Lecture 5 - Breathing Function

Question 1

Respiration and energy equilibrium

Answer 1

• inspiration is active: uses diaphragm contraction
• expiration is passive, doesnt use any energy and tries to return to mechanical equilibrium and restore pressure gradient
• forced expiration requires abdominal muscle contraction - not at equlibrium

Question 2

Normal breathing

Answer 2

• diaphragm contracts and moves downward
• negative pressure in lung compared to mouth, air flows down
• Pulling against: elastic recoil of the chest wall and lung, resistance in airways (size + length of tube determines resistance to airflow)
• negative pressure in the alveoli on inspiration
• expiration - pressure in chest wall wants to go back to equilibrium point: relaxation (chest and lung recoil back)

Question 3

Breathing

Answer 3

• At usual breathing volume, alveoli are smaller at lung base
• lung functions unevenly, due mostly to gravity
• tidal breathing occurs mostly from the lung base
• normal inspiration is active whereas expiration is not
• basal airway tends to close in the elderly

Question 4

Gravitational effects

Answer 4

• creates a different negative pressure in various parts of the lung
• upper lobe: 10 cm H20, lower lober 2.5cm H20
• we breathe mostly from the bottom of our lung because the alveoli are less stretched by gravity cause rest on diaphragm
• top lung more stretched: negative pressure increases

Question 5

Blood vessels are within the alveolar walls - compression

Answer 5

• floppy blood vessels run inside alveolar walls: pressing of capillary when alveoli inflates reduces flow

Question 6

Airways are outside of alveoli: dilate

Answer 6

• dilate when you breathe in
• so inspiration decreases circulation and increases airway space
• decrease in circulation rate favors exchange

Question 7

Pleural pressure

Answer 7

• the airways and blood vessels are affected by pleural pressure
• therefore their calibre and hence function are affected by gravity/posture

Question 8

Lung apices

Answer 8

• alveoli more distended - less ventilation
• blood vessels are more constricted - less perfusion
• ** compared to lung bases
• this is why we breathe more from the bottom of our lungs

Question 9

Pleural pressure - effects on ventilation

Another reason why we breathe with bottom of lung

Answer 9

• lung bases are more compliant - we therefore breathe from the dependent parts of the lung because compliance determines ventilation in normals
• pressure gradient higher in apex : harder to work -> not much breathing
• big changes in l;ung volume where alveoli are small (base of lung)
• highly compliant lung -> very little elastic recoil -> have to fight against little pressure

Question 10

Effects of ageing on lung function

Answer 10

• negative pressure decreases
• lung becomes more compliant as we grow older
• too low negative pressure in base - airway closure - use more the apex of lungs
• lung elastic recoil decreases
• ventilation becomes more uneven
• airway closure increases
• closing volume is earlier

Question 11

• Distribution of ventiltation

Answer 11

• ventilation is inherently heterogeneous
• based mostly on effects of gravity on lung
• ventilation becomes more heterogeneous with age/airway disease
• change in ventilation distribition is an early abnormality of airway disease

Question 12

Mechanical consequences of obstructive airway disease

Answer 12

• airway narrowing
• hyperinflation
• airway closure