1. Mechanics of Breathing
Chapter 17
Mechanics of Breathing

2. About this Chapter Structure and function of the respiratory pumps
How gases are exchanged with blood
The role of pressures and surfactants in rate of exchange
How respiration is regulated

3. Respiratory System: Overview
Lungs: exchange surface
75 m2
Thin walled
Moist
Ribs & skin protect
Diaphragm & ribs pump air

4. Interesting Facts about the Lungs
Each lung contains approximately 150 million alveoli
We lose half a liter of fluid a day from breathing
Normal breathing rate is between breaths per minute, but women and children breathe faster than men
Breathing rate may to increase to 60 after exercise
The capillaries in the lung would extend approximately 1000 miles if laid end to end
Approximately 1500 miles of airways are found in the lungs
A typical sneeze travels at a velocity of 100 miles per hour
The right lung is larger than the left lung and has three lobes as compared to 2 for the left
Every minute we breathe 13 pints of air or 6.15 Liters/min
We inhale and exhale approximately 22,000 times/day

5. Respiratory System: Overview
Figure 17-2 b: Anatomy Summary

6. Respiratory System Structure
Conduction zone: pathway for pulmonary ventilation
Respiratory zone: membrane for gas exchange  external respiration
Clinically, two parts:
Upper respiratory tract
Lower respiratory tract

7. Cross Section Through Lung

8. Smoker’s Lungs
Non-smoker 

10. Lung Tissue slide Respiratory Bronchiole Alveolar Duct Alveoli
Alveolar Sac

11. Functions of the Respiratory System: Overview
Exchange O2
Air to blood
Blood to cells
Exchange CO2
Cells to blood
Blood to air
Regulate blood pH
Vocalizations
Protect alveoli
Figure 17-1: Overview of external and cellular respiration

12. The Airways: Conduction of Air from Outside to Alveoli
Filter, warm & moisten air
Nose, (mouth), trachea, bronchi & bronchioles
Huge increase in cross sectional area
Figure 17-4: Branching of the airways

13. Key Gas Laws Reviewed Gas is compressible & flow  with  resistance
Air is a mix of gases, each diffuses independently

14. Key Gas Laws Reviewed Solubility of a gas depends on:
Partial pressure of that gas (example: O2 =156 mmHg)
Temperature
Solubility in a particular solvent
Water: solvent for life
O2 into water: 0.1 m moles/L (poor)
CO2 into water: 3.0 m mole/L (good)

15. Ventilation: The Pumps
Inspiration
Expiration
Diaphragm
Low energy pump
Concavity – flattens
Thorax: ribs & muscles
Pleura: double membrane
Vacuum seal
Fluid-lubrication

17. Ventilation: The Pumps
Figure a: Surfactant reduces surface tension

18. Respiratory Damage & Diseases
Pneumothorax ("collapsed lung")
Fibrotic Lung Disease
Emphysema
Chronic Bronchitis
Asthma
NRDS

20. Pink Puffer-Emphysema is Primary Problem
A "pink puffer" is a person where emphysema is the primary underlying pathology. As you recall, emphysema results from destruction of the airways distal to the terminal bronchiole--which also includes the gradual destruction of the pulmonary capillary bed and thus decreased inability to oxygenate the blood.  So, not only is there less surface area for gas exchange, there is also less vascular bed for gas exchange--but less ventilation-perfusion mismatch than blue bloaters.  The body then has to compensate by hyperventilation (the "puffer" part).  Their arterial blood gases (ABGs) actually are relatively normal because of this compensatory hyperventilation.  Eventually, because of the low cardiac output, people afflicted with this disease develop muscle wasting and weight loss.  They actually have less hypoxemia (compared to blue bloaters) and appear to have a "pink" complexion and hence "pink puffer".  Some of the pink appearance may also be due to the work (use of neck and chest muscles) these folks put into just drawing a breath.

21. Blue Bloater-Chronic Bronchitis is Primary Problem
A "blue bloater" is a person where the primary underlying lung pathology is chronic bronchitis. Just a reminder, chronic bronchitis is caused by excessive mucus production with airway obstruction resulting from hyperplasia of mucus-producing glands, goblet cell metaplasia, and chronic inflammation around bronchi.  Unlike emphysema, the pulmonary capillary bed is undamaged. Instead, the body responds to the increased obstruction by decreasing ventilation and increasing cardiac output. There is a dreadful ventilation to perfusion mismatch leading to hypoxemia and polycythemia.  In addition, they also have increased carbon dioxide retention (hypercapnia).  Because of increasing obstruction, their residual lung volume gradually increases (the "bloating" part).  They are hypoxemic/cyanotic because they actually have worse hypoxemia than pink puffers and this manifests as bluish lips and faces--the "blue" part.
Link to website detailing pathophysiology of emphysema and chronic bronchitis is listed below:

25. Respiratory Damage & Diseases
Figure 17-11b: Surfactant reduces surface tension

26. Factors Affecting Ventilation
Airway Resistance
Diameter
Mucous blockage
Bronchoconstriction
Bronchodilation
Alveolar compliance
Surfactants
Surface tension
Alveolar elasticity
Figure 17-2e: Anatomy Summary

27. Lung Volumes: Spirometer Measurements
Figure 17-12: The recording spirometer

28. Spirometry

29. Efficiency of Breathing: Normal & High Demand
Total Pulmonary Ventilation
(rate X tidal vol about 6 L/min)
Alveolar ventilation
(– dead air space – 4.5 L/min)
Little variation [O2] & [CO2]
Exercise- High Demand
 Depth of breathing
Use inspiratory reserve

30. Efficiency of Breathing: Normal & High Demand
Figure 17-14: Total pulmonary and alveolar ventilation

31. Mucociliary Escalator
Figure 17-6: Ciliated respiratory epithelium

32. Gas Exchange in the Alveoli
Thin cells: exchange
Surfactant cells
Elastic fibers
Recoil
Push air out
Thin basement membrane
Capillaries cover 90% of surface

33. Gas Exchange in the Alveoli
Figure 17-2 h : Anatomy Summary

34. Gas Exchange External Respiration
The exchange membrane components and organization

35. Capillaries in Alveolar Wall

44. Gas Exchange External Respiration
arteriole end
PO2 = 40 mm Hg
PCO2 = 46 mm Hg
PO2 = 100 mm Hg
PCO2 = 40 mm Hg
inspired air O2
pulmonary capillary
alveolus
CO2
expired air
PO2 = 40 mm Hg
PCO2 = 46 mm Hg
PO2 = 100 mm Hg
PCO2 = 40 mm Hg
venule end

46. Gas Exchange Internal Respiration
arteriole end
PO2 = 100 mm Hg
PCO2 = 40 mm Hg
PO2 = 40 mm Hg
PCO2 = 46 mm Hg O2
systemic cell
systemic capillary
CO2
PO2 = 100 mm Hg
PCO2 = 40 mm Hg
PO2 = 40 mm Hg
PCO2 = 46 mm Hg
venule end

48. Gas Exchange What happens when alveolar PO2 drops?
Solubility rules indicate that
If PO2 drops, then the amount dissolved in blood also drops!
Creating a hypoxic condition
Factors that may cause low arterial PO2
Not enough O2 reaching alveoli
Exchange between alveoli and pulmonary capillaries has a problem
Not enough O2 transported in blood

49. Low [O2] in alveoli  vasoconstriction of arteriole
Matching Ventilation with Alveolar Blood Flow (Perfusion)---How does the lung match ventilation with perfusion?
Mostly local regulation using CO2 to control bronchiolar dilation and O2 to control arteriolar dilation
Low [O2] in alveoli  vasoconstriction of arteriole
Reduced blood flow at rest
(lung apex )
saves energy
High blood [CO2]  bronchodilation

53. Matching Ventilation with Alveolar Blood Flow (Perfusion)

57. Ventilation & Gas Exchange Relationship
Net effect of ventilation is to exchange air within the alveoli to
Maintain a partial pressure gradient which is required for gas exchange in the tissues and in the lungs!
Blood flow and ventilation rate are optimized to ensure a usable gradient remains despite changing conditions, this is mainly controlled at the local (lung) level by
the pulmonary capillaries collapse at low bp, diverting blood to areas of the lung with higher bp (away from the apex, towards the base)
Bronchiole diameter is affected by CO2 levels
PCO2 in expired air =  in bronchiole diameter (and vice versa)
Arteriole diameter in the lungs, controlled by blood gas levels
With a  PCO2 and a  PO2, the pulmonary arterioles constrict
With a  PCO2 and a  PO2, the pulmonary arterioles dilate weakly

60. Summary Diaphragm & rib cage are pumps for inspiration
Alveolar surface exchanges O2 & CO2 with blood
The gasses in air act independently & move down a pressure gradient
Airway resistance can limit ventilation efficiency
Typically ventilation matches blood perfusion via local regulators of vasodilation & bronchodilation