Mechanics of breathing 1 Flashcards
Describe the ‘active process’ of inspiration vs the ‘passive’ expiration
- inspiration is an active process - which occurs due to the contraction of the inspiratory muscles
- expiration is a passive process that occurs due to the elastic recoil of the lungs
What occurs as a result of the contraction of the inspiratory muscles?
- contraction expands the thoracic cavity which leads to a decreased intrapleural pressure
- the drop in intrapleural pressure** helps the lungs to expand**
- the expansion of the lungs** decreases intrapulmonary pressure to sub-atm level **to which air from the atmosphere is sucked into the lungs
What is Boyle’s law?
- the pressure (P) exerted by a constant number of gas molecules in an enclosed space is** inversely proportional** to the volume (V) of the container
How does air move in bulk flow in terms of pressure
air moves in bulk flow from areas of high pressure to one of low pressure
What is flow (F) equal to?
- the pressure difference between 2 points (delta P) and inversely propotional to the resistance
What is the equation for flow (F)?
F= delta P/R
ie F = Palveolar - Patm/R
What is the pleura?
- The pleura is a 2 layered membrane - the parietal and the visceral pleura
- it functions to reduce any friction between the rib cage, lung and chest cavity
What are the main muscles associated with inspiration?
- Diaphragm
- External intercostal muscle
What are the main muscles involved in expiration?
- Internal intercostal
- pectoral muscle
- abdominal muscles
What happens to the abdominal contents when the diaphragm contracts?
- the abdominal contents are forced downwards and forwards
What happens to the ribs when the diaphragm contracts?
the rib margins are lifted and move outwards
Where are the external intercostal muscles present?
they are present between ribs in a forward and downward direction
What 2 effects does contraction of external intercostal muscles?
- bucket-handle effect : increases the transverse diameter of the thoracic cavity
- pump-handle effect: increases the vertical diameter of the thoracic cage
What are important ‘accessory’ muscles for inspiration?
- scalene muscles - muscles attaching cervical vertebrae to first and second rib
- pectoralis major - muscles attaching thoracic cage to upper limb
What is the function of the scalene muscle during inspiration?
- elevates 1st and 2nd rib’s
Describe the sequence of active inspiration
- inspiratory muscles contract
- lung volume increases
- alveolar pressure** decreases **
-
alveolar pressure is less than atm pressure
5.** air flows into** the lungs
Describe the basic sequence of expiration (passive)
- relaxation of inspiratory muscles
- lung volume decreases
- alveolar pressure increases
- alveolar pressure is greater than atm pressure
- air flows out of the lung
What are 3 pressures of the thoracic cavity
- **intrapleural **pressure
- transpulmonary pressure
- alveolar pressure
what is intrapleural pressure?
- the pressure in the pleural space
- ie the space between the lungs and the chest wall (the virtual space between the visceral and parietal pleura)
what is the normal value (during quiet breathing) of intrapleural pressure ?
-2.5 to -4mm of Hg
what is transpulmonary pressure?
- the measurement is the pressure difference between the alveolar space and the intrapleural space
what is the function of the transpulmonary pressure?
keeps the lungs inflated and prevents the lungs from collapsing
what is the alveolar pressure?
- the pressure inside the alveoli
- the change in alveolar pressure moves air in and out of the lungs
what happens to the alveolar pressure during inspiration?
- alveolar pressure decreases which sucks air into the lungs
what happens to the alveolar pressure during expiration?
the alveolar pressure increases, removing air from the lungs
what is the normal value for alveolar pressure during inspiration & expiration?
Inspiration :-1mmHg
expiration: +1mmHg
