LUNG VOLUMES AND DIFFUSION TESTS

1. LUNG VOLUMES AND DIFFUSION TESTS Prof. Dr. Deniz DOĞRU ERSÖZ Hacettepe University Faculty of Medicine Pediatric Pulmonary Medicine Unit

2. Lung volumes • Functional residual capacity (FRC): The volume of air in the lungs • at the end of atidal breath • Residual volume (RV): The volume of air in the lungs • at the end of a maximum expiration • Total akciğer kapasitesi (TLC): The volume of air in the lungs • at the end of a maximum inspiration

3. Indications of Lung Volume Measurements • To diagnose restrictive pulmonary disease and assess its severity • To discriminate obstructive and restrictive disease • To diagnose gas trapping • To monitor response to therapy (Bronkodilator, steroid, lung surgery, transplantation, radiation, chemotherapy) • Preoperative evaluation

4. Measurements of Lung Volumes • FRC is measured generally • TLC is measured by some methods • RV is measured indirectly

5. Measurements of Lung Volumes • Inert gas dilution: Lung volumes are measured with a known volume and concentration of a gas (Helium) • Nitrogen washout: Lung volumes are measured by expired nitrogen concentration before and after inspiring pure oxygen • Whole body pletismography: Lung volumes are measured by Boyle’s law, with changes in the pressure and volume while breathing in a closed box

6. Lung volume measurement techniques • Closed circuit, Helium dilution, “multiple breath” • Open circuit, multiple breath N2 washout • Single breath N2 washout • Single breath Helium dilution • Plethysmography • Radiologic methods

7. Akciğer Hacimlerinin Ölçüm Teknikleri • Closed circuit, Helium dilution, FRC “multiple breath” • Open circuit, FRC multiple breath N2 washout • Single breath N2 washout TLC • Single breath Helium dilution TLC • Plethysmography FRC • Radiologic methods TLC

8. Closed circuit, Helium dilution, “multiple breath” • The technique relies on inhalation of a known concentration and volume of helium mixture and its homogenous distribution to both lungs

9. Closed circuit, Helium dilution, “multiple breath” • Helium: preferred as it is not dissolved in blood and can be measured by inexpensive methods • A spirometry is filled with a mixture of helium and oxygen (25-30% oxygen, 10% He)

10. Closed circuit, Helium dilution, “multiple breath” • Patient is asked to breath quietly (tidal breath) through a sterile mouthpiece with nose clip attached for 30-60 seconds • At the end of a normal tidal breath a valve is opened and the patient commences breathing the helium mixture from the spirometer • Test ends when He is balanced • Test duration 7-10 minutes

11. Closed circuit, Helium dilution, “multiple breath” • The amount of helium remains constant throughout the test as the circuit is closed • The change in He concentration in the spirometer shows the lung volume of patient

12. Closed circuit, Helium dilution, “multiple breath”

13. Closed circuit, Helium dilution, “multiple breath” System volume (L) = He added F He initial (% He initial - %He final) FRC = x System volume %He final

14. Open circuit,multiple breath Nitrogen washout

15. Open circuit,multiple breath Nitrogen washout Alveolar nitrogen concentration Nitrogen concentration in the atmosphere 79% = = 79% of the patient’s FRC is nitrogen

16. Open circuit,multiple breath Nitrogen washout • Measurement of the nitrogen washed out while breathing 100% oxygen • Lung volumes are measured by comparing initial alveolar and exhaled nitrogen concentration • Test duration is generally 3 minutes

17. Open circuit,multiple breath Nitrogen washout • Patient breaths normally for 30-60 seconds • At the point of a normal end tidal breath the patient commences breathing 100% oxygen • Patient breaths normally for 3 minutes • In this duration, the nitrogen is washed out of the lungs • Expired nitrogen volume is monitorized • Test ends when consecutive 3 expired N2concentration is < 1.5%

18. Open circuit,multiple breath Nitrogen washout

19. Open circuit,multiple breath Nitrogen washout

20. Whole Body Plethysmography

21. Plethysmography • Thoracic gas volume (VTG) is measured • VTG: The gas contained in thorax whether in communication with patent airways or trapped in any compartment of the thorax • VTG: Measured at the end of expiration and equal to FRC • Patient sits in a closed box • The changes in box pressure occur in direct proportion to volume changes occuring in thorax

22. Plethysmography The test employs Boyle’s law The relationship between the pressure and volume of a gas at a given temperature remains constant (P1xV1 = P2xV2)

23. Plethysmography Because the relationship of gas/pressure within the lungs and gas/pressure within the box must remain constant, the increase in chest volume is associated with a corresponding change in box pressure

25. Plethysmography Technique • The patient sits inside the box and the door is closed • While the patient breaths normally, air temperature in the box is allowed to stabilize for 30 seconds • After a period of stabilization, the shutter is transiently closed at the end of a normal tidal expiration

26. Plethysmography Technique • The patient is asked to pant for several breaths (1-2 breath/second) • Cheeks are supported with hands • Patient should breath with shallow breaths with a constant volume

28. VTG Manuever

29. Panting manuever Properly performed panting manuever Series ofalmost superimposed straight lines separated by only a small thermal drift

31. Criteria for acceptability • The panting manuever should be at an appropriate volume and rate (1-2 breaths/second) • The loop should be closed and not drift accross the screen • The loop drifting across the screen shows that the thermal equilibrium has not been reached and panting volume is too high • Reported VTG is averaged from 3 to 5 acceptable panting manuevers

32. Advantages of Plethysmography Measurement of VTG with pletismography is • Easier • Shorter time • More accurate result when compared to dilution methods as it measures whole gas volume in thorax

33. Disadvantages of Plethysmography • A complex procedure • The manuevers should be instructed carefully in details • Can cause claustrophobia

34. Interpreting Lung Volumes Factors affecting FRC • Weight, length • Sex • Race • Ethnicity • Changes in body position • Diurnal variations

37. Increase in FRC • Increase is pathologic • > 120% means air trapping • Emphysema • Asthma • Bronchitis • Lung surgery (Lobectomy)

38. Increase in RV • Acute asthma attack • Chronic air trapping (Emphysema, obstruction of bronchi) • RV and FRC increase together, generally • As RV increases: More ventilation is done in order to obtain gas exchange VT, respiratory rate increase Work of breathing is increased Hypoxemia, carbondioxide retention

39. RV/TLC ratio • Describes the percentage of total lung volume that must be ventilated by tidal breathing • 20-35% in healthy adults • RV/TLC : RV veya TLC RV/TLC : TLC Hyperinflation TLC normal Air trapping

40. Obstructive Diseases • RV is always increased • VC is decreased, TLC remains normal (Air trapping) • VC is normal, TLC is increased (Hyperinflation)

41. Obstruction TLC TLC TLC FRC FRC FRC RV RV RV RV Normal Air trapping Hyperinflation

42. Obstructive Diseases • Asthma • Chronic bronchitis • Bronchiectasis • Cystic fibrosis • Emphysema TLC is normal or increased FRC is increased

43. Restrictive Diseases • FRC, RV, TLC are decreased • Volumes are generally equally reduced • RV/TLC normal

44. Restriction TLC TLC FRC FRC RV RV Normal Restriction

45. Restrictive Diseases • Interstitial lung diseases with fibrosis • Pneumonia • Masses in thorax • Chest wall diseases • Pleura diseases • Neuromuscular diseases • Obesity • Congestive heart failure

46. CARBON MONOXIDE DIFFUSING CAPACITY

47. DIFFUSING CAPACITY • Measures the transfer of oxygen from alveoli to hemoglobin across alveolocapillary membrane • Carbon monoxide is used (CO) • CO, follows the same diffusion way as oxygen asn easy to measure

48. DIFFUSING CAPACITY

49. DIFFUSING CAPACITY • DLCO • Assesses gas exchange of lungs (especially venous oxygenization) • Measures transport carbon monoxide from the alveolacapillary mambrane whose diffusion is limited

50. Technique • CO, combines with hemoglobin 210 times more readily than oxygen • In presence of normal amounts of Hb and normal ventilatory function, the primary limiting factor to diffusion of CO is the status of alveolocapillary membrane • There is normally little or no CO in pulmonary capillary blood • The pressure gradient causing diffusion is basically the alveolar pressure (PACO) • If the partial pressure of CO in the alveoli and the rate of uptake in gas can be measured, DLCO can be determined