mechanisms of breathing, pressures & work Flashcards
when we inspire how much does the diaphragm change by?
75% change in volume
what muscles are used to inspire?
scalene & sternomastoids
what causes an increase in intrathoracic volume?
contraction of inspiratory muscles
what kind of process is inspiration?
an active process
describe the process of inspiration
- contraction of inspiratory muscles
- this caused a decrease in intrapleural pressure
- lungs are pulled into more expanded position and the pressure in the airway becomes more negative so air moves in
- at end of inspiration pressures are equal
- recoil of lungs and chest wall can then occur
what is trans pulmonary pressure?
when the chest wall exerts a distending pressure on the pleural space, which is transmitted to the alveoli to increase its volume, lower its pressure and generate airflow inwards
what is compliance?
the static measure of lung stretchiness
what is the balance point of compliance?
functional residual capacity (FRC)
what are the end points of compliance?
total lung capacity (TLC) & residual volume (RV)
why do the lungs tend to collapse?
trans pulmonary pressure is positive from RV to TLC
why does the chest wall tend to spring out?
transthoracic pressure is negative at RV and FRC
what does the compliance of the lung depend on?
depends on how inflated the lung is or not
what is the difference between the compliance curves of inspiration and exhalation called?
hysteresis
is the lung less or more compliant at higher volumes?
lung is less compliant
what does loss of elastic recoil lead to?
the lungs become easy to inflate but difficult to exhale
what does increase in elastic recoil lead to?
becomes difficult to inflate the lungs
what factors cause surface tension to increase?
emphysema and age
what do type II alveolar cells do?
extract fatty acids from blood and synthesise surfactant
why is surfactant important?
- increases lung compliance because surface forces are reduced
- promotes alveolar stability
- prevents alveolar collapse
- surface tension tends to suck fluid from capillaries into alveoli
where does airway resistance originate from?
friction between air and mucosa
what is airway resistance?
the pressure difference between the alveoli and mouth divided by the flow rate
what is the airway resistance equation?
pressure 1 - pressure 2 / flow
what is pulmonary resistance
tissue + airway
what is laminar flow?
smooth flow, the resistance generated is proportional to the radius
what is turbulent flow?
irregular, chaotic, with eddie currents, it is good for transferring heat but the resistance is high
what is the “Reynold’s number” for?
it helps to predict when laminar flow converts to turbulent flow
what factors affect airway resistance?
- inflammation
- mucus
- bronchodilators
- steroids
- gas density
what is elastic work?
- decreased elasticity in restrictive diseases
- greater WOB
what is non elastic work?
obstructive diseases lead to greater WOB to overcome increased airway resistance
