1. Some Basics of Pulmonary Physiology
Douglas Wangensteen, Ph.D

2. The function of the lungs is to change venous blood into arterial blood, keeping PO2 and PCO2 relatively constant.

3. Where We’re Going Introduction Gas Exchange Mechanics of Breathing
- Diffusion
- Ventilation
- Causes of arterial hypoxemia
Mechanics of Breathing
- Airways resistance
- Elastic recoil
- Pulmonary function tests

4. Lung Anatomy Overview

5. How the Lungs Work

6. Where We’re Going Introduction Gas Exchange Mechanics of Breathing
- Diffusion
- Ventilation
- Causes of arterial hypoxemia
Mechanics of Breathing
- Airways resistance
- Elastic recoil
- Pulmonary function tests

7. About Diffusion

8. Diffusion is Efficient in Healthy Lungs

9. Measuring Alveolar - Capillary Diffusion: the Diffusion Capacity

10. Marie Krogh (~1910): Measure DLCO, not DLO2

11. About Ventilation

12. PACO2 Depends on VA and Metabolism

13. VA Determines PO2 and PCO2

14. Causes of Arterial Hypoxemia in Lung Injury and Disease
Hypoventilation
Slow diffusion between blood and alveolar gas
VA/Q mismatching
(Q = blood flow)
True shunts

15. For gas exchange to be efficient, ventilation and blood flow should be “matched” throughout the lungs.

16. When ventilation and blood flow are “mismatched” arterial PO2 will always be lower than normal.

17. A True Shunt is a Big Problem
Arterial PO2 is always reduced; breathing O2 won’t help much.

18. Important Points about Gas Exchange
VA should be at a level to provide normal arterial PO2 and PCO2.
Slow diffusion is generally not a problem.
Gas exchange is most efficient if VA and Q are matched within the lungs. If not, arterial PO2 will be reduced.

19. Where We’re Going Introduction Gas Exchange Mechanics of Breathing
- Diffusion
- Ventilation
- Causes of arterial hypoxemia
Mechanics of Breathing
- Airways resistance
- Elastic recoil
- Pulmonary function tests

20. How We Breathe at Rest

21. Lung-Thorax System

22. Overview

23. Airways Resistance

24. The Importance of Airway Radius

25. Lung Elastic Recoil
Compliance:
CL = DV/DPtp
~ ml/cm H2O

26. What determines lung elastic recoil?
Tissue Forces and Surface Tension Forces

27. Surface Tension Forces
The alveolar surface is covered with a thin aqueous layer.
Alveoli are small (r = 10-2 cm); if the interface was pure air:water
(g = 70 dyne cm-1) inflation would take 10x the pressure actually needed.
The lungs produce “Alveolar Surfactant” to reduce surface tension on the alveolar surface, so inflation requires less effort.

28. Alveolar Surfactant
DPPC

29. Production, Recycling by Type II Cells

30. Importance of Alveolar Surfactant:
Reduces surface tension on the alveolar surface, therefore reduces lung elastic recoil
Promotes alveolar stability because surface tension changes with alveolar area
When lung disease reduces or inactivates alveolar surfactant, breathing is more difficult and alveoli collapse.

31. Pulmonary Function Tests
A disease that increases airways resistance is called an OBSTRUCTIVE disease.
A disease that increases lung elastic recoil is called a RESTRICTIVE disease.
Both types of disease can have similar symptoms, so how can a diagnosis be made?
Measure lung volumes and maximum expiratory flow.

32. Lung Volumes

33. The Body Plethysmograph

34. Forced Vital Capacity Examples

35. Obstructive Disease Example

36. Restrictive Disease Example

37. Questions?

38. Because of alveolar surfactant, alveolar surface tension changes with area.

39. If alveolar surface tension was the same in every alveolus, gas would flow from small alveoli into large alveoli.
Small alveoli would collapse.