Mechanics Of Lung & Chest

Question 1

How is lung compliance measured?

Answer 1

C = 🔼V/🔼P

C=1/E

Question 2

Explain hysteresis

Answer 2

The pressure/volume relationship differs depending on inflation or deflation

Shape due to forces needed to overcome:

1. Airway resistance
2. Frictional forces
3. Inertia of air+ tissues
4. Elasticity of lungs

Question 3

How does alveolar surface tension affect lung compliance?

Answer 3

Alveolar surface tension affects lung compliance.

Inflating lungs with saline instead of air eliminates surface tension. Two pressure-volume curves for lungs inflated to the same volume are shown, first with air and then with saline. The differences in the two curves occur because surface tension contributes significantly to lung compliance in the air-filled lungs. When lungs are inflated and deflated with saline, the lungs are more distensible, with a concomitant increase in lung compliance.

Question 4

What is rage purpose of saline’s in lungs?

Answer 4

Of lung is filled with saline so that

There is no surface tension

Hysteresis is not appearent

The inflation-deflation hysteresis is due to surface tension

Question 5

explain his surface tension is developed?

Answer 5

Intermolecular forces of attraction- in bulk a molecule is exposed to these forces from all around

Property of the surface of a liquid that allows it to act as an elastic sheet

Force per unit length/energy per unit area

Molecules at surface are only attracted from below and with each other

As a result, the surface of a liquid acts as an elastic sheet

Measured as Force per unit length or energy per unit area

Smallest surface area for a given volume is a sphere

Question 6

How does Laplace’s law apply to surface tension of soap?

Answer 6

Surface tension forms a sphere, and a pressure is developed inside the bubble

Laplaces’s law

T surface tension, r radius

P=4T/r

Increase in radius causes a decrease in pressure and vice versa

Note 4T is used when 2 surfaces as in a bubble, 2T if 1 surface as in alveoli

Question 7

How does alveoli size correlate to pressure?

Answer 7

Small alveoli develop a large pressure

Large alveoli develop a smaller pressure

Forms a pressure gradient

So, air would flow from the smaller to larger alveoli

Tendency would be for small alveoli to collapse and large alveoli to fill

Whole regions of lung may also remain collapsed after expansion

If it were not for surfactant!

Question 8

What is surfactant?

Answer 8

Surface active agent

Pulmonary surfactant - lipoprotein rich in phospholipid

Secreted by type II cells in the alveolus

Hydrophobic and hydrophilic regions

Main component is diapalmitoyl phosphatidylcholine (DPPC)

• reduces surface tension greatly-increasing lung compliance
• Effects are concentration (surface density) dependent - therefore as alveoli shrink-the effective concentration increases and surface tension falls

Question 9

What is the percentage phospholipids in surfactant?

Answer 9

90%

Question 10

What is the function of phospholipids in surfactant?

Answer 10

60% of which phosphatidylcholine (50% of which is DPPC)

7-15% phosphatidylglycerol

Reminder: phosphatidylinositol, phosphatidylserine, sphingomyelin, phosphatidylethanolamine, cholesterol

Question 11

What percentage of surfactant are proteins?

Answer 11

10%

Question 12

What is the functions of proteins in surfactant?

Answer 12

SP-A— large hydrophilic collagen-like lectin superfamily (collectins)-lung defense

SP-B— Hydrophobic -facilitates surfactant monolayer formation

SP-C —hydrophobic -facilitates surfactant monolayer formation

SP-D — large hydrophilic collagen-like lectin superfamily (collectins)- lung defense

Question 13

Explain functioning of surfactant

Answer 13

Surfactant promotes alveolar stability at low lung volumes. If surface tension remains constant (50 dyne/cm), alveoli that are interconnected but differ in diameter become unstable and cannot coexist. Pressure in the smaller alveolus is greater than that in the larger alveolus, which causes air from from the smaller alveolus to empty into the larger alveolus. At low lung volumes, the smaller alveoli tend to collapse , a phenomenon known as Atelectasis. Surfactant lowers surface tension proportionately more in the smaller alveolus. As s result, pressures in the two alveoli are equal , and alveoli of different diameters can coexist

Question 14

What is the biophysical mechanism of lung surfactant ?

Answer 14

Biophysical mechanism of lung surfactant for lowering alveolar surface tension. Surfactant molecules are compressed during lung deflation. At stage 3, surfactant molecules form micelles And are removed from the surface. On lung inflation, new surfactant is spread onto the surface film (stage 4).

Turnover of lung surfactant is high because of continual replacement of surfactant during lung expansion

Question 15

Why is surface tension necessary in hyper inflated states?

Answer 15

At hyperinflatedstates, surface tension is on3 of the forces necessary to make sure lungs would not pop out. At this point surfactantcannot counter the surface tension forces because the molecules are sparsely spread out.

At residual volume-deflated state, the surfactant spread density increases. It is essential now to counter surface tension forces to make sure the a”velocity are not completely deflated

Question 16

When does static compliance change?

Answer 16

In disease states

1. High compliance- lung inflates easily and has little elastic recoil, typical of Emohysema/COPD
2. Low compliance -lung inflates with difficulty due to large elastic recoil

Typical of pulmonary fibrosis, respiratory distress syndrome

Question 17

What 8s unique about obstructive and restrictive diseases?

Answer 17

Alter lung compliance. Patients with a chronic obstructive lung disease, such as emphysema, have abnormally high lung compliance. Patients with restrictive diseases, such as respiratory distress syndrome, have abnormally low lung compliance

Question 18

What is functional residual capacity(FRC)?

Answer 18

Volume of the lung at rest between breaths

No net recoil

Question 19

How do passive recoil forces set FRC?

Answer 19

-FRC is the lung volume at which the inwardly directed lung recoil is exactly balanced by the outwardly directed chest wall recoil - and the sum of the passive recoil forces is zero

Meaning- the volume of the lung when there is no active muscle input

Sets ventilatory tone

Question 20

What is dynamic compliance?

Answer 20

Because airway resistance increases the time for air to flow in to or out of the lung, as the frequency of breathing increases then the DV experienced by the lung falls

I.e., the respiratory muscles are expiring before the lung volume has increased maximally because flowbinto the lung volume has increased maximally because flow into the lung

The effect is reduced tidal volume with increasing frequency of breathing

In normal patients the frequency effect is not appearent since air flow is so quick

But in asthma-where high muscle tone in the airways produces high airway resistance-the tidal volume is reduced even modest increases in frequency

Dynamic compliance falls as airway resistance increases