Physio Ii: Respiratory Mechanics

Front 1

what are 2 ways that you can inflate lungs?

Back 1

blowing them up like a balloon
putting them in a space with negative pressure (pleural space)

Front 2

how do lungs remain inflated?

Back 2

because the pressue inside the lungs (which is the same at atmospheric pressure of the surrounding air) is greater than the pressure surrounding the lungs in the pleural space (subatmostpheric)

Front 3

what is the state of the lung in its natural state (in the thoarx) and how is its elastic recoil force acting?

Back 3

lung is inflated in natural state
elastic recoil acts to collapse the lung

Front 4

what is the state of the chest wall in its natural state? how does its elastic recoil forces act upon it?

Back 4

chest wall is collapsed normally
elastic recoil acts to expand it

Front 5

how do the opposing elastic recoil forces of the lung and chest wall affect the pleural space?

Back 5

gives the pleural space a negative pressure
(chest wall pulling out, lungs pulling in; like pulling 2 slides apart)

Front 6

what is the functional residual capacity? what defines it?

Back 6

it is the amt of gas in the lungs when the mouth is open and the mm. are relaxed
defined by the equilibrium pt where elastic recoil of lungs and chest wall are equal and opposite.

Front 7

what happens with a pneumothorax?

Back 7

the pleural pressure becomes positive relative the the pressue inside the lungs;
this collapses the lungs (Po>Pi) and the chest wall recoils (expands)

Front 8

how does lung elastic recoil arise?

Back 8

elastic recoil of the lung tissue polymers;
surface tension forces:water-lined alveoli tend to reduce size of surface

Front 9

what is the main contributor to lung recoil and how is this demonstrated?

Back 9

surface tension is main contributor
if fill lung with water, there is no air/water interface and therefore no surface tension...it is much easier to inflate lung with water because dont have to overcome surface tension. (curve shifts left)

Front 10

how does surfactant prevent the alveoli from collapsing?

Back 10

separates the water molecules and disrupts/decreases the surface tension.

Front 11

what would happen to alveoli of different size if there was no surfactant?

Back 11

LaPlace's Law: P~T/R
the smaller alveolus would have a higher pressure than the large alveolus and air would move from the small to the large, causing the small to collapse (perfusion w/o ventilation=shunt)and the large to overdilate

Front 12

how does surfactant stabilize alveoli of different sizes?

Back 12

each alveolus is exposed to the same amount of surfactant but the smaller alveolus has a higher concentration covering its surface and therefore a lower net surface tension. because the large alveolus has less surfactant on its surface it has a higher net surface tension. the difference in surface tension is enough to balance out the difference in radius and thus allows the 2 alveoli to remain at the same pressure even with different volumes. thus there is no flow of gas from one to the other.

Front 13

why is the pressure greater inside a smaller alveolus when there is NO surfactant?

Back 13

the water molecules exert forces on each other. the net force is downward, collapsing the alveolus. in a smaller alveolus, the inwardly directed force is larger.

Front 14

what is the main components of surfactant and where is it produced?

Back 14

produced by alveolar type 2 cells;
dipalmitoyl phosphatidyl choline (plus Ca2+, protein);
relatively insoluble in water (hydrophobic);

Front 15

what is the main sx in infant respiratory distress syndrome and why does this occur?

Back 15

main sx is difficulty breathing
seen in premies b/c surfactant is not produced until the last weeks in utero; w/o surfactant the lungs have a large recoil force and the force required to inflate the lungs may be greater than the infant can manage

Front 16

where is surfactant?

Back 16

on the surface of the alveolus

Front 17

which has a higher surface tension when there is surfactant present?

Back 17

the larger alveolus has a higher surface tension because the surfactant is less concentrated on its surface

Front 18

how do surface area and radius change as an alveolus is expanded?

Back 18

SA increases as a square of the radius
importance: if double radius, increase SA by 4 and decrease surfactant concentration by 1/4