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Flashcards in Pulmonary Mechanics Deck (18):

4 most important muscles of inspiration?

External intercostals. (first two are most important)


How are the external intercostal muscles such that they augment inspiration?

They slant downward and anteriorly, such that contraction will elevate the ribs, increasing the anteroposterior diameter of the chest cavity.


How does the length-tension curve vary between the diaphragm and other skeletal muscle?

The diaphragm has greater tension at greater lengths (curve shifted to right).
So... more air in lungs -> less tension generated by diaphragm.


What does Laplace's law have to do with the diaphragm?

Laplace's Law: Collapsing pressure of a sphere is inversely proportional to the radius. (recall, this is important for alveoli/ surfactant, too)
A diaphragm that's distorted such that it's flattened and the radius is larger will be unable to generate as much pressure.


What's a disease in which Laplace's Law plays a role in pathophysiology?

In emphysema, excess air is retained -> flattening the diaphragm.
The flattened diaphragm will be unable to generated as much force for inspiration. (and may actually just cause the rib diameter to decrease)


What can be measured clinically to approximate intrapleural pressure?

Esophageal pressure.


What 2 pressures contribute to alveolar pressure?
Why do you care about alveolar pressure?

Pleural pressure + alveolar elastic pressure.

Airflow in and out of lungs is determined by the difference between alveolar pressure and airway/atmospheric pressure.


In what situation(s) is pleural pressure positive?

Really only during forced expiration.
(During inspiration, it's very negative. During normal expiration it's less negative, such that elastic pressures overcome it.)


What is the Equation of the Motion of the Lung for total "pressure across the respiratory system"? (it has 3 components, 6 variables)

Total P = (E * V) + (R * Vdot) + (I * Vdotdot)

E = elastance. V = lung volume.
R = resistance. Vdot = airflow.
I = air inertance. Vdotdot = air acceleration.
(each "dot" represents a derivative)


How is static lung compliance defined?
How is related to elastance?

Static lung compliance (Cst) = delta lung volume / delta distending pressure.

Elastance (E) = 1 / Cst


What a disease with increased compliance?
With decreased compliance?

Increased: Emphysema.
Decreased: Interstitial fibrosis.


What's the important part of Poiseuille's Law?

Airflow velocity (Vdot) is proportional to radius^4.

(assuming laminar flow, which doesn't really happen)


Is airway resistance greater in the trachea/bronchi or in terminal bronchioles?

Resistance is greater higher up.
Analogous to the circulatory system, further on the tubes are smaller, but the total cross-sectional area is greater.


Airway resistance vs. lung volume?

Greater lung volume, less resistance.
The tubes open up.


What is the equal pressure point, and what the heck is a Starling resistor?

So... during expiration, pleural pressure will increase... such that somewhere in the airway, pressure inside will equal pleural pressure.
This can cause the airway to collapse partially, increasing resistance and creating a "Starling resistor."


Starling resistors happen more at low lung volumes and in more distal, collapsible structures.



Work of breathing is equally, mathematically, to....

W = integral ( P deltaV)

P = pressure, V = lung volume


Of the two variables, pressure and lung volume, which is changed to create increased work of breathing in disease of reduced compliance?

Increased pressure will lead to increased work.... and this has a linear pressure vs. volume curve that gets integrated.
(See slide 63)
With increased airway resistance, the curve that gets integrated to increase work... looks different. (see slide 64.. it's not linear)