lecture 25- resp Flashcards
At an air-fluid interface, the surface is under a
tension bc of attractive forces between fluid molecules
–> inwardly directed pressure
Law of laplace
P= 2T/r
P= pressure
T= surface tension of the fluid
how does surfactant allow alveoli to expand?
by decreasing the tension, which decreases the inward pressure
what would happen to alveoli without surfactant?
inward pressures of alveoli would be high.
prone to inflation and collapse
smaller alveoli have more
surfactant
how is pressure and air flow distributed in alveoli
equally
functional residual capacity (FRC)
volume of air left in the lungs after a normal expiration
Positive transpulmonary pressure
is the force inflating the lungs
what keeps the lung adhered to the chest wall?
pleural fluid
pneumothorax
air enters the pleural sac, intrapleural pressure is not negative anymore
bond holding lung to chest wall is broken and lung collapses
pneumothorax= “air in the thorax”
chest expansion — Pip
causes decreased intrapleural pressure
(V increases, pressure decreases)
Transpulmonary pressure equation
Palv-Pip
the difference between the pressure in the alveoli and the pressure in the pleural cavity
Compliance: lung
ability of the lungs to stretch (change volume for a given pressure)
when is compliance decreased?
in restrictive pulmonary diseases
ex. fibrosis
elastance
the ability of the lung to spring back after being stretched
what allows lung elastance
the presence of elastin fibers in the lung interstitial space
when is elastance decreased?
in emphysema (loss of elastin)
high compliance of the lung allows them to
move outward with little force required
elastic recoil of the lung creates
an inward pull
Boyles law
P1V1=P2V2
what happens when inspiratory muscles contract (boyle’s law)
lung volume increases, pressure in lungs decreases, air is ‘sucked’ into the lungs
what happens when inspiratory muscles relax (boyle’s law)
lung volume decreases, pressure in lungs increases, air is blown out of lungs (following pressure gradient, via bulk flow)
muscles used for ventilation at rest
external intercostals and diaphragm use at rest
(contracts, air flows in)
what other muscles are recruited during forceful breathing?
intercostals and abdominals
sternocleidomastoids and scalenes
what happens during quiet inspiration?
- diaphragm contracts and flattens
- muscles of inspiration contract and pull ribs up and out, sternum lifts up
–> thoracic and lung volumes increase
–> Pip and Palv decrease
–> Patm>Palv
–> air flows in
what happens during quiet expiration?
-diaphragm relaxes and moves upward
-muscles of inspiration relax, ribs and sternum “fall” back down
–> thoracic and lung volumes decrease
–> Pip and Palv increase
–> Palv>Patm
–> air flows out
what is the machine that measures changes in lung volume during ventilation?
spirometer
Total pulmonary ventilation (minute ventilation)= ?
ventilation rate (12 breaths/min) * tidal volume (500mL)= 6 L/min
the efficiency of breathing depends on both
rate and depth
how much air is moved into/out of the respiratory system per minute?
6L/min
(total pulmonary ventilation)
anatomical deadspace
150mL
because gas exchange does not occur in conducting pathways
what is a better indicator of ventilation efficiency?
alveolar ventilation
(the amount of air moves in and out the alveoli per minute)
alveolar ventilation=
ventilation rate* (Tidal volume- dead space volume)
= 12 breaths/min*(500-150mL)
= 4.2L/min
at the end of inspiration, the dead space (150mL) is filled with
fresh air
the first exhaled air comes out of the —–. Only —-mL leaves the alveoli.
dead space
350mL
at the end of expiration, the dead space is filled with
stale air from alveoli
end of expiration, inhale…
500mL of fresh air (tidal volume)
how is the 500mL of fresh air divided when inhaled?
-dead space (150mL) is filled w fresh air
-only 350 mL reaches alveoli
(the first 150mL of air into the alveoli is stale from the dead space)
