mechanism of breathing Flashcards
whats the main law we are following in the breathing cycle?
boyles law = low volume = high pressure –> expiration
high volume = low pressure —> inspiration
P1V1 = P2V2
whats the main muscle responsible for inspiration
diaphragm
intercostal muscles are accessory
forced inspiration : scalene, sternocleidomastoid
whats the main muscle for expirations?
no muscle its passive
in forced expiration its abdominal muscles ( they increase abdomen pressure which pushes the lung ups and reducing their volume and increasing their pressure )
how does the air diffusion works?
air moves in pressure gradient from high to low pressure
whats the nerve supply of diaphragm?
phrenic nerve c3-c5
whats transmural pressure?
pressure difference between the lung walls
transpulmonary
transthoracic
transrespiratory
whats transpulmonary pressure?
transpulmonary pressure = Interpulmonary pressure - interpleural pressure
its always positive
whats transthoracic pressure?
transthoracic pressure = interpleural pressure - atmospheric pressure
Should be negative
whats transrespiratory pressure?
transrespiratory pressure = interpulmonary pressure - atmospheric pressure
whats transairway pressure?
pressure difference across the airway
Transairway pressure = pressure in airway - pressure in pleura
why is the transpulmonary pressure is always positive ?
because its the intrapleural is negative why?
1- elastic recoil –> lungs have natural tendency to collapse
2- surface tension –> pleural fluild
3- elasticity of chest wall –> wall wants to expand
when we say interpulmonary pressure is 0 it means its equal to atmospheric so when we calculate transpulmonary it will be like : 0 - ( -4) = 4
whats the tendency of the chest wall?
tends to expand so there will be 2 forces on the pleural :
paratial layer will be pulled by chest wall
visceral layer will be pulled by lung to collapse
in opposite directions
what does it mean when transpulmonary pressure is 0
it means pneumothorax because its not negative and intrapleural is 0 = LUNG COLLAPSE
whats the sequence of events in normal inspiration?
1- inspiratory muscle contracts
2- Thoracic expands = more volume = less pressure
3- Pleural becomes more negative
4- Transpulmonary pressure increases because - - is positive
5- lungs inflate
6- alveolar pessure becomes less than atmosphere
7- air comes to the lung and fill it up until pressure is back to normal
what happens to the intrapleural pressure during inspiration cycle?
becomes more negative then goes back to normal
whats the maximum amount of air volume can be taken in by lungs?
6000 or 6 liters
whats residual volume?
air in the lung you can you cant get rid of which 1000 or 1 LITER
whats inspiratory reserve volume?
maximum amount of air you can inhale above tidal volume from 500 to 6000
whats expiratory reserve volume?
volume of air you can expire more than tidal volume which is more than 500 but cant go below 1000
whats tidal volume?
amount of air going in and out of the lung with normal quiet breath cycle
usually the lung goes from 2500 to 3000 and back to 2500 so its usually 500
whats a capacity ?
capacity is calculated by adding 2 volumes together
whats total lung capacity?
you add all of the volumes, TV + IRV + ERV + RV
whats inspiratory capacity?
maximum air you can inhale so you add IRV + TV
whats vital capacity?
maximum amount you can exhale out so you add all of them except RV cuz you cant exhale it out so
TV + IRV + ERV
you dont add RV cuz cant exhale it out
whats functional residual capacity?
the amount of the air inside the lung after normal quiet expiration
RV ( amount of air already in the lung ) + ERV ( amount you exhaled normally )
mnemonic
RV
ERV
IRV
TV
First two = Functional residual capacity
last two = inspiratory capacity
last 3 = vital capacity
all = total lung capacity
what lung volumes and capacities that cannot be measured via spirometry?
RV
FRC = RV + ERV
TLC = all
whats other way of measuring RV and FRC?
helium dilution technique
what determines what you are measuring in helium dilution technique
the time you start the test at
what are you measuring at the end of normal tidal volume ( end of expiration )
Functional residual capacity
what are you measuring at the end of forced vital capacity? ( most air you can exhale all except rv)
you are measuring RV because thats whats left in the lung after you exhale everything else out
whats the limitation of the test?
gives false FRC in some diseases
whats body plethysmograph used for?
measuring of FRC
whats the most useful measurements that comes from spirometer?
VC and FVC ( amount of air you can exhale out : TV + IRV + ERV
whats FEV ?
forced expiratory volume of air exhaled in 1 second
whats FEV/FVC ratio?
the amount of air you can forcefully exhale in 1 second in relation to the total amount of air you can exhale ( FVC)
usually its 0.8 or 80% normal and useful diagnosis of some diseases
how do you measure FVC and FEV1?
ask the patient to inhale as much air as possible then exhale all what they inhaled , usually it takes 3 seconds to exhale all what that has been inhaled
then we do the same and measure what comes out in the first second only
what does the FEV/FVC in obstructive diseases like asthma looks like?
it will be less because very little amount of air comes out in the first second due to obstruction
so decreased FEV and less ratio
what does FEV/FVC in restrictive disease look like? example fibrosis?
there will be limited recoil so the FEV will be very high compared to normal and FVC will be less because theres abnormal recoil so increased FEV and increased FVC = increased ratio
the problem is not pathway its the the lungs itself
