Test 1-4: Law of Laplace & Surface Tension
With adequate alveolar gas flow, the normal ventilatory to perfusion rate (V/Q) should be maintained at _____
0.8 ratio
3 types of Atelectasis
1) Surfactant deficiency atelectasis 2) Compressive atelectasis 3) O2 diffusion atelectasis
Formula for Law of Laplace- Spherical Structures
2T = Pr or T=Pr/2 (2 x Wall Tension = Pressure of fluid in cylinder x radius)
Law of Laplace-Cardiac application
2T=Pr/H Chronic higher pressures cause thickened walls (hypertrophy) to balance equation greater pressue= greater tension
Estimating PaO2 from FiO2 if normal V/Q -FiO2 less than or equal to 50%, multiply FiO2 by _____ -FiO2 greater than 50%, multiply FiO2 by _____
5; 6
Compressive atelectasis
A force compresses the lungs and physically collapses the alveoli.
Alveoli charactersitics
Alveoli are unique spheres because they have a fluid (H2O) covered thin membrane Water has Surface Tension Alveoli act like bubbles and bubbles tend to pull toward a smaller radius and collapse THIS COLLAPSE IS DRIVEN BY SURFACE TENSION OF WATER Van der Waal's forces
Why is an aneurysm more likely to rupture than a normal section of vessel wall?
An increase in diameter thus and increase in wall tension
What will withstand 100mmHg of pressure better, a vein or a capillary? and why?
Capillary, because the radius is much smaller in a capillary than a vein thus a much smaller wall tension.
Surfactant deficiency Atelectasis
Decreased surfactant leads to the application of the Law of Laplace in alveoli and water surface tension causes small alveoli to collapse and empty into larger ones with lower pressures
Decreasing radius increases/decreases surface tension in the lungs by increasing surfactant concentration
Decreases
Tension is (directly/inversely) proportional to radius
Directly
Greater pressure = Greater/Less Tension
Greater
Alveoli with small radius will have a _____ pressure inflation requirements in ARDS
Higher
Applications of Laplace law-spheres ( T=Pr/2) in surfactant-deficient alveoli (ARDS)
If r decreases, P increases, no change in T because no surfactant to lower Tension. -Alveoli with a small radi have higher pressure inflation requirements and will empty into alveoli with lower pressures. -Explains why the above happens in patients with ARDS causing atelectasis.
Applications of Laplace law-spheres ( T=Pr/2) in normal alveoli
If r decreases, T decreases (d/t concentrating surfactant) with P constant. -Pressure in alveoli doesn't change. -Surfactant is the great equalizer -Explains why small alveoli don't empty into large alveoli in a normal lung.
As a structure expands (increasing radius) the wall tension will increase/decrease
Increase
Surfactant concentration _____ with decreasing size of alveoli
Increases
Paschals Principle
Pressure will equilibrate throughout
Alveolar gas equation
Relates PAO2 to FiO2 if all things are working well PAO2=FiO2x(Patm-PH2O)-PaCO2/RQ -PAO2=Alveolar oxygen tension -FiO2= Inspired oxygen concentration -Patm=760mm Hg -PH2O=47 mm Hg, saturated H2O vapor press. at body temp. -PCO2= 35-45 mm Hg -RQ= Respiratory quotient (resp. exchange ratio), normal 0.8(RQ = CO2 eliminated / O2 consumed)
Surface tension in the alveoli is lowered by _____
Surfactant
Law of Laplace explains what would happen in the alveoli if not for _________
Surfactant Without surfacant, smaller alveoli would collapse and empty into larger alveoli the smaller alveoli would also be more difficult to expand than larger alveoli without surfactant
Formula for Law of Laplace- Cylinders
T = Pr (Wall Tension = Pressure of fluid in cylinder x radius)
Surface Tension
The cumulative effects of cohesive intermolecular forces on the surface of a fluid at a liquid/gas or liquid/liquid interface IN ALVEOLI, SURFACE TENSION IS WALL TENSION
Tension
The internal force generated by a structure
Law of Laplace-Alveoli
The law of Laplace states 2T=Pr or P=2T/r P=distending pressures within the alveolus(dynes/cm2) T=surface tension of the alveolar fluid(dynes/cm), and r=radius of the alveolus(cm) 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.
O2 diffusion atelectasis
When enough oxygen has diffused through the alveoli the alveoli begins to shrink. With no other gasses to help hold it open (N) the alveoli collapse. A patients who has had all lung Nitrogen washed out and have 100% O2 in lungs is at risk.
Respiratory Distress Sydrome
caused by a lack of surfactant in newborns and is characterized by glassy appearing terminal bronchioles and alveoli due to lack of surfactant. Terminal bronchiole constriction and alveolar collapse ensues.
