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DLCO
- 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
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- 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