Surface Tension/Airway Resistance

Question 1

Surface tension is defined as the ___________(favorable or unfavorable) interactions between water and water and the _______________ (favorable or unfavorable)interactions between air-water

Answer 1

Favorable, unfavorable.

Question 2

Which of the following shows a favorable state for surface tension?

Answer 2

ANSWER Surface tension causes the alveoli to collapse. The smaller the alveoli, the more favorable it is for ST.

Question 3

What are the 3 effects of surface tension on the lungs?

Answer 3

1. Decreased Lung compliance
2. Water accumulation in lung (Allows for more h2o-h2o interactions)
3. Collapses small alveoli

Question 4

Assuming that surface tension in both alveoli are equal, which way will air flow? Why?

Answer 4

Flow from Small–> Big

This is due to LaPlace’s Law that states:
P=2T/r

Notice that if the Tensions are equal, then a smaller radius will generate a larger Pressure for a given alveoli. This higher pressure will cause air to flow from small–> big.

Question 5

Why does surfactant help prevent alveolar collapse?

Answer 5

Surfactant has polar and non polar ends. This allows it to interact with both water and air and decrease the surface tension.

Question 6

Babies that are born premature often have difficulty breathing (respiratory distress syndrome). What is the mechinsim of this syndrome?

Answer 6

Premature babies have not produced enough surfactant yet. Thus babies have the side effects of increased surface tension. Do you remember them?

1. Dec Compliance
2. Inc H20 In lungs
3. Alveolar collapse

Question 7

What are the 2 main variables that affect air flow during inspiration?

Answer 7

1. Compliance
2. Airway Resistance

Question 8

What is the most important factor that determines resistance in the pulmonary airways?

Answer 8

RADIUS

R~ 1/r⁴

Question 9

How does Air flow relate to Ohms law?

Answer 9

V=IR

delta P= Flow x R

V is synonymous with Pressure (P)

I is synonymous with Flow

R is still resistance

Question 10

1. Which chemical factors (neurotransmiters, signaling molecules etc) would cause an increase in airway resistance?
2. Which chemical factors (neurotransmiters, signaling molecules etc) would cause an decrease in airway resistance?

Answer 10

1. Bronchoconstrictors

1. Parasympathetic NS. (Acetylcholine)
2. Histamine (think of taking benadryl, an antihistamine, during allergic reactions where you are wheezing.

2. Bronchodilators

1. Sympathetic NS (epi/norepi which act on Beta Adrenergic Receptors- think of fight or flight. You want more O2 when youre running from a bear)
2. Beta adrenergic receptor agonists (albuterol)
3. CO₂ in bronchioles (signals your body to dilate to get more O₂

Question 11

An increase in Lung Volume results in an ________(inc.dec) in resistance.

How does this relate to people with Obstructive diseases?

Answer 11

Inc Lung Volume = Dec lung resistance

People with Obstructive lung diseases tend to breathe at higher Lung volumes. This HELPS with resistance but is deleterious for muscle forces needed to inflate lungs

Question 12

When does dynamic ariway collapse happen?

Answer 12

When the P_IP (intraplerual pulmonary pressure) is positive.

Examples:

• Forced Exhalation in healthy individual
• Ephysema during quiet expiration (due to decreased elastic recoil pressure and inc expiratory muscle use)

Question 13

What are 3 factors that cause lung dysfunction in Emphysema?

Answer 13

1. Reduced Pressure Gradient for outward airflow during expiration.
2. Chest Wall Forces collapse airways during expiration
3. Reduced integrity of bronchiole walls increases collapse of airways.

Question 14

Why does exhaling throuhg pursed lips help pts with emphysema breathe?

Answer 14

It increases airway pressures (P_AW) and helps reduce the probability of airway collapse.