within 5 of TLC If not, suspect
loss of lung volume (collapse, resection, NM
diseases, embolic disease) DLCO reduced
proportionately. - 3. Look at KCO (DLCO / VA) reduced in anemia,
ILD and pulm vascular diseases
13Clinical problem - 1
- 45 year old male
- No known lung disease
- On amiodarone for 6 mths for cardiac problem
- Now c/o non-productive cough, dyspnea, and weight
loss - Scattered crackles on physical examination
- Suspected to develop drug-induced ILD
- Lung function tests Normal spirometry
-
14- Abnormal chest radiograph showing chronic
interstitial lung changes. - DLCO 62 of predicted
-
- Diagnosis
- Amiodarone induced ILD
-
- Amiodarone stopped
- Improved after a week
-
15Drug-induced lung disease
- New or worsening symptoms or signs
- New abnormalities on chest radiographs
- Decline in TLC of 15 or more, or a decline in
DlCO of more than 20. - Chronic interstitial pneumonitis is the most
common form of drug-induced lung disease, - The condition may improve when the drug is
stopped, with or without adding systemic
corticosteroids
- Amiodarone
- Amphotericin,
- Methotrexate,
- Cyclophosphamide,
- Nitrofurantoin,
- Cocaine,
- Bleomycin,
- Tetracycline,
- Many newer biologics
16Clinical problem 2
- A 38 year old house-wife with history of asthma
since childhood multiple anti-asthma therapies
but poorly controlled - Normal CXR, spirometry and lung function. ECHO
revealed elevated PA pressure - DLCO unexpectedly reduced DLCO (35 predicted)
- Diagnosis difficult-to-control young adult
asthmatic woman with PAH ? COPD x - ?Drugs ?Secondary to CTD
- Detailed history revealed that she was on dieting
pills, methamphetamines. - The diagnosis was made after decreased DLCO
prompted a search for the reasons.
17Clinical problem 3
- A 54 year old shopkeeper mild smoker of over 25
years was following the Chest Clinic with
intermittent symptoms of breathlessness,
wheezing, cough and phlegm. - Chest showed increased AP diameter.
- CXR - mild hyperinflation
- Spirometry Moderate airways obstruction with
partial bronchodilatory responsiveness. - Diagnosis ? COPD ? Ch Bronchial Asthma
- How to confirm the diagnosis?
18DLCO in IPF
- Evaluation of abnormal gas exchange in early IPF
esp when spirometry is normal - Normal spirometry and disproportionately
low DLCO may indicate CPFE - 2. More reliable indicator of disease-outcome
than other resting lung function indices - i. DLCO of lt40 indicates advanced disease
- ii. Fall of gt15 from baseline value in 6-12
months - implies poor outcome and higher mortality
- iii. Should be performed every 6-12 months
19Pitfalls of DLCO
- May be normal in
- Early ILD PVD,
- Early COPD
- May be markedly reduced even in the presence
of a normal chest skiagram - May be abnormally high (140 or more) in Asthma,
polycythemia, obesity, L to R shunts, hemoptysis
- Lack of uniformity and standardization between
different laboratories - Lack of nomograms in India difficulty of
predicted norms - Routine reporting of DlCO corrected to normal
with VA is misleading and can cause
under-diagnosis when in fact DlCO still is
abnormal. - Difficulties of performance patients with
severe obstructive or restrictive dis. -
20Conclusions
- DLCO is an important PFT in the evaluation and
follow-up assessments of lung diseases A
decreasing DLCO is superior to following changes
in slow vital capacity (SVC) or TLC in ILDs. - Reduced DlCO in the context of normal spirometry,
lung volumes, and chest radiographs suggests
underlying lung disease such as ILD, emphysema,
or PAH. - DLCO should always be interpreted in the context
of clinical data of the individual patient
decrease or increase in DLCO is not diagnostic of
a particular lung disease
21