Pulmonary ventilation mechanics Flashcards
What is pulmonary ventilation?
The flow of air into and out of the lung alveoli from the atmosphere
What is inspiration?
Breathing in
What is tidal inspiration?
Breathing in at rest
What muscular activities occur during tidal inspiration?
Diaphragm contracts
What happens to the diaphragm when it contracts?
It moves downwards and flattens
What happens to the lungs themselves when the diaphragm contracts?
Diaphragm pulls lower surfaces of lungs downwards
What happens to the volume and pressure of the lungs when their lower surfaces are pulled downwards?
Volume of lungs increases
Pressure of lungs decreases below atmospheric pressure
How does the pressure decrease in the lungs affect the flow of air between the lungs and the atmosphere during inspiration?
Air moves from higher atmospheric pressure into the lungs, which are at a lower pressure
down the pressure gradient
What additional muscular activities occur during forced inspiration?
External intercostal muscles contract
Sternocleidomastoid, scalene and pectoralis muscles contract
How do the sternocleidomastoid, pectoralis and scalene muscles act to move the ribs?
Their other attachment is stabilised
so when they contract, they act on their attachment to the ribs and move the ribs
What happens to the ribs when the external intercostal, scalene and pectoralis muscles contract?
They move upwards and outwards
What happens to the sternum and ribs when the sternocleidomastoid muscle contracts? How?
Sternum moves anteriorly and superiorly by pull of sternocleidomastoid
Ribs moves upwards and outwards by pull of sternum
What happens to the lungs themselves when the external intercostal, sternocleidomastoid, scalene and pectoralis muscles contract?
Chest wall pulls anterior and lateral surfaces of lungs upwards and outwards
Why do the lungs move upwards and outwards as the chest wall does so?
Because the lungs are attached to the chest wall by the pleura
What is expiration?
Breathing out
What is tidal expiration?
Breathing out at rest
What muscular activities occur during tidal expiration?
Diaphragm relaxes
What happens to the diaphragm when it relaxes?
It moves upwards and resumes its normal dome-shape
What happens to the lungs themselves when the diaphragm relaxes?
Lower surfaces of lungs are no longer pulled downwards
elastic recoil of lungs moves them back up
What happens to the volume and pressure of the lungs when the lungs recoil?
Volume of lungs decreases
Pressure of lungs increases above atmospheric pressure
How does the increase in pressure in the lungs affect air flow between the lungs and atmosphere during expiration?
Air moves from the higher pressure in the lungs to the lower pressure in the atmosphere
down the pressure gradient
What additional muscular activities during forced expiration?
External intercostal muscles relax
Internal intercostal and abdominal muscles contract
What happens to the ribs when the external intercostal muscles relax and the internal intercostal muscles contract?
Ribs move downwards and inwards
What happens to the lungs themselves when the external intercostals muscles relax and the internal intercostal muscles contract?
Chest wall no longer pulls anterior and lateral surfaces of lungs upwards and outwards
elastic recoil of lungs moves them back down and in
What happens to the lungs themselves when the abdominal muscles contract?
Abdominal muscles push contents of abdomen upwards
push diaphragm upwards
compress the lungs upwards
What are the pressures in the pleural space?
Inspiration = -7mmHg
Expiration = -3mmHg
Why is the pressure in the pleural space negative?
Because the parietal pleura and visceral pleura are pulled in opposite directions
What direction is the parietal pleura pulled in? How?
Outwards by the chest wall wanting to spring outwards
What direction is the visceral pleura pulled in? How?
Inwards by the elastic recoil of the lungs
Why does the pressure in the pleural space become more negative with inspiration?
Chest wall moves upwards and outwards
pulls on parietal pleura even more
increases volume of space in pleural space, decreasing pressure
What is meant by compliance?
The ability of the lungs to distend
What is the equation for compliance?
Change in lung volume
____________________
Change in pleural pressure
What volume and pressure changes occurs in lungs with low compliance?
Low compliance means need bigger decreases in pleural pressure
to pull the lungs
and increase their volume
What volume and pressure changes occur in lungs with high compliance?
High compliance means need smaller decreases in pleural pressure
to pull the lungs
and increase their volume
What are the factors affecting compliance of the lungs?
Elastic recoil
Fibrosis
How does elastic recoil of lungs affect lung compliance?
Need bigger decreases in pleural pressure to pull the lungs and increase their volume
therefore decreases lung compliance
What causes the elastic recoil of the lungs?
Elastin fibers in the lung tissue
Surface tension
What is the biggest cause of elastic recoil of the lungs?
Surface tension
How does elastin in the lungs change with age?
Decrease in amount of elastin
What is Laplace’s law?
Pressure = 2 x surface tension / radius
Pressure generated by the alveolar elastic recoil
What is surface tension?
When water is in contact with air
the water molecules at the surface are strongly bonded to each other
they attempt to move closer to each other to minimise the surface area
Where does surface tension occur in the lungs?
Alveoli
How does surface tension occur in the alveoli?
Water on inner surface of alveoli
What are the effects of surface tension in the alveoli?
Makes the alveoli collapse
smaller ones into larger ones
Why would smaller alveoli collapse into larger alveoli, as opposed to them evening out?
Smaller alveoli have smaller radius than larger ones
therefore have higher pressure than larger ones
air moves from higher pressure to lower pressure down the pressure gradient
What does surfactant stand for?
Surface active agent
What is surfactant made up of?
Complex mixture of lipids and proteins
Where is surfactant found in the lungs?
Alveoli
What is responsible for the surfactant found in the alveoli?
Type 2 pneumocytes
When does surfactant production in the alveoli begin?
25-28 weeks of gestational age
When is the amount of surfactant in the alveoli sufficient?
35 weeks of gestational age
What is the effect of surfactant on surface tension?
Decreases surface tension
How does surfactant decrease surface tension?
Surfactant spreads over inner surface of alvoeli
separates the water molecules at the surface from each other
How does surfactant affect the alveoli?
Prevents the smaller ones from collapsing into the larger ones
How does surfactant prevent smaller alveoli from collapsing into larger alveoli?
Surfactant molecules spread over inner surface of larger alveoli more thinly, less effective
surface tension decreases less
pressure decreases less
equivalent to that of smaller alveoli
How does surfactant affect lung compliance?
Reduces elastic recoil of lungs
need smaller decreases in pleural pressure to pull the lungs and increase their volume
therefore increases lung compliance
What is the cause of respiratory distress syndrome of the newborn?
Babies born prematurely before 30 weeks
have less surfactant in their alveoli, increased surface tension, alveolar collapse
What are the signs of respiratory distress syndrome of the newborn?
Intercostal and subcostal recession
Why is intercostal and subcostal recession seen with respiratory distress syndrome of the newborn?
Reduced pressure in the lungs
draws overlying attached muscles and skin inwards
How is respiratory distress syndrome of the newborn treated?
Surfactant replacement
Oxygen
Assisted ventilation
If yet unborn, give glucocorticoid treatment to mother because it increases surfactant production in the foetus
