Mechanisms of Breathing Flashcards
What do changes in lung volume induce?
→ Changes in alveolar pressure which generate pressure gradients between alveoli & atmosphere, causing air to flow.
why any differences in pressure between the alveoli and atmosphere not instantly negated by the movement of air?
There is a delay due to the time taken for air to move.
What does rate of airflow depend on?
pressure gradient & level of airway resistance
Ohm’s law…
𝐴𝑖𝑟𝑓𝑙𝑜𝑤 (𝑉) =(Δ𝑃𝑟𝑒𝑠𝑠𝑢𝑟𝑒 (𝑃))/(𝑅𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒 (𝑅)
Hagen-Poiseuille equation…
𝑅𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒 (𝑅) ∝ 1/𝑟𝑎𝑑𝑖𝑢𝑠^4
What happens to resistance as airway radius increase?
→the resistance increases (and the airflow decreases) dramatically
What are some causes of reduced airway lumen?
→Contraction of airway smooth muscle, →excessive mucus secretion, →oedema/swelling of the airway tissue, →damage to the integrity of the airways structure (i.e. loss of patency
When does turbulent airflow occur?
→where high velocities of airflow are achieved (e.g. during forced breathing manoeuvres)
→if there is a sudden decrease in luminal area such as in obstructed airways.
What produces the wheezing sound?
The vibration generated by the turbulent airflow
What is patency?
the state of being open or unobstructed; a ‘loss of patency’ = closing/obstruction
How are open structures maintained?
by elastic fibres within the wall of the airway and radial traction.
→the airways are pulled open by their connections to the surrounding tissue
How can intrapleural space reduce airway patency?
When intrapleural pressure becomes positive (as can occur during forced expiration), collapsing force will be exerted onto the airways
→In healthy individuals, the structural integrity of the airways is sufficient to prevent collapse
Why is decreased structural integrity of the airways problematic in COPD?
the simultaneous loss of elastic recoil within the lung tissue means that both radial traction of the airways and lung recoil and reduced.
→greater force is required to compress the lungs during expiration,
→however the more force that is exerted to maintain ventilation and airflow, the more obstructed the patient’s airways will become
How is transpulmonary pressure calculated?
(Ptp = Palv – Pip)
What is lung compliance?
→relationship between the change in lung volume produced by a particular changed in transpulmonary pressure
→describes how easily the lungs can be distended
What does high and low compliance mean for elastic recoil and force required to inflate, and volume change?
Higher lung compliance = less elastic recoil = less force required to inflate = ↑ volume change per pressure change (↑gradient on volume-pressure curve)
Lower compliance = more elastic recoil = more force required to inflate = ↓volume change per pressure change (↓ gradient on volume-pressure curve)
Equation for compliance
volume/pressure
How do you calculate lung compliance from a graph?
by a graph of lung volume vs. transpulmonary pressure,
→as lung compliance = the gradient of the curve
What is the difference between static and dynamic compliance?
static= measurements taken whilst airflow =0, the steepest part of the curve is used
dynamic=measurements taken in the presence of airflow, the gradient between the end tidal inspiratory and end tidal expiratory points is used
How does scoliosis affect compliance?
reduction
→ through chest wall mechanics
How does neonatal respiratory distress syndrome affect compliance?
reduction
→ through alveolar surface tension
How does fibrosis and COPD affect compliance?
reduction
→ through collagen deposition
COPD:
increases compliance
What is emphysema?
involves degradation of elastin fibres making the lung less stiff and more complaint but reducing recoil
What is pulmonary fibrosis?
scarring and deposition of structural fibres such as collagen making the lung stiff and less compliant.
How is a bubble created?
The water-air interface formed between the lining fluid and pseudo-spherical alveolar airspace
How does surface tension arise within a bubble?
due to the relative strength of hydrogen bonds between water molecules combining to exert an overall collapsing force toward the centre of the bubble.
What is Laplace’s law and how is it associated with pressure?
The amount within a specific bubble is described by the Law of Laplace
→𝑃 =2𝑇/𝑟 Pressure →Surface tension (e.g. water = 0.075N/m) Radius of bubble (i.e. alveoli) →(The smaller the alveoli, the larger the pressure generated)
Q: What would happen if 2 bubbles of different radius were connected to each other (e.g. different size alveoli connected via airways)?
Pressure gradients would be created between different sized alveoli, resulting in smaller alveoli emptying into larger ones
→This would thus make inflation of the lung very difficult
How is the potential problem of smaller bubbles lowering into larger ones resolved?
→by the presence of pulmonary surfactant
→acts to disrupt the attractive forces between water molecules, reducing surfacing tension and the collapsing pressure generated
What are surfactants?
→phospholipoprotein secreted by type II pneumocytes (alveolar cells
→amphipathic, will naturally position themselves at the air-liquid interface.
How do surfactants equalise pressure between varying alveoli sizes?
→As alveolar size increases during inflation, the concentration of surfactant molecules at the interface decrease
→surface tension (and thus pressure generated) increases with increasing alveolar surface area.
→air will naturally flow from larger (more inflated) alveoli to smaller ones, helping to distribute air across the lung during inspiration
How does surfactants tension reduce alveolar oedema?
→reduces hydrostatics pressure in the alveolar tissue.
→acts to pull fluid out of the surrounding pulmonary capillaries and into the alveoli and interstitial tissue. →By reducing surface tension, pulmonary surfactant helps to prevent alveolar oedema due to excessive fluid being pulled from capillaries
What is the neonatal respiratory distress syndrome?
→Premature birth, maternal diabetes, congenital developmental issues
→Insufficient surfactant production
→Stiff (low compliance) lungs, alveolar collapse, oedema
→Respiratory failure
→Hypoxia
→Pulmonary vasoconstriction, endothelial damage, acidosis, pulmonary + cerebral haemorrhage.
→innervating capillaries
How is NRDS treated?
→supplementation of affected infants with artificial surfactant
→ maternal administering glucocorticoids (which increase surfactant production via maturation of type 2 pneumocytes) t
What happens with saline filled lungs ex vivo?
lungs required less pressure to inflate (↑ compliance)
What happens with washed lungs then inflation?
produced lungs that required more pressure to inflate (↓ compliance).
