This document provides information on DLCO (diffusion capacity of the lung for carbon monoxide), a test used to evaluate how well oxygen passes from the alveoli into the blood. It describes how DLCO is measured using CO and calculates diffusion capacity based on CO uptake. Factors that influence DLCO levels are also discussed, including hemoglobin concentration, oxygen levels, body position, exercise, and lung volume. Decreased DLCO can indicate obstructive lung diseases, interstitial lung disease, and other conditions, while increased DLCO may be seen in polycythemia and pulmonary hemorrhage. The single-breath method is described as the most common technique for measuring DLCO.

1. DLCO Date :09/06/15
Presentation on DLCO
Dr. ANU K.N

2. DLCO Date :09/06/15
DLCO
Diffusion capacity of lung for CO
A Test to determine the extent to which O2 can pass from
alveoli to blood across the alveolar-capillary membrane

3. DLCO Date :09/06/15
DIFFUSING CAPACITY(DL)
Volume of gas diffusing through the resp membrane per min
per mm Hg difference in partial pressure of gas on the 2 sides
of the membrane
Directly prop to-Surface area of resp membrane & solubility of
the gas
Indirectly to thickness of membrane & molecular wt. Of the
gas

4. DLCO Date :09/06/15
Measurement of diffusion capacity
1)O2
DLO2=˙VO2/PaO2− PcapO2
V- volume of O2 absorbed by pulmonary blood per unit time
PaO2-alveolar O2 conc.
PcapO2-pulm cap O2 conc
DL for O2=21 ml/mt/mmhg
Very difficult to measure:Ventilation-Perfusion mismatch,Shunting& because
PcapO2 has changing values during capillary transit.
hence DLO2 is measured indirectly with DLCO

5. DLCO Date :09/06/15
2) DLCO
Good alternative:
>CO present in negligible amounts in blood.
Hence,DLCO=VCO/PaCO-PcapCO
=VCO/PaCO
>CO binds to Hb in the same manner as O2
>Transfer is diffusion limited,not perfusion limited
Normal DLCO-20-30ml/mt/mmHg

6. DLCO Date :09/06/15
Roughton and Forster
• 1/DLCO= 1/DmCO+ 1/θCOVc
* DmCO = the diffusing capacity of the alveolar-capillary
membrane for CO
* θCO = the rate of displacement of O2 from intracellular
hemoglobin by CO
* Vc = the volume of blood in the pulmonary capillary bed

7. DLCO Date :09/06/15
Measurement of Dm and Vc
• Using values of θCO measured in vitro and values of DLCO
determined with different inspired O2 concentrations, membrane
diffusing capacity (DmCO) and capillary blood volume (Vc) can be
calculated
• DmCO under resting conditions is 75 to 100 ml/min/mmHg in men

8. DLCO Date :09/06/15
DLNO
>Binds to Hb in the same manner as O2
>Rate of binding very rapid
>DLNO assumed to be = to DmNO
>NO reacts with O2,has potential CVS side effects,DLNO needs
special equipment for analysis..used only for research purposes

9. DLCO Date :09/06/15
Methods for Measuring the Diffusing
Capacity
• Single breath method –most commonly used
• steady-state method - performed in subjects who are exercising
• rebreathing method- requires rapid responding gas analyzers and
high technical requirements

10. DLCO Date :09/06/15
SINGLE BREATH METHOD- 5 Steps
• 12 hours of abstinence from smoking is advisable
> Tidal breathing (no deep breaths)
> Unforced exhalation to Residual Volume (RV)
> Rapid Inhalation (< 4 seconds)from a gas mixture.
– 0.3% CO
– 10% He (tracer gas)
– 21% O2
– Balance Nitrogen
> Breath-hold period (9-12 seconds)
> Smooth, unforced, without hesitation
exhalation (< 4 seconds )

11. DLCO Date :09/06/15
• Discard volume 0.75 – 1 L (dead space)
• Sample volume 0.5 – 1 L (alveolar)
• Sample collection time<3sec
• Sample is analysed for tracer gas conc & fraction of CO, Change in
He concentration reflects dilution by gas in lungs at RV,This change
is used to determine the initial CO concentration
• Test repeated after 4 mins

12. DLCO Date :09/06/15
Time
10 s
Volume
RV
TLC = VA
Sample of alveolar gas

13. DLCO Date :09/06/15
• Perform at least 2 tests but not more than 5 tests (5 tests will
increase COHb by ~ 3.5% which will decrease the measured DLCO
~ by 3 - 3.5%)
• Testing is complete when two measurements agree within 3.0
ml/min/mmHg or within 10 percent of the higher measured value
• DLCO is reported as average of at least two acceptable tests

14. DLCO Date :09/06/15
CALCULATION OF DLCO
DLCO = 60 Va x FaCOi
T x (PB-47) FaCOF
T = time-period of breath hold
PB = barometric pressure
47 = water vapour pressure at 37◦c
Va = alveolar volume of gas(ml STPD)present
in lung at start of breath-hold
FaCO = alveolar fraction of CO at initial and
final times of breath-holding period

15. DLCO Date :09/06/15
• Va = Vi x FiHe/FaHe
• Vi =inspired volume
• FiHe=He conc in inspired air
• FaHe =He concentration in the expired alveolar gas sample

16. DLCO Date :09/06/15
Limitations
• requires patient cooperation to perform the necessary respiratory
maneuvers
• patient with reduced lung volume may not have a vital capacity
enough to clear the dead space to provide sufficient gas sample
• hold the breath for 10 s limits applicability in some patients
• can be employed only in the resting state

17. DLCO Date :09/06/15
FACTORS INFLUENCING DLCO
• Hb concentration.
• Alveolar partial pressure of O2
• Body position.
• Exercise
• Lung volume
.

18. DLCO Date :09/06/15
(1) Hb level
DLCO directly correlates with Hb
>1g/Dl decrease Hb – 4% decrease DLCO
> 1g/Dl increase Hb – 2% increase DLCO

19. DLCO Date :09/06/15
Predicted DlCO (Corrected)
Men
= Observed DLCO (1.7 Hb)/10.22 + Hb
Women
= Observed DLCO(1.7 Hb)/9.28 + Hb

20. DLCO Date :09/06/15
COHb level
Increase in COHb reduces DLCO in two ways
❖ decreases available binding sites on Hb
❖ reduces differential driving across ACM
1% Increase in COHb decreases DLCO by 1%

21. DLCO Date :09/06/15
(2)Alveolar Partial Pressure of Oxygen
>increased alveolar PO2 will reduce measured DlCO
>DlCO will be lowered if patients receive
supplemental oxygen during measurement
>reduced alveolar PO2 will lead to an increment in
measured DlCO

22. DLCO Date :09/06/15
(3)Body Position
DlCO is 5 to 15 percent greater in supine
position than in the erect position
• Blood volume shifts from the lower trunk and
legs to the lungs in the supine position,leads
to increase in Vc
• there is minimal increase in DmCO in the
supine position
• effect of posture on DlCO decreases with age

23. DLCO Date :09/06/15
(4)Exercise
• DlCO can increase twofold during exercise
• Both alveolar-capillary surface area(Dm) and
capillary volume(Vc) are recruited by the
increase in cardiac output that accompanies
exercise

24. DLCO Date :09/06/15
(5)Alveolar volume:
DLCO decreases with decrease in alveolar
volume

25. DLCO Date :09/06/15
Uses
• DlCO provides a mean of assessing overall oxygen transport but does not
indicate specific defects in gas exchange

26. DLCO Date :09/06/15
INDICATIONS
• ILD-- initial evaluation ,response to treatment,referral for
transplantation
• Airway obstruction
• Before lung resection
• Disability evaluation in severe COPD/ILD
• Need for O2 therapy
• Alveolar hemorrhage

27. DLCO Date :09/06/15
DECREASE IN DLCO
• Obstructive Lung Diseases
–Emphysema
–Cystic Fibrosis
• Parenchymal Lung Disease
–Interstitial Lung Disease
• Idiopathic
• Asbestosis,
• Allergic alveolitis
• Drug induced

28. DLCO Date :09/06/15
• Pulmonary involvement in systemic disease
– SLE
– Progressive systemic sclerosis
– Mixed connective tissue disease
– Rheumatoid arthritis
– Dermatomyositis
– Polymyositis
– Wegeners granulomyositis
– Inflammatory bowel disease

29. DLCO Date :09/06/15
• Cardiovascular disease
– Pulmonary edema
– Pulmonary thrombo-embolism
– Primary pulmonary hypertension
– Acute myocardial infarction
– Fat embolization
• Others
– Anemia
– Chronic renal failure
– Marijuana smoking
– Acute and chronic ethanol ingestion
– Cigarette smoking
– Bronchiolitis obliterans with organizing pneumonia

30. DLCO Date :09/06/15
INCREASE IN DLCO
• Polycythemia
• Pulmonary hemorrhage
• Increased pulmonary blood flow
Left to right intracardiac shunts
• Exercise
• Pseudo increase-Br Asthma

31. DLCO Date :09/06/15
Obstruction and ↓DLCO
-> Cystic fibrosis
-> Alpha 1 antitrypsin deficiency
-> Bronciolitis obliterans
-> Lymphangiomyomatosis

32. DLCO Date :09/06/15
↓lung volume,↓DLCO
• Seen in Interstitial Lung Diseases

33. DLCO Date :09/06/15
↓DLCO,normal lung volumes
Seen in extrapulmonary restrictive lung disease
• Obesity
• Pleural effusion/thickening
• NM weakness
• Kyphoscoliosis

34. DLCO Date :09/06/15
↓DLCO,↓lung volume ,small airway
obstruction
• Miliary TB
• Sarcoidosis
• Asbestosis
• CCF

35. DLCO Date :09/06/15
Isolated fall in DLCO(normal spiro)
• Pulmonary vascular diseases
Eg. Chronic rec.pul. Emboli
Idiopathic PAH
Connective tissue
disorders/vasculitides
• ↑COHb level
• Early ILD

36. DLCO Date :09/06/15
Thank You