Law of LaPlace Flashcards
How is tension defined?
the internal force generated by a structure
Law of LaPlace states that for cylindrically shaped structure
T=Pr
As a structure expands it’s radius….
wall tension increases
For blood pressure, wall tension is proportional to the radius. Example…
Aoritc Aneurysm is more likely to rupture than a normal segment because the radius is greater increasing wall tension.
Law of Laplace for sphere’s
T=Pr/2 or 2T=Pr or P=2T/r
tension is a factor of two due to the spherical area.
As the sphere expands its radius, the tension in the wall structure increases
tension is proportional to radius
Law of LaPlace for alveoli
2T=Pr of P=2T/r
P is the distending pressures within the alveolus. T= surface tension, R=radius of alveolus
This relationship shows that the pressure needed to expand an alveolus is 1) directly proportional to the surface tension, and 2) inversely proportional to the radius
What is important in keeping the alveoli open?
surface tension of water
What is the wall tension for the alveoli?
surface tension
What is surfactant?
dipalmityl phosphatidylcholine and phospholipids (lecithin and spinomyelin) secreted by the alveolar epitheliums’s great alveolar(type 2) cells
what are some effects of lack of surfactant?
ARDS and premies… glassy terminal bronchioles and terminal bronchiole constriction and alveolar collapse.
Do smaller alveoli have more or less surfactant?
MORE.
decreasing the radius decreases the surface tension by increasing the surfactant concentration.
In normal alveoli. ir R decreases and P is constant… what happens to T
T decreases
in ARDS if r decreases what happens to T and P?
T decreases with increased P requirements. Because of this.. the smaller alveoli empty into the alveoli with less tension and pressure requirements and cause atelectasis
estimate PaO2 from FiO2 < 50%
multiply FiO2 by 5, product is calculated PaO2
estimate PaO2 from FiO2 > 50%
Multiply FiO2 by 6, product is calculated PaO2
