Respiratory Mechanics and Lung Volumes Flashcards
what is each lung surrounded by
visceral pleurae
what do the lungs “sit” in
water-filled pleural sacs
what surrounds the chest wall (rib cage, sternum, thoracic tissue and intercostal muscles) and diaphragm
parietal pleura
parietal and visceral pleura in a healthy person
stuck with water lining.
the space between them is called called the pleural cavity and its filled with intrapleural fluid - its not a real space
why is the pleural cavity at lower than atmospheric pressure at rest (relaxed, when not breathing in or out)
even with surfactant molecules the avioli still have an inward water surface tension, which pulls the visceral pleura that surrounds them in, making the pleural cavity slightly larger and slightly decreasing its pressure (since it doesn’t have a connection to the atmosphere - closed in system)
don’t need to know this but also elasticity of lungs (tendency to collapse lungs) and chest wall (tendency to expand lungs)
another side note lymphatic vessels drain the fluid in pleural cavity so that it maintains pressure and doesn’t weigh on the lungs
what is the transmural pressure gradient and why is it important
negative pressure that holds the visceral and parietal pleura together
forces wanting to recoil or collapse lung are stronger than ones that want to expand it
if pressure is equalised to atmospheric, the lungs would collapse (because lower pressure allows higher pressure alviolar area to expand and oppose collapsing forces)
how does pneumothorax look visually
ribs would protrude (pop out) as no force holding them in anymore (pleural cavity becomes a real cavity, so parietal and visceral pleura are no longer connected, no tension)
Q problems in premature babies and intrapleural pressure
type II cells don’t produce enough surfactant molecules
greater water tension on alveoli, increased pressure of pleura cavity
lung would shrink more than normal since transpulmonary pressure is increased (ask about this dont really get which one is stronger, aka . is this difference in pressure as strong as the surface tension? doesn’t it account for the ack of surfactant molecules)
what does the lung do in quiet breathing (hint: during exhalation)
recoil passively
what is airflow rate equal to
pressure gradient / airway resistance (size/diameter of airways, cased by friction molecules experience along airway walls)
why is pressure lost along the airway
due to airway resistance and bronchioles above alveoli level also being subject to intrapleural pressure
this lower pressure also keeps these vessels from collapsing
side note large airways surrounded by cartilage rings are outside of the intrapleural space
what happens to intrapleural pressure during forceful exhalation
intrapleural pressure is increase up to 786 or positive 26
excepting pressure on the alveoli and upper level bronchioles, causing them to push air out more rapidly
lungs are contracted before they fully expand
what is dynamic small airway closure !!!
when the elevated intrapleural pressure during forceful exhalation starts to equal the pressure within small airways on the way to the lungs, closing those airways (as they don’t have cartilage around them) restricting breathing
at end of forced expiration there is always some leftover air in alveoli - residual volume
forceful expiration in asthmatic people
pressure within alveoli and small vessels is lost quicker, reaching equilibrium with the high intrapleural pressure sooner, meaning there is more air left in lungs
causes air trapping
what is anatomical dead space (airway dead space) and how is it significant when you breathe out
volume of inhaled air that does not take part in the gas exchange, when alveoli are full some air about 150 mL is left in the small bronchioles or airways
first 150 mL you breathe out is the fresh air that was sitting in your airways, only 350 ml of old alveoli air is actually expelled, 150 of old remain is dead space
those 150 ml of old air is than inhaled
