Tension defined

the internal force generated by a structure

Law of laPlace states that for cylindrically shaped structures the formula is what?

T=Pr

T=wall tension

P= pressure of liquid in cylinder

r= radius

what does the law of LaPlace show or mean ( a lose definition)

as a structure expands its radius, wall tension increases

How is this law applied to real life?

Aortic aneurysms is more likely to rupture than a normal segment of the aorta b/c the radius is greater = increased wall tension

also capillary will withstand a pressure of 100mmHg better than a vein b/c capillary has a tiny radius compared to a vein

How does the law of LaPlace work with Spheres?

The ratio is doubled

2T=Pr

or (T= Pr/2)

how is LaPlaces law applied to real life in spheres

the LV, the greater the filling pressure, the greater the tension in the ventricular wall.

LaPlaces law in the alveoli

2T=Pr

or

P=2T/r

Laplaces law in the alveoli states that pressure needed to expand an alveolus is diresctly proprtional to__1__ and inversly proportional to __2__

1) surface tension

2) radius

P=2T/r

Alveoli are unique spheres b/c why?

they have H20 covered membrane

and water has surface tension

Alveoli act like bubbles and bubbles tend to pull toward what? and do what?

pull toward a smaller radius and collapse

the collapse of the alveoli is driven by what?

surface tension of H2O

van der Wall’s forces

what is the cumulative effects of cohesive intermolecular forces on the surface of a fluid at a liquid/gas or liquid/liquid interface

Surface tension

In the alveoli surface tension is _____ ____

wall tension

Law of Laplace explains what in the Alveoli

what would happen in the alveoli if not for surfactant

- smaller alveoli would empty into larger alveoli
- smaller alveolar spheres would be more difficult to expand than large alveoli

surfactant is composed of what?

dipalmityl phosphatidylcholine and Phospholipids (lecithin and spingomyelin) secreted by the alveolar (type II) cells

We all know that small alveoli are not harder to inflate compared to large alveoli. If this was true we wouldn’t have such well matched ventilation and perfusion ratios. thus we know that sufactant lowers __1__. and that small alveoli have more concentrated __2__ vs expanded (larger) alveoli and thus are easier to expand. so __3___ radius ___4___ surface tension by ___5___ surfactant concentrations

1) surface tension

2) surfactant

3) decreaseing

4) decreases

5) increasing

T=Pr example in Normal Alveoli

if r decreases, T decreases with P constant

- pressure in alveoli doesn’t change
- surfactant is the great equalizer
- explainds why small alveoli don’t empty into large alveoli in normal lungs

what cause the alveoli to collapse?

the water

without it they would stay open like a shopping bag

With adequate alveolar gas flow normal ventilatory to perfusion ration of _____ should be maintained

0.8

V/Q mismatch occurs with what?

inadequate flows

Alveolar Gas equation relates what to what?

PAO2 to FiO2

Formula for Aveolar Gas Equation

PAO2 = Fio2 x (Patm - PH2O) - PaCO2 / RQ PAO2= alveolar oxygen tension FiO2= inspired O2 concentration Patm= 760 mmHg PH20= 47 mmHg @ body temp PCO2= 25-45 mmHg RQ= respiratory quotient (normal 0.8)

What is the shorcut for estimating PaO2 from FiO2

FiO2 < 50% multiply FiO2 by 5

FiO2 > 50% multiply FiO2 by 6

the product is calculated PaO2

ex 0.21 x 5 = 105