Diffusion Capacity Of Lung For Carbon Monoxide Methods and Normal Values

1. DLCO
Dr Athul Francis
JR-II
Pulmonary Medicine

2. DLCO-Measures the efficiency of lung in transporting oxygen
across the alveolar capillary membrane
Also known as Transfer Factor
measurement of CO uptake reflects a no. of processes(not
just diffusion) and it submaximal values ,hence its not truly
a capacity
Assessment of gas exchanging ability of the lung

3. Carbon Monoxide Diffusing Capacity
 Transfer of Carbon Monoxide – Diffusion Limited
 Unit: ml of CO/minute/mm /Hg
 0 degree Celsius,760 mm Hg ,dry
 STPD-Standard Temperature Pressure Dry

4. Why is CO used ??
 CO combines with Hb about 210 times more readily than
oxygen
 Diffusion Limited transfer
 Limited/no CO in blood/alveoli

5. Components of Diffusion Pathway
Gas space within the alveolus
• Tissue barrier – alveolar capillary membrane
• Alveolar lining fluid – surfactant rich
• Plasma layer
• Diffusion into and within the RBC
• Uptake of CO by hemoglobin

7. 

8. 

9. Methods Of DLCO measurement
 1.Single breath Hold
 2.Rebreathing Method
 3.Intrabreath Method
 4.Steady State Method

10. Single Breath Hold –Modified Krogh’s
 Before Starting the procedure :
 A) Calibrate the equipment
 B) Enter the necessary Data
 C) Enter Hb levels
 Place the Subject in sitting Down Position
 Adjust the mouth piece to proper position
 Seal the lips firmly around mouthpiece

11. Indications
Most commonly used in evaluation of
 diffuse interstitial lesions
 suspected emphysema
 pulmonary vascular obstruction
 Monitoring of Drug Therapy –Amiodarone
Useful in diagnosis as well as follow up

12. Diffusing Capacity
DLcosb
Pretest Patient Preparation
Should refrain from:
Smoking for at least 24 hours prior to testing
Consuming alcohol 4 hours prior to test (will
reduce DLco)
Strenuous exercise before testing (effects
pulmonary capillary blood volume)
Eating for at least two hours prior to testing
(digestion effects pulmonary capillary blood
volume)

13. Diffusing Capacity
Pretest Patient Preparation
o Should sit for at least 5 minutes
before test (effects pulmonary
capillary blood volume)
o Supplemental O2 should be
discontinued at least five minutes
prior to testing

14. SINGLE BREATH METHOD
Breathing maneuvers reqd :
Tidal breathing for few breaths
Unforced expiration to RV
Single forced inspiration.
Breathhold for 8-12 sec
Rapid expiration

15. o Inspiratory gas mixture contain 0.3%CO and an inert gas
10%He.
o Rapid exhalation time of <4sec &sample collection of no
more than 3sec.are required.
o Initial portion of expirate containing dead space is
discarded ;remainder is collected & conc. of CO & He are
measured.

16. Procedure
Unforced exhalation to RV
(limited to 6 seconds)
Rapid inhalation of a diffusion gas mixture to TLC (from spirometer/demand
valve/reservoir)
0.3% CO
10% He (tracer gas)
21% O2
Balance Nitrogen
Breath hold at TLC for 10 +/- 2 seconds
Rapid exhalation
(should not exceed 4 sec)

17. Alveolar gas is collected after a washout volume
(0.75-1.0 L) has been discarded
(If VC is <2.0 L, washout volume may be reduced to 0.50L)
Sample gas volume should be 0.50 – 1.0 L
(If VC <1.0L, a sample of <0.50L can be analyzed if deadspace
volume has been cleared)
Sample is analyzed for the fractional CO and He (tracer gas)
concentration
Change in He concentration reflects dilution by gas in lungs at RV
This change is used to determine the initial CO concentration

18. Summary of the procedure
Spirometry, lung volumes

21. Acceptability Criteria
1.System has
passed calibration
and quality
control
2.Inspiration from
RV to TLC –rapid
and within four
seconds
3.Inspired
Volume-85 % of
recorded VC
4.Breath Hold
Time between 8-
12 seconds – no
leaks , no Valsalva
5.Rapid
Exhalation-lasting
4 or less seconds
6.Interval of 4
minutes between
two episodes

22. 7.TLC and Va is consistent with clinical finding.Tlc should be
always more than Va
8.Average of two or more tests should be reported
Duplicate values should be within 3ml/min/mm Hg of each other
or within 10 percentage of the largest value.

23. Average DLco value
20-30 ml CO/min/mm Hg (STPD)

24. Inspiratory maneuver
14%He, 18%O2, 0.27%CO)
breathhold
Deadspace washout(0.75
L)
If VC<2L, reduce to 0.5L
Sample collection
volume
0.5-1LIf VC<2L, reduce
to 0.5L

25. Calculation of
DLCO
DLCO = VA X ln FACOi
 T X (PB-47) FACOF
T = time of breath hold
PB = barometric pressure
47 = water vapour pressure at 37oC
KCO = DLCO
 VA
VA=alv.vol
FACOi=alv conc.@start of breath
holding.
FACOF=alv conc.@end of breath
holding

26. FACOi =FEHe/FIHe *FICO
FEHe=expired conc of He
FIHe=inspired conc of He
FICO=inspired conc of co
FACO final is equal to conc of co in expired gas.

27. Va alveolar volume is determined in 2 ways:
1)Sum of RV calculated by closed circuit He or body
plethysmography and vol of inspired gas as
recorded on spirometer.
2)Calculated from single breath dilution of He that
occur during determination of DLCO.

28. Equipment quality control
Gas-analyser zeroing Done before/after each test
Volume accuracy Tested daily
Standard subject or simulator testing Tested at least weekly
Gas-analyser linearity Tested every 3 months
Timer Tested every 3 months

29. Severity for diffusion disorders
% of predicted
Normal 80 – 100
Mild 60 – 79
Moderate 40 – 59
Severe 20 – 39
Very severe < 20

30. STEADY STATE METHOD
In this a gas mixture containing 0.1%CO is
breathed until the rate of CO uptake from
lung is constant.
It require no respiratory manuveres and can
be done during exercise.
It require Arterial blood sample.
It gives lower value for resting subjects than
single breath method.

31. Rebreathing Method
 Patient is made to rebreathe from a reservoir containing
0.3 % CO, tracer gas and air
 30-60 seconds at 30 breaths/min
 Final CO,tracer and O2 concentrations are measured.

32. Slow exhalation Single Breath
Intrabreath Method
 Patient inspires a VC breath of test gas containing 0.3 %
CO,21 % O2 and the balance N2
 Patient exhales slowly – 0.5L/sec from TLC to RV.
 CH4 used as the tracer gas

34. Normal values of DLCO and corrected
DLCO
 Normal Value: 20-30 ml CO/min/mm Hg
 Normal Value depends on :
 Age –decreases as age increases
 Sex-lower in females
 Size-taller people-larger lung –higher DLCO

35.  Alveolar volume-measured with the help of helium
 DLCO/Va –normalizes the DLCO for various sizes
 Also known as Krogh Constant

36. Corrected DLCO


37.  2.Correction for COHb : DLCO X (102 %-CoHb %)
 3.Correction for altitude and PAO2
 DLCO for altitude= DLCO /( 1+0.0031 {PiO2-150)
 PiO2=0.21X(Pb-47)
 Similar corrections are also done, in other
scenarios .

39. Factors Affecting DLCO
 1. Haemoglobin and Haematocrit
 1g/dl decrease in Hb –DLCO reduces by 4 percent
 1g.dl Increase in Hb – DLCO increases by 2 %
 2.COHb
 Smokers-increase CoHb- decrease DLCO
 Each 1% increase- 1% decrease in DLCO

40.  3.Alveolar PCO2
 Increased PCO2-Increases DLCO
 4.Pulmonary Capillary Blood Volume
 Directly propotional
 Increase CO-exercise
 Pulmonary Haemorrhage

41.  5. Body Position
 Supine –increases
 6.Altitude Above Sea Level :
 High altitudes-higher DLCO
 7.Asthma and obesity
 Increased DLCO
 Enough explanations not available

42. Conditions Increasing Diffusing Capacity
 Polycythemia
 Obesity
 Asthma –usually when symptom free
 Pulmonary hemorrhage
 Supine Position
 Exercise
 Left to Right Shunt

43. Conditions Lowering Diffusing Capacity
 Decreased area for diffusion:
 Emphysema
 Lung Resection
 Bronchial Obstruction by tumour
 Anaemia
 Multiple Pulmonary Emboli

44.  Increased thickness of alveolar capillary membrane
 IPF
 CCF
 Asbestosis, Sarcoidosis
 Collagen Vascular diseases
 Drug Induced-
Amiodarone,nitrofurantoin,bleomycin,methotrexate
 Hypersensitivity pneumonitis
 Histiocytosis X
 Alveolar Proteinosis

46. CASE 1
 55 year old woman was referred with complaints of
Breathlessness on exertion.
 Smoking history of 38 packs years ,stopped 6 months ago
 Patient also has history of early morning cough with
expectoration
 Height :165 cms
 Weight-62.3 kgs

47. Pre bronchodilator
PREDICTED ACTUAL % PREDICTED
FVC 2.89 2.77 96
FEV1 2.30 1.91 83
PEF 6.08 4.01 66
PREDICTED % PREDICTED % CHANGE
FVC 2.82 98 2
FEV1 2.01 87 5
PEF 5.13 84 28
POST BRONCHODILATOR

48. Predicted Actual %predicted
TLC 4.39 4.97 113
FRC 2.45 3.10 127
RV 1.58 2.20 139
VC 2.89 2.77 96
IC 1.94 1.87 96
ERV 0.87 0.90 103
RV/TLC 36 44

49. PREDICTED ACTUAL % PREDICTED
DLCOsb (ml
CO/min/mm Hg)
19.7 10 51
Va 18.1 10 55
DL/Va 4.49 2.51 46
Hb 11

50.  1) What is the interpretation of PFT and
DLCO reports ??
 2)What other tests can be indicated ?
 3) What is the treatment recommendation?

51.  INTERPRETATIONS :
 FEV1 AND FVC –Normal
 Post bronchodilation :minimal change in FEV1 and FVC
 INCREASED –FRC and RV
 RV/TLC-Increased – AIR TRAPPING
 DLCO AND DL/Va reduced-Obstructive process
 Impression:
 Mild Obstruction with minimal response to bronchodilator
 Air trapping as suggested by DLCO reports

52. References
 Interpretation of Pulmonary Function Tests-
Robert E Hyatt and Paul Scanlon
 Ruppel’s Manual of Pulmonary Function Testing
 Fishman’s Textbook of Pulmonary Medicine