1. RET 2414 Pulmonary Function Testing Module 4.0
Diffusing Capacity
RET 2414
Pulmonary Function Testing
Module 4.0

2. Diffusing Capacity Single Breath Method (DLcosb)
(Modified Krogh Technique)
DLco measures the transfer of a carbon MONOXIDE (CO) across the alveolocapillary membranes

3. ml of CO/minute/mm Hg (STPD)
Diffusing Capacity
DLcosb
CO combines with Hb 210 times more readily than O2
DLco is expressed as:
ml of CO/minute/mm Hg (STPD)
STPD (0 C, 760 mm Hg, Dry)

4. Diffusing Capacity DLcosb 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

5. Diffusing Capacity DLcosb Procedure
Breath hold at TLC for 10 +/- 2 seconds
Rapid exhalation
(should not exceed 4 sec)
Alveolar gas is collected after a washout volume ( L) has been discarded
(If VC is <2.0 L, washout volume may be reduced to 0.50L)

6. Diffusing Capacity DLcosb Procedure
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

7. Diffusing Capacity
DLcosb

8. NOT ! MEMORIZE ! Diffusing Capacity DLcosb DLcosb= VA x 60 x Ln FACO0
DLcosb is then calculated as follows:
DLcosb= VA x x Ln FACO0
(PB – 47) x (T) FACOT
NOT !
MEMORIZE !

9. Diffusing Capacity DLcosb Average DLcosb value
25 ml CO/min/mm Hg (STPD)

10. 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)

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

12. Diffusing Capacity DLcosb Acceptability Criteria
Volume-Time tracing should show smooth, rapid inspiration (<4 sec) from RV to TLC
Expiration should be rapid but not forced; 4 seconds or less

13. Diffusing Capacity DLcosb Acceptability Criteria
Dead space washout should be 0.75 – 1.00 L (0.5 L if VC is less than 2.0 L)
Alveolar sample volume should be 0.5 to 1.0 L
Inspired volume should be at least 85% of previously recorded best VC

14. Diffusing Capacity DLcosb Acceptability Criteria
Breath hold time should 10 sec +/- 2 sec (No Valsalva or Mueller maneuver)
The average of two or more acceptable test should be reported. Duplicate determinations should be within 10% of highest value or 3 ml CO/min/mm Hg

15. Diffusing Capacity DLcosb Decreased in: Significance and Pathology
Restrictive Lung diseases
Asbestosis
Berylliosis
Silicosis
Idiopathic pulmonary fibrosis
Sarcoidosis
Systemic lupus erythematosus
Scleroderma

16. Diffusing Capacity DLcosb Decreased in: Significance and Pathology
Inhalation of toxic gases (alveolitis)
Loss of lung tissue
Space occupying lesions (tumors)
Pulmonary edema
Lung resection
Radiation therapy (fibrotic changes)
Chemotherapy

17. Diffusing Capacity DLcosb Decreased in: Significance and Pathology
Emphysema
Chronic Bronchitis , Asthma (may or may not be decreased)
DLco sometimes used to differentiate between emphysema and chronic bronchitis

18. Diffusing Capacity DLcosb Significance and Pathology
In patients with COPD, DLco less than 50% of predicted is accompanied by O2 desaturation during exercise
Low resting DLco (<50% - 60% of predicted) may indicate the need for assessment of oxygenation during exercise

19. Diffusing Capacity DLcosb DL/VA
DLco is directly related to lung volume in healthy individuals
DL/VA is approximately 4-5 ml CO transferred/minute/liter of lung volume

20. Diffusing Capacity DLcosb DL/VA
DL/VA is useful in differentiating between restrictive and obstructive disease
Obstruction = Low DL/VA ratio
Restriction = DL/VA Ratio is preserved

21. Diffusing Capacity DLcosb DLco is affected by: Hemoglobin (Hb)
Corrections for Hb concentrations should be applied
Low Hb reduces DLco
High Hb elevates DLco
Carboxyhemoglobin (COHb)
Corrections for COHb should be applied
High COHb reduces DLco

22. Diffusing Capacity DLcosb DLco is affected by: Alveolar PCO2
Increased PCO2 elevates DLco
Hypoventilation
Pulmonary capillary blood volume
Increased blood volume causes increased DLco
Mueller maneuver
Increased cardiac output
Decrease pulmonary capillary blood volume causes decreased DLco
Valsalva maneuver

23. Diffusing Capacity DLcosb DLco is affected by:
Altitude above sea level
High altitude increases DLco
Poor inspiratory effort during testing
If less than 85% of VC will decrease DLco