1. Australian & New Zealand Society of Respiratory Science Danny Brazzale, CRFS Senior Respiratory Scientist Austin Hospital, Institute for Breathing and Sleep, Melbourne, VIC Nuts and Bolts of T L CO CRFS Physiology Review Workshop, Perth 2016

2. ANZSRS, Perth 2016 Click to edit Master title style Click to edit Master text styles Second level Third level Fourth level Fifth level My Disclosure The following presentation will NOT include discussion on any commercial products or service and that there are NO financial interests or relationships with any of the Commercial Supporters of this years ASM

3. ANZSRS, Perth 2016 Click to edit Master title style Click to edit Master text styles Second level Third level Fourth level Fifth level Outline Background Measurement technique Calculations Equipment QC Standardisation issues –Breath-hold time –Washout and sample collection Factors affecting T L CO measurement –Submaximal inspiration Alveolar volume as a measure of TLC

4. ANZSRS, Perth 2016 Click to edit Master title style Click to edit Master text styles Second level Third level Fourth level Fifth level T L CO Test used to assess the ability of the lungs to transfer gases from the alveoli to the blood. First developed in 1914 by M Krogh. Several methods available (re-breathing, intra-breath) Single breath technique is the most common. Forster and Roughton (1957) along with Ogilvie (1957) further developed the technique. CO is used rather than oxygen because –Partial pressure of oxygen in the blood is not zero

5. ANZSRS, Perth 2016 Click to edit Master title style Click to edit Master text styles Second level Third level Fourth level Fifth level T L CO Alveolar-capillary membrane. Red blood cell Plasma Quantifies –Integrity of alveolar-capillary membrane –Integrity of pulmonary vasculature CO

6. ANZSRS, Perth 2016 Click to edit Master title style Click to edit Master text styles Second level Third level Fourth level Fifth level T L CO The units tell us about what we are measuring. ml(STPD)/min/mmHg (or SI units mmol/min/kPa) –Rate of uptake (ml/min) –Divided by driving pressure (mmHg) CO uptake can be split into –Membrane conductivity (Dm) –Binding of CO and Hb »Can be represented as product of COHb reaction rate and volume of Hb in alveolar capillary blood (  Vc) 1 1 + 1 T L CO = Dm  Vc

7. ANZSRS, Perth 2016 Click to edit Master title style Click to edit Master text styles Second level Third level Fourth level Fifth level Single Breath T L CO

8. ANZSRS, Perth 2016 Click to edit Master title style Click to edit Master text styles Second level Third level Fourth level Fifth level Measurement technique Patient exhales to RV Inhales test gas (0.3% CO plus tracer/inert gas) to TLC Breath holds for about 8 secs Exhales again to allow alveolar sample to be collected

9. ANZSRS, Perth 2016 Click to edit Master title style Click to edit Master text styles Second level Third level Fourth level Fifth level Gas concentrations during T L CO

10. ANZSRS, Perth 2016 Click to edit Master title style Click to edit Master text styles Second level Third level Fourth level Fifth level Test gas CO concentration should be 0.3%, however since ratios are more important, exact concentrations not critical. Tracer gas is used to determine initial alveolar concentration of CO, however it also enable us to measure V A Tracer gas needs to be relatively insoluble, inert and have diffusivity similar to CO – helium (He), methane (CH 4 ). Balance of gas is air leaving FiO 2 of 0.17 - 0.21 depending on amount of tracer gas –This is important because O 2 competes with CO for binding sites.

11. ANZSRS, Perth 2016 Click to edit Master title style Click to edit Master text styles Second level Third level Fourth level Fifth level Tracer gas – alveolar volume V A = (V I - V D ) X (F I TR/F A TR) F I TR = inhaled fraction of the inert tracer gas. V I = volume of the inspired tracer gas. F A TR = alveolar fraction of the tracer gas. V A = alveolar volume (quoted at BTPS). V D = deadspace (anatomic + instrument) Most importantly the (F I TR/F A TR) value is used to calculate the initial alveolar concentration of CO

12. ANZSRS, Perth 2016 Click to edit Master title style Click to edit Master text styles Second level Third level Fourth level Fifth level TLCO measurement Transfer factor defined as the rate of gas uptake divided by the driving pressure (units are ml/min/mmHg) T L CO = VCO P A CO Where VCO is the rate of carbon monoxide uptake and P A CO alveolar partial pressure of CO. T L CO = V A x 60 x Ln(F A TRxF I CO) (P B – P H20 ) x BHT (F I TRxF A CO) where P B is barometric pressure, BHT is breath hold time, F I CO is the inspired fraction of CO, F A CO is expired fraction of CO, F I TR is the inspired fraction of the tracer gas and F A TR is expired fraction of the tracer gas, V A at STPD.

13. ANZSRS, Perth 2016 Click to edit Master title style Click to edit Master text styles Second level Third level Fourth level Fifth level Equipment QC (ERS/ATS 2005) Gas analyser zero (before/after each test) –Checking for drift (largely automated) Volume accuracy (daily) –3L syringe Control subject or simulator (weekly ) –>10% change in control may indicate a problem Gas analyser linearity (3 monthly) –At least one intermediate measure »Purchase special gas mix (eg 0.15%CO, 7% He, Bal air) »Serial dilution using a syringe Timer (3 monthly) – not easy on computerised systems

14. ANZSRS, Perth 2016 Click to edit Master title style Click to edit Master text styles Second level Third level Fourth level Fifth level Gas analyser considerations Gas analyser accuracy T L CO = V A x 60 Ln(F A TRxF I CO) (P B – P H20 ) x BHT (F I TRxF A CO) –Accuracy as such not important however linearity is important (0.5% of full scale) –0.3/0.15 (2) is the same as 0.2/0.1(2) –Minimal gas analyser drift (setting zero) is very important –0.3/0.15 (2) not the same as 0.2/0.05 (4)

15. ANZSRS, Perth 2016 Click to edit Master title style Click to edit Master text styles Second level Third level Fourth level Fifth level Analyser linearity At least one intermediate measure Can be difficult to do on computerised systems –Special gas mix (eg 0.15%CO, 7% He, Bal air) –Serial dilution using a syringe »What should the T L CO of a syringe be? »Plot expired/inspired ratio of CO vs tracer gas

16. ANZSRS, Perth 2016 Click to edit Master title style Click to edit Master text styles Second level Third level Fourth level Fifth level Standardisation issues (ERS/ATS 2005) Inspiratory manoeuvre –Should be rapid (<4secs) as the calculation assumes instantaneous filling –Should be at least 85% of best VC. Breath-hold and expiration –Relaxed breath-hold (no Valsalva and Muller manoeuvres) –Valsalva manoeuvre (pushing against a closed airway) will decrease thoracic blood volume and hence decrease T L CO –Breath-hold should be 10±2 secs –Smooth exhalation with <3 secs sample collection time and <4secs total (washout + sample).

17. ANZSRS, Perth 2016 Click to edit Master title style Click to edit Master text styles Second level Third level Fourth level Fifth level Breath-hold time (Ogilvie) Beginning of inspiration to beginning of sample volume –Define beginning of inspiration using back extrapolation (like spirometry) washout sample

18. ANZSRS, Perth 2016 Click to edit Master title style Click to edit Master text styles Second level Third level Fourth level Fifth level Breath-hold time (ESP) 50% of inspired volume to beginning of sample volume –Define beginning of inspiration using back extrapolation (like spirometry) washout sample

19. ANZSRS, Perth 2016 Click to edit Master title style Click to edit Master text styles Second level Third level Fourth level Fifth level Breath-hold time (Jones-Meade) From 0.3 of inspired time to half of sample time –Define beginning of inspiration using back extrapolation (like spirometry) washout sample

20. ANZSRS, Perth 2016 Click to edit Master title style Click to edit Master text styles Second level Third level Fourth level Fifth level Breath-hold time effects Using above example –ESP breath-hold shorter than Ogilvie and Jones-Meade   T L CO –Jones-Meade and Ogilvie BHT very similar Differences magnified with slower inspiration and expiration Jones-Meade recommended by ATS/ERS 2005 guidelines –Takes into account that inspiration and expiration not instantaneous Ogilvie ESP Jones-Meade

21. ANZSRS, Perth 2016 Click to edit Master title style Click to edit Master text styles Second level Third level Fourth level Fifth level Standardisation issues (ERS/ATS 2005) Washout and sample collection –Need to clear dead-space to get alveolar sample –Washout should be 0.75-1.0 L (0.5L of VC < 2L) –If continuous analysers are used need to make sure dead- space is clear and adequate alveolar sample is collected –Sample volume should be 0.5-1.0L (maybe < 0.5L if VC < 1L)

22. ANZSRS, Perth 2016 Click to edit Master title style Click to edit Master text styles Second level Third level Fourth level Fifth level Inadequate clearance of deadspace  Inert gas value  V A  CO value  T L CO (despite  BHT) Sample includes gas from non gas- exchanging area Values closer to test gas

23. ANZSRS, Perth 2016 Click to edit Master title style Click to edit Master text styles Second level Third level Fourth level Fifth level Standardisation issues (ERS/ATS 2005) Other factors –Interval between tests >4 mins –13% change during menstrual cycle (at least in part due to Hb) –Alcohol may decrease T L CO (or interfere with gas analysers) –Breath hold time calculation –Dead-space for calculation V A »Some have used fixed value of 150ml »2.2ml/kg body weight or »24 x ht(cm) x ht(cm)/4545 if BMI>30

24. ANZSRS, Perth 2016 Click to edit Master title style Click to edit Master text styles Second level Third level Fourth level Fifth level Evaluating the measurement of T L CO Acceptable test –Properly controlled equipment –V I >85% of largest (F)VC in < 4 secs –Stable breath-hold for 10±2 secs –Sample collection time of <3secs with appropriate clearance of V D and proper alveolar sample Repeatability –2 acceptable tests within 3 units or 10% of the highest value. –The average of these measurements should be reported

25. ANZSRS, Perth 2016 Click to edit Master title style Click to edit Master text styles Second level Third level Fourth level Fifth level Factors altering T L CO Reduced T L CO erect posture valsalva manoeuvre hyperoxia anaemia lesser inhalation Increased T L CO supine position Muller manoeuvre hypoxia polycythaemia larger inhalation exercise

26. ANZSRS, Perth 2016 Click to edit Master title style Click to edit Master text styles Second level Third level Fourth level Fifth level Factors affecting T L CO measurement Haemoglobin -  Hb  reduction in T L CO. T L CO reported as corrected for Hb to 14.6 g/dL for males and 13.4 g/dL for females and children<15 years to standardise results. Elevated COHb –  in T L CO due to  diffusion gradient & anaemia-like effect caused by COHb back pressure. –Common causes - smoking & no of T L CO efforts –COHb  ~0.7% with each T L CO effort Alveolar pO2 -  T L CO with a reduction in P A O 2 – less competition for CO to bind to Hb. –T L CO  ~0.33% for each 1mmHg fall in P A O 2

27. ANZSRS, Perth 2016 Click to edit Master title style Click to edit Master text styles Second level Third level Fourth level Fifth level Factors affecting T L CO measurement V I <85% largest VC – May lead to reduction in calculated V A. As lung volumes are reduced fall in T L CO is much less than the fall in V A. Pulmonary capillary blood volume – less blood volume  less binding sites  lower T L CO Body position – supine causes  T L CO as pulmonary blood flow distribution changes.

28. ANZSRS, Perth 2016 Click to edit Master title style Click to edit Master text styles Second level Third level Fourth level Fifth level Effects of submaximal inspiration Submaximal inspiration from RV (test done below TLC) –V A reduced with T L CO less so Original test Test done below TLC KCO increases

29. ANZSRS, Perth 2016 Click to edit Master title style Click to edit Master text styles Second level Third level Fourth level Fifth level Effects of submaximal inspiration Submaximal inspiration from above RV (test done at TLC) –V A and T L CO should accurately reflect true values Test done at TLC Lower exp inert gas and CO More dilution Little change in T L CO &V A

30. ANZSRS, Perth 2016 Click to edit Master title style Click to edit Master text styles Second level Third level Fourth level Fifth level Effects of submaximal inspiration Trouble is its difficult to know which happened Easy to tell on the examples, but T L CO guidelines suggest deep inspirations prior to exhalation before delivering test gas should not be done as it increases the measured T L CO.

31. ANZSRS, Perth 2016 Click to edit Master title style Click to edit Master text styles Second level Third level Fourth level Fifth level Alveolar volume as a measure of TLC Alveolar volume - single breath estimate of TLC In a perfect world (and a perfect subject) V A = TLC – patient V D Can we use V A to estimate TLC? What determines how good this estimate would be? 1998 paper by Punjabi et al –2477 patients –V A measured using standard technique, however did not subtract anatomic deadspace –TLC measured using He dilution lung volumes »Data may be worse when compared to plethysmographic TLC

32. ANZSRS, Perth 2016 Click to edit Master title style Click to edit Master text styles Second level Third level Fourth level Fifth level What about using V A instead of TLC ? Although there is some scatter V A measurements correlate well in non-obstructed patients However there can be a large difference in obstructed patients N Punjabi, D Shade & R Wise. Correction of single-breath helium lung volumes in patients with airflow obstruction. Chest 1998; 114: 907- 918.

33. ANZSRS, Perth 2016 Click to edit Master title style Click to edit Master text styles Second level Third level Fourth level Fifth level Sample Question Available binding sites Components of T L CO

34. ANZSRS, Perth 2016 Click to edit Master title style Click to edit Master text styles Second level Third level Fourth level Fifth level Sample Question Process of elimination introduction

35. ANZSRS, Perth 2016 Click to edit Master title style Click to edit Master text styles Second level Third level Fourth level Fifth level Sample Question Think logically

36. ANZSRS, Perth 2016 Click to edit Master title style Click to edit Master text styles Second level Third level Fourth level Fifth level Controversies & Current Issues “The relationship between TLCO and lung volume is not linear, so TLCO/VA (KCO) does not provide an appropriate way to normalize TLCO for lung volume.” VA as a fraction of TLC TLCO or KCO fraction at TLC Respir Med 2000; 94:28 24 healthy subjects taking sub-maximal inhalations of TLCO test gas KCO DLCO

37. ANZSRS, Perth 2016 Click to edit Master title style Click to edit Master text styles Second level Third level Fourth level Fifth level Adjustments prior to interpretation. Lung volume –The relationship between T L CO and lung volume is complex and non-linear. –Reduction in T L CO is less than the reduction in V A. –Some equations available to correct T L CO for a reduced VA however no firm recommendation made.