DLCO carbon monoxide diffusing capacity

1. DLCOcarbon monoxide diffusing capacity Reporter: Ri ??? 91-6-17

2. Basic Concept DLgas may be affected by: Vgas (ml/min) PAgas-Pcgas (mmHg) ?DLgas = Vgas(STPD)/(PAgas-Pcgas) Choice of gas: may diffuse along the A-c pathway could be transported by hemoglobin ?O2 and CO

3. Basic Concept Why do we choose CO? 1.PcO2 value are not constant 2.High affinity to hemoglobin (210 times) ? PcCO =0 mmHg DLCO = Vco(STPD)/PACO

4. Basic Concept

5. Affecting Factor For DLCO A-c surface area Thickness of the alveolocapillary membrane Reaction rate of CO with hemoglobin Pulmonary capillary blood volume Lung volume V/Q mismatch Altitude Body position

6. DLCO Method Single-breath method (DLCO - SB) Steady-state method (DLCO - SS) Rebreathing method (DLCO - RB)

7. DLCO - SB

8. Breathing maneuver 1.exhale down to the RV level 2.single, rapid inspiratory VC maneuver and hold in the breath for a period of time (THold) 3.exhale rapidly back down to the RV level

9. Alveolar gas sampling is performed after the first approximately 1000ml are exhaled. Gas mixture: 0.3% CO, 10% He, room air

11. Calculation FACOI = FICO * (FEHe/FIHe) VA (STPD) = VVC (STPD) * (FIHe/FEHe) ?VVC (STPD) = VVC (ATPS) * STPD factor (Patm-PH2O) 273 = VVC (ATPS) * [--------------- * -----------] 760 (273+T)

12. Calculation FACOF = FACOI * e (KTHold) K= DLCO * (Patm-PH2O) / (VA * 60) DLCO – SB = VA (STPD) * 60 FACOI ------------------------ * Ln --------- (Patm-PH2O)(THold) FACOF

13. Hb correction Hb correction factor = 1 / (0.07 * gm Hb) Adjusted DLCO = measured DLCO * Hb correction factor

14. Advantages No invasive measuring procedures Analysis of only two gases is required Test is easily and rapidly performed

15. Disadvantages Difficult breathing maneuver Not practical during exercise testing Less than maximal inspired VC volumes affect measurement accuracy V/Q mismatches can affect the results

16. DLCO - SS

17. Breathing maneuver: normal tidal breathing Method: During the last two minutes of breathing (Tcol) Exhaled air is collected in a Douglas bag A sample volume (Vsam) is taken from this bag FECO, FECO2, FEN2 Gas mixture: 0.1% CO, balance air

18. Calculation DLCO – SS = VCO (STPD) / PACO VCO (STPD) VE (ATPS) = (Vcol + Vsam) / Tcol VE (STPD) = VE (ATPS) * STPD factor VCO (STPD) = VE (STPD) * (FACO – FECO) FACO = FICO * (FEN2 / FIN2) FIN2 = 1- (FIO2 + FICO2) FEN2 = 1- (FEO2 + FECO2)

19. PACO detection method PACO is more difficult because sample is contaminated with gas from the subject’s physiologic deadspace volume (VD) Deadspace – compensated techniques Estimated – deadspace technique Assumed – deadspace technique Alveolar gas sampling technique

20. Estimated – deadspace technique FACO2 = PaCO2 / (Patm – PH2O) VD FACO2 – FECO2 FACO – FECO ----- = ---------------------- = --------------------VT FACO2 FACO – FICO

21. Estimated – deadspace technique FACO2 FACO = (FICO - ----------) * (FICO-FECO) FECO2 PACO = (Patm - PH2O) * FACO

22. Assumed – deadspace technique (VT * FECO) – (VD * FICO) FACO = ----------------------------------- VT – VD PACO = (P Atm – P H2O) * FACO

23. Alveolar gas sampling technique Direct sampling of the subject’s end-tidal exhaled air during the last two minutes of the steady-state procedure ? PetCO PetCO = PACO (assume) Contraindication Small or uneven tidal breathing volumes During exercise

24. DLCO - SS Advantages Natural breathing maneuver Allow greater variety of clinical conditions Disadvantages More complex and difficult to perform (PACO) PCCO back pressure More affected by V/Q abnormalities

25. Deadspace – compensated technique Advantage Avoids errors that can occur with end-tidal PACO measurement Disadvantage Misestimation of VD can result in inaccurate PACO

26. Estimated – deadspace technique Advantage More accurate value for VD Disadvantage Requires an ABG sample

27. Assumed – deadspace technique Advantage Avoid ABG sampling Disadvantage Greater risk of VD misestimation

28. Alveolar gas sampling technique Advantage Avoids errors associated with VD misestimation Disadvantage Possible error in assuming that PetCO is equivalent to the mean PACO value

29. DLCO - RB

30. Breathing maneuver Exhales down to the RV level Keep 30 tidal breaths / min as possible The reservoir must be emptied completely with each inspiration Gas mixture: 0.3% CO, 10% He, balanced air Volume: equal to the subject’s FEV1

31. Rebreathing method techniques Reservoir – sampling technique Washout – sampling technique

32. Advantages Least affected by V / Q abnormalities Changes in the subject’s lung volume at the time of measurement

33. Disadvantages Complexity of the instrumentation and equations required Affected by PCCO buildup Need for subject cooperation with breathing PCCO back pressure

34. Overview of the DLCO method

35. Single – breath methods Simplest of all methods Perform a potentially difficult breathing maneuver Moderately affected by V /Q abnormalities Change in lung volume at the time of measurement can significantly affect test results

36. Steady – state methods Natural subject breathing Procedures are moderately complex Most likely to be affected by V / Q abnormalities

37. Rebreathing methods Least affected by V / Q abnormalities Most complex of all the methods

38. Conditions that produce changes in DLCO

39. Increased DLCO Left-to-right cardiovascular shunt Living at high altitude Exercise Left heart failure Supine position Early polycythemia

40. Decreased DLCO Emphysema Pulmonary resection Chronic hypersensitivity pneumonitis Lymphangitic spread of carcinoma Hamman-Rich disease (chronic interstitial pneumonitis) Histiocytosis

41. Decreased DLCO Oxygen toxicity Radiation-induced fibrosis Sarcoidosis Scleroderma lung disease SLE Pulmonary alveolar proteinosis Anemia

42. Decreased DLCO Pulmonary emboli Early collagen-vascular disorders Early miliary TB Early sarcoidosis

43. Severity for diffusion disorders

44. Thanks for your attention