ventilation and compliance Flashcards
what is residual volume and why is it important?
it is the volume of air that stays in a person’s lungs after fully exhaling. It stops the alveolar from collapsing and allows for gas exchange between breaths
what does a lung capacity value mean?
it is a sum of 2 or more volumes
what is total lung capacity?
everything including residual volume, tidal volume, expiratory and inspiratory reserves
what is the anatomical dead space volume and what is it in general?
150 ml
air that doesn’t participate in gas exchange but fills conducting airways
what is the average tidal volume and what does it mean?
500 ml on average
ie we breathe in 500 ml of air and breathe out 500 ml of air
no matter how much you squeeze your lungs to let air out you are always going to breathe out this tidal volume
what is vital capacity?
max amount of air you can expel from the lungs after a max inhalation.
ie. inspiratory reserve volume (what you take in to get max breath) + tidal volume (always there) + expiratory reserve volume (air that you can let out if you need to)
What does ventilation mean?
the movement of air in and out of the lungs
pulmonary ventilation
total air movement into/ out of the lungs - doesn’t tell us anything about dead space
alveolar ventilation
amount of fresh air getting to alveoli and therefore available for gas exchange
Dalton’s Law
total pressure of a gas mixture is the sum of pressures of the individual gases
what is partial pressure? units?
pressure of a gas in a mixture of gases is equivalent to the % of that particular gas in the entire mixture multiplied by the pressure of the whole gaseous mixture
mmHg or kPa units
why does the body get rid of CO2?
it is poisonous to cells
CO2 is the main reason you hyperventilate ie to get it out of the body
we produce CO2 it is not obtained from the air we breathe
PO2 and PCO2 stand for what?
partial pressure of oxygen and CO2
what happens at end of inspiration?
350 ml of fresh air goes into alveoli
150 ml fresh air enters DEAD SPACE
what happens at the end of expiration?
dead space is filled with STALE air
what happens to P02 and Pc02 during hypo-ventilation?
P02 falls (30) Pc02 rises (100)
what happens to P02 and Pc02 during hyper-ventilation?
P02 rises (120) PC02 falls (20)
what are the normal ventilation values for PO2 and PCO2
PO2 100
PCO2 40
these remain fairly constant in resting alveolar ventilation
what do type 2 alveolar cells produce and what does it do?
surfactant fluid
it reduces surface tension on alveolar surface membrane which reduces the tendency for alveoli to collapse
define compliance
change in volume relative to change in pressure i.e. how much does volume change for any given change in pressure
what does compliance represent?
stretchability of the lungs ie how to get air in by stretching open, it tells us nothing about getting air out
what is surface tension?
when water molecules line the alveoli they create an inwardly directive force that makes the alveoli want to collapse. During inspiration this needs to be overcome as air needs to fill the alveoli.
how does surfactant reduce surface tension
surfactant sits between water molecules and reduces the attraction between the water molecules therefore decreasing the inward force and preventing the alveoli from collapsing.