Mechanics of breathing Flashcards
What does Boyle’s Law state?
At a given temperature, the pressure and volume of an ideal gas are inversely proportional
Name the 4 accessory muscles of forced inspiration.
Sternocleidomastoid
Scalene muscles
Pectoralis major
Latissimus dorsi
Name the 3 muscles of forced expiration.
Abdominal muscles
Internal intercostal muscles
Innermost intercostal muscles
Is the pleural space a higher or negative pressure compared to atmospheric pressure?
Negative
What prevents our lungs from collapsing?
The negative pressure in the pleural cavity (negative intrapleural pressure)
Which 3 factors create a negative intrapleural pressure?
Elastic recoil of the lungs
Surface tension
Outward recoil of the chest wall
What is transpulmonary pressure?
The pressure difference between intrapulmonary pressure and intrapleural pressure
What is the usual value of transpulmonary pressure?
Transpulmonary pressure = intrapulmonary pressure – intrapleural pressure
0 – (-4) = 4mmHg
How is lung compliance calculated?
Compliance = change in volume / change in transpulmonary pressure
The elastic properties of the lung are due to which 2 components?
Elastin + collagen fibres
Surface tension
Where in the lungs is intrapleural pressure more negative, the apex or base?
What causes this?
Apex
The effect of gravity pulling the lung downwards, causing higher volume at the apex of the lung and therefore less pressure than at the base
Where in the lungs is there a greater transmural pressure gradient, the apex or base?
Apex
Describe the apex and base alveoli in terms of size and compliance.
Apex – larger alveoli, less compliant
Base – smaller alveoli, more compliant
Where in the lungs is ventilation greatest, apex or base?
Base
Surface tension at the air-fluid interface in the alveoli creates what kind of pressure?
An inward collapsing pressure
Describe the equation of Laplace’s Law.
Pressure in a bubble = 2 x surface tension / radius
Which size alveoli require a higher pressure to stay inflated, big or small?
Small alveoli
Which 2 factors help to stabilise alveoli?
Alveolar interdependence – Pores of Kohn + canals of Lambert
Surfactant
How and where is surfactant secreted from?
Exocytosis
Type II pneumocytes
By what mechanism does surfactant decrease surface tension?
Disrupts hydrogen bonds between surface water molecules
Define the work of breathing.
The energy consumed by the respiratory muscles during the respiratory cycle
The work of breathing consists of which 2 components?
Elastic work
Resistive work
What is elastic work in breathing?
The energy required to overcome the elastic recoil of the lungs and chest wall during inspiration
What happens to some of the energy used in elastic work of breathing?
Stored as potential energy and used in expiration
What is resistive work in breathing?
The energy needed to overcome airway resistance during ventilation
What happens to the energy used in resistive work?
Energy is ‘wasted’ as heat and sound
What element(s) of work of breathing is affected in obesity and how?
Increases elastic work of breathing – opposes the outward elastic recoil of the chest wall
What element(s) of work of breathing is affected in pulmonary fibrosis and how?
Increases elastic work of breathing – lung tissue is replaced by scar tissue which means the lungs are stiffer and reduces lung compliance
Increases resistive work of breathing – increased amount of lung tissue increases tissue resistance
What element(s) of work of breathing is affected in asthma and how?
Increases resistive work of breathing – airway narrowing due to bronchoconstriction and mucosal oedema increases airway resistance
What are the 2 main factors affecting airway resistance?
Turbulent air flow
Change in airway radius
Describe dynamic airway compression.
During forced expiration, intrapleural pressure can become positive, causing collapse of airways without cartilage in their walls e.g. bronchioles. This can be worsened in disease which cause airway narrowing or loss of elastic tissue
Which 2 muscles are involved in quiet (tidal) breathing?
Diaphragm
External intercostals
How does intrapleural pressure change during inspiration?
Becomes more negative
How does intrapleural pressure change during expiration?
Becomes less negative
During inspiration, what changes occur in intrapleural and transpulmonary pressure?
Decreased intrapleural pressure
Increased transpulmonary pressure
During expiration, what changes occur in intrapleural and transpulmonary pressure?
Increased intrapleural pressure
Decreased transpulmonary pressure
How does elasticity and compliance change in emphysema?
Decreased elasticity
Increased compliance
How does elasticity and compliance change in pulmonary fibrosis?
Increased elasticity
Decreased compliance
When is compliance highest in terms of lung volume?
Low long volumes
When is compliance lowest in terms of lung volume?
High lung volumes
Which type of epithelium are type II pneumocytes?
Cuboidal
Dynamic airway compression occurs during which type of breathing?
Forced expiration
