Assessment of respiratory system function

1. Assessment of respiratory system function Stanislav Matoušek

2. What is the function of lungs? Alveolus • Ventilation – mechanical function of the lung – get air in and out • Perfusion with blood – get blood in and out • Diffusion – get gas molecules from air to blood and back • Matching of ventilation and perfusion

3. Possible respiratory system disturbances • // ventilation • // perfusion • // distribution of ventilation and per-fusion = ventilation perfusion mismatch • // diffusion • Important: Ventilation, perfusion and their distribution are feedback regulated processes. • Disturbance: • 1. In the effector part (lungs, resp. muscles for ventilation, heart for perfusion) • 2. In the regulator part (sensors, CNS eg. in uremia, liver in hepatopulmonary syndrome)

4. The overallmeasureof respiratory system function • pO2&pCO2 in arterial blood - („Astrup“) • O2 solubility in water is low => need of Hemoglobin • pO2 = 13,3 kPa = 100 Torr • pCO2 = 5,3 kPa = 40 Torr (1 kPa = 10 cm H2O = 7,6 mmHg or Torr)

5. Solubility of gases in liquids

6. Oxygen-hemoglobin dissociation curve

7. Ventilation • Is carried out by respiratory muscles, that change volume of thorax. • Volume changes cause changes of pressures • Changes of pressure in alveoli cause air flow ( • ↑ transthoracic pressure – expiration; • ↓ transthoracic ressure – inspiration) • Flow behaves according to Ohm’s law

8. Spirometry - Measure of ventilation volumes (and air flow)

9. Spirometry

10. Spirometry – Volume-flow loop

11. -12 mmHg +1 mmHg Pressures in the lungs Transpulmo-nary pressure Transthoracic pressure

12. Normal lung

13. Lung compliance • Is a measure of the pressures developed by the effect of the lung elasticity while the lung is at rest. • C= Vbreath/(pendin.- pendexp.) =ΔV /Δ p • The pressures are not pressures needed to make the air flow (it is measured at rest/0 flow points • They are pressures needed to keep the lung inflated !! • The more you want to have the lung inflated, the more pressure you need • Decreased compliance = stiff lung = restrictive disease • Increased compliance - loose lung – emphysema – (increased compliance does not cause problems by itself.However, it causes increased resistance during expiration)

14. Restrictive disease

15. Depends on pressures needed to make the air flow (transthoracic in normal breathing) R= (penviron.- palv.)/ F=Δ p / F Increased resistance – obstruction in the lungs – obstructive desease Lung resistence

16. Obstructive disease

17. Measuring of the Compliance of the lungs • C= Vbreath / (pendin.- pendexp.) • Direct – difficult, because you need to measure the transpulmonary pressure difference • Easy in artificial ventilation • Indirect - decreased lung compliance = stiff lung - will cause ↓ decreased static lung volumes, especially ↓in VC a FVC.

18. Measuring of the resistance of the airways R= (penviron.- palv.)/ F Direct: Temporary occlusion method (spirometry, whole body pletysmography) Indirect:Increased airway resistance = blonchoconstriction will cause decrease of flow and „dynamic lung volumes“ FEV1, FEF25-75% and MEFs. -12 mmHg +1 mmHg

19. What type of lung disease? a) b) c)

20. Normal spirogram

21. Obstruction- medium degree

22. Obstruction parameters

23. Restrictive disease

25. Real world situation

26. Whole body plethysmography

27. Other methods of measuring Residual volume and TLC • Nitrogen washout method -person breathes in pure oxygen - concentration of N2 in the expired air is measured • Helium dilution method • Given amount of Helium

28. Ventilation disorders • Lung impairment (mechanical properties change) • Obstructive disease - ↑ increased resistance R of airways (R = “dynamic lung resistance”) • Restrictivedisease– ↓decreasedlung compliance C (‘↑ static resistance” `;C = 1/ static lung resistance) • Chest wall impairment • ↓ decreased C of chest wall – severe scoliosis, extensive fibrosis, serial fractures • Insufficient activity of respiratory muscles (// innervation or // muscle strength , // of CNS )– E.g.. Respiratory centre suppression in barbiturate poisoning, myasthenia gravis

29. Perfusion • All the blood volume flows through lungs • Also behaves according to Ohm’s law

30. Disorders of perfusion • Causes • Embolization to the pulmonary artery (increased resistante to the blood flow) • Pulmonary hypotension (right heart failure) • Pulmonary hypertension • Manifestation • Pulmonary hypertension causing ever right heart failure in massive embolism • Decrease in pO2 (increase in pCO2), • Increase of shunting • Blood flows fast through a small part of the lungs only – the rest functions as dead space

31. Measuring perfusion • a) Ventilation - perfusion scan - diagnosis of pulmonary embolism and parenchymal lung diseaseshould be performed in all clinically stable patients with the suspicion of pulmonary embolism should be performed in all clinically stable patients with the suspicion of pulmonary embolism - Ventilation scan - 133Xe gas- Perfusion scan – microspheres of albumin (50-100 mm labeled with gamma emitting isotope 99mTc- “Mismatch” in ventilation and perfusion ischaracteristic for PTE

32. Lung scintigraphy -perfusion

33. Lung scintigraphy - ventilation

34. West’sweir

35. Physiological ventilation distribution

36. Distribution of ventilation and perfusion • In healthy lung, the most perfused part is at the base…this part is at the same time the most ventilated one (No mismatch ) • Various pathologies can cause ventilation perfusion mismatch • Every lung region (size is on us to decide) has its ventilation perfusion ratioVA/Q - numberfrom O to ∞ … norm0,8 - 1

37. Pulmonary shunt • Extreme case of ventilation perfusion mismatch • Zero local ventilationVA/Q = O Causes: • Atelectasis • Lung edema (alveolar) • Lunginflammation (inflammatory exsudate) • Collapsed lung(pneumothorax) • Blood leaving the defect area haslow ↓pO2andhigh ↑ pCO2 (no gas exchange) • After mixingwith blood from healthy regions,↓pO2 stays low, butpCO2 normalizes. Why?

38. Dead space • Opposite extreme case of ventilation-perfusion mismatch. No perfusion. • VA/Q = ∞ • Increases of dead space: • Embolism • Emphysema • Bronchiectasia • Ventilation of dead space has by itself no influence on blood gases, but it is wasted respiratory work! => • Excessive ventilation of dead space can lead to insufficient ventilation of healthy alveoli.

39. Physiological dead space

40. Ventilation perfusion mismatch

41. Ventilation perfusion mismatch • Is a very common cause of hypoxemia - ↓ pO2 (low ↑ pCO2 might probably not occur) • Etiological factor of dyspnea onset in: • ARDS • COPD, especiallychronic bronchitis (smoker) • Asthma

42. Diffusion

43. Diffusion in lungs

44. Rate of diffusion

45. Diffusion impairments Decrease ↓ of diffusion surface S: • Emphysema • Pneumothorax Increase ↑ in diffusion distance d: • Lung fibrosis • Lung edema • Interstitial pneumonia

46. Measuring „diffusion“ • Transfer factor / Lung diffusion capacity

47. Respiratory insufficiency!! • Respiratory insufficiency type I (partial, hypoxemic) • pO2 is ↓ low, but pCO2 is normal oreven also ↓lower • Respiratory insufficiency type II (global, hypoventilation) • pO2 is ↓ lowandpCO2 is ↑ high (respiratory a….)

48. Partial respiratory insufficiency(Type I) • Impaired // distribution • Ventilation perfusion mismatch - uneven VA/Q in different lung regions • True shunting (right-left) • Impaired // diffusion • Through water O2 diffuses about 20x slower than CO2

49. Global respiratory insufficiency(type II) • Impaired // ventilation -overall alveolar hypoventilation

50. ARDS • Adult/acute respiratory distress syndrom • Cause: Sudden damage to alveolo-capillary membrane – interstice and alveoli get infiltrated byplasmaand proteins • Ventilation-perfusion mismatch appears, in some parts of lungsto the degree of shunting • Consequence:Partial respiratory insufficiency in serious cases evolving into global respiratory insufficiency • With edema, lung compliance decreases ↓C, where only interstitial edema => // diffusion