Diffusion Capacity: Indications and Interpretation | Jindal Chest Clinic

1
Diffusion CapacityIndications and
interpretation

• Surinder K. Jindal
• (Emeritus Professor, Pulm Med, PGIMER,
  Chandigarh)
• Medical Director, Jindal Clinics, Chandigarh
• www.jindalchest.com

2
Mechanisms of gas-exchange from air to tissues
3
Alveolo-capillary membrane
4
Diffusion 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.

5
DLCO estimation Single breath
6
Normal 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
  

7
Causes of abnormal values

• Decrease

• Increase

• 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

8
Severity classification of DLCO

• Normal gt75 of predicted, up to 140
• Mild decrease 60 to 74
• Moderate decrease 40 to 59
• Severe decrease lt40

9
Indications

• Evaluation

• Follow-up assessment

• 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

10
Other 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)

11
Interpretation

• 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

13
Clinical 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

15
Drug-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

16
Clinical 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.

17
Clinical 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?

18
DLCO 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

19
Pitfalls of DLCO

• Technical

• Clinical Interpretation

• 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.

20
Conclusions

1. 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.
2. Reduced DlCO in the context of normal spirometry,
   lung volumes, and chest radiographs suggests
   underlying lung disease such as ILD, emphysema,
   or PAH.
3. 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

• THANK YOU