Spirometry and Flow-Volume Curves - the Idiot’s Guide

1. Spirometry andFlow-Volume Curves- the Idiot’s Guide Dr Rod Taylor Consultant Respiratory Physician (part-time)

2. Bob Dylan at 70 Born on the 24th May 1941

3. History of Spirometry • 1846John Hutchinson • Defined Vital Capacity • Invented the Spirometer • 1947 Tiffeneau: FEV1 • VEMS: Vol. Expired Maximale, une Seconde • 1959 Wright: Peak Flow Meter

4. Dr. John Hutchinson 1811 – 1861 Findings are still valid today

5. Spirometry: The Big Paper

6. Hutchinson’s Spirometer From his 1846 paper

7. The Vital Capacity • Hutchinson 1846: “The greatest voluntary expiration, following the deepest inspiration” • Simple modern definition: “The biggest breath out, after the biggest breath in”

8. Studied 2,000 Subjects

9. Why no Women? “We do not know the vital capacity of women, nor is it easy to determine it, because of their tight dress.” Hutchinson 1852

10. We may never know… “We never heard a woman acknowledge that she wore her clothes tight.”

11. Brompton Hospital 1852 “Waste of time trying to do spirometry in women and girls: they are simply incapable of doing it.” Of course I can’t blow into it – I’m a woman! I’m pretty useless, too!

12. Spirometry Definitions • ForcedExpiratoryVolume in1second = FEV1 • The volume of air • expelled in the first second • of a maximal forced expiration • starting from full inspiration • i.e. the first 1 second of a FVC

13. 20% either side of Mean 80 – 120% of the mean predicted value For FVC ~ 1 litre either side of mean

14. Forced Expiratory Ratio 70% 100% FEV1 70% FVC Can blow out 70% of FVC in the first second

15. Predicted Values FEV1 and FVC vary with • Age • Gender • Height • Ethnic origin •  predicted value

16. Presenting Results (1) • Absolute values • e.g. FEV1/FVC = 3.75/4.60 litres • should always be given • Percentage of predicted value • e.g. FEV1 = 67% predicted • Forced expiratory ratio • e.g. FEV1/FVC = 53%

17. Presenting Results (2) Graphically • As volume-time curve: spirogram • As flow-volume curve • Examples will be shown

18. Classifying the Results (Remember, VC = biggest breath out after biggest breath in) So, only TWOcauses of a reduced VC! • Can’t get the air in =RESTRICTIVE • Can’t get the air out =OBSTRUCTIVE

19. Restrictive defect • The lungs are small • FVC is small • so FEV1 is also reduced • But no obstruction to expiration • so forced expiratory ratio (FEV1/FVC) • is normal – or even increased • becauseelastic recoil increased

20. Restrictive Defect The lungs are SMALL • Stiff and hard to expand • pulmonary fibrosis • Chest wall is rigid • ankylosing spondylitis • Respiratory muscles are weak • Guillain-Barré syndrome

21. Obstructive Defect Definition • FEV1 significantly reduced • to < 80% of predicted value • Forced expiratory ratio 70% or less • FEV1/FVC < 70% NB: Severe airflow obstruction reduces FVC as well as FEV1 , and so increases FER

22. Forced Expiratory RatioFEV1/FVC • Depends on both FEV1and FVC • Is reduced if • FEV1 is reduced • But goes back up again • if FVC is reduced • by incomplete expiration • or by severe airflow obstruction

23. Volume-Time Curve 6 5 4 FEV1 = 2.9 FVC = 5.6 Volume (litres) 3 FVC 2 FEV1 1 0 1 2 3 4 5 6 7 8 9 10 Time (seconds)

24. Carrot & Coriander Soup

25. The Flow-Volume Curve r h Volume = πr2h Flow

26. The Flow • Flow can be • derived from vol-time curve • measured directly

27. Deriving Flow A tangent to the curve gives the flow at that point Flow = volume/time Volume Time

28. Deriving Flow Zero at start (TLC) Flow very fast at first Slows soon after this Gets steadily slower Zero when reach RV Volume Time

29. Measuring Flow Directly Beaufort Scale 1805 Rear Admiral Sir Francis Beaufort 1777-1857

30. Forever blowing bubbles?

31. Personal Airflow Meter Portable Readily available Cheap Easy to use Non-invasive No batteries needed Duplicated

32. No Time At All! There is no time-scale on a flow-volume curve. But some spirometers do have an in-built timer to mark the FEV1.

33. Flow-Volume CurveThe Volume (1)

34. Flow-Volume CurveThe Volume (2)

35. Flow - the Basic Shape At TLC, flow = zero by definition At RV, flow = zero by definition Flow reaches a peak soon after start of expiration, then slows steadily

36. Expiratory FlowAt TLC: before start to blow Expiratory Flow Expiratory flow = Zero Expired Volume

37. Expiratory FlowSoon after start blowing Peak Flow

38. Expiratory FlowAs expiration progresses Flow slows progressively

39. Expiratory FlowAt Residual Volume

40. Expiratory F-V Curve Peak Flow

41. Mild airflow obstruction Slightly concave throughout expiration Airflow is reduced at a given lung volume, because the airway is narrower. Sometimes called ‘volume dependent’ reduction in flow.

42. Bronchodilator Effect Peak flow Before Flow has increased throughout expiration, and peak flow slightly. In this example, there is no increase in FVC. After

43. Compliance – Stretchiness! High compliance: easy to stretch, not much recoil

44. Medium Compliance Harder to stretch Stronger recoil

45. Low Compliance Much harder to stretch Much stronger recoil

46. How the Lung Behaves I am really elastic! Stretch me and I spring back!

47. Airway, Lung and Pleura Airway Negative pressure ‘physiological glue’ Parietal pleura Elastic lung tissue Visceral pleura Negative pressure ‘glue’

48. Compliance – Stretchiness! ‘Glued’ to airway wall ‘Glued’ to chest wall Elastic lung tissue

49. Airway Guy-Lines Chest wall Airway

50. Held open by Guy-lines Airflow Airway held open The natural elasticity of the normal lung tissue pulls the airway open