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.
when does surfactant production start? and describe it
about 25 weeks gestation
it is stimulated by thyroid hormones and cortisol which increase towards end of pregnancy
what is IRDS and why are premature babies at risk of this
infant respiratory distress syndrome
due to insufficient surfactant production and structural immaturity in the lungs.
where happens to air in smaller alveolus when there is no surfactant?
it flows into the larger alveolus and therefore collapses losing that surface area
what is the law of LaPlace equation and what does it mean?
P=2T/r P= pressure T= surface tension r= radius it describes the pressure required to keep alveoli open
when surfactant is present what happens to the pressure in the large and small alveoli
they become equal
where is pressure greater? the smaller or larger alveolus?
in the smaller alveolus
high compliance
large increase in lung volume for small decrease in ip (interstitial pressure - pressure in pleural space) pressure
ie a lot of air getting into alveoli in a smaller breath (not much decrease in thoracic pressure)
low compliance
small increase in lung volume for large decrease in ip pressure (ie not much O2 getting to alveoli in a large breath)
visceral pleura
the portion of protective tissue that is attached directly to the lungs
parietal pleura
portion of the protective tissue that lines the inner surface of the chest wall and covers the diaphragm
visceral pleura
portion of protective tissue that is attached directly to the lungs
what is emphysema
a loss of elastic tissue (recoil) means expiration requires effort
what is emphysema
a loss of elastic tissue means expiration requires effort
what is fibrosis
inert fibrosis tissue means effort of inspiration increases- harder to get air in as scar tissue thickens walls and oxygen can’t diffuse across as easily
what is compliance like at the apex of the lung and why?
lowest compliance at the apex of the lung because the weight of the lung pulls the lung downwards stretching open the alveoli at the apex meaning their ability to change volume isn’t good
what is compliance like at the base of the lung and why?
highest compliance to ventilation
because the weight of the lung compresses the alveoli against the diaphragm so their ability to change volume on inspiration is better.
obstructive lung disease
obstruction of air flow, especially on expiration
restrictive lung disease
restriction of lung expansion
examples of obstructive lung diseases
asthma
COPD
asthma
over-reaction of bronchial smooth muscle which reduces the diameter of the airways and reduces the ability to get air out
COPD
Chronic Obstructive Pulmonary Disease
Chronic bronchitis - Inflammation of the bronchi
Emphysema -Destruction of the alveoli, loss of elasticity
examples of restrictive lung diseases
loss of lung compliance- lung stiffness or incomplete lung expansion fibrosis infant respiratory distress syndrome oedema pneumothorax
what is oadema of the lung
fluid building up between alveoli, creating space reduces diffusion
what is pnuemothorax
punctured lung so air seeps into thorax leads to collapsed lung
spirometry
technique used to measure lung function
FEV1 and FVC are measured from a full forced experiation into a spirometer. Exhalation continues until no more breath can be exhaled
FEV1/FVC ratio then gives a good estimate of the severity of airflow obstruction
static measurement (Lung volumes that are not affected by the rate of air movement in and out of the lungs ie tidal vol etc)
only consideration made is the volume exhaled
dynamic
time taken to exhale a certain volume is what is being measured- more helpful
FEV1
forced expiratory volume in 1 second
spirometry in obstructive lung disease
you have restricted air flow so FEV1 dramatically reduces ie the amount of air you can get out in 1 second reduces because there is a real problem with getting air out the lung
spirometry in restrictive lung disease
reduction in FVC because there is a problem with lung expansion the total amount of air in lung will be less so although there is no problem getting air out, there is less air in the first place
FVC
forced vital capacity
is the total amount of air exhaled during the FEV test.
norm ratio of FEV1/FVC
80%
why is surfactant more effective in small alveoli than large?
surfactant molecules come closer together and are therefore more concentrated.
is high compliance healthy lungs or poor lungs?
healthy
when is high compliance bad?
if it doesn’t come with high elasticity
what can spirometer not measure?
residual volume as that is always in your lungs
