Lecture 19- mechanics of breathing

Question 1

What is pulmonary ventilation?

Answer 1

The exchange of air between the atmosphere and the alveoli of the lungs

Question 2

What is the value for intrapleural pressure at rest at sea level?

Answer 2

At rest it’s -4 mmHg. Pressure at sea level is 760 mmHg so it would be 756 mmHg

Question 3

How does intrapleural pressure compare to atmospheric and intrapulmonary pressure?

Answer 3

Always lower than atmospheric and intrapulmonary pressure

Question 4

What is a pneumothorax? What causes it?

Answer 4

An accumulation of air or gas in the pleural cavity caused by a disease or injury. eg. puncture wound to the chest.

Question 5

What affect does a pneumothorax have on pressure?

Answer 5

Loss of negative intrapleural pressure. Becomes close to 760 mmHg. The lung collapses

Question 6

What is lung compliance?

Answer 6

The ease with which the lung can be expanded

Question 7

What causes changes in lung compliance?

Answer 7

1. Over production fo fibrotic tissue = less elasticity
2. Change in mobility of chest wall- e.g. osteoporosis
3. Surface tension- the amount of surfactant produces will affect this.

Question 8

When we breath in what happes to intrapleural pressure?

Answer 8

It becomes even more negative. down to -6 from -4 mmHg

Question 9

How do you diagnose a pneumothorax?

Answer 9

insert needle then tube between lower ribs, air will rush out

Question 10

Which factors oppose inspiration and expiration?

Answer 10

1. Elastic recoil opposes inspiration
2. Aireay resistance opposes both

Question 11

What causes surface tension? Why does this limit compliance?

Answer 11

Intermolecular forces between moleculaes in a liquid.

The air-fluid interface surface of fluid is under tension- like a thin membrane being stretched. Limits the ability for it to expand. (thin fluid layer between alveoli and air.

Question 12

What is Laplace’s law?

Answer 12

**P= 2T/r. **

P=pressure

T=surface tenion

r= radius of alveoli

So smaller alveoli are harder to inflate, require more pressure

Question 13

Where is surfactant secreted? What does it do?

Answer 13

Type II alveolar cells.

Mixture of phospholipids that interact with the surface water, disrupting the cohesive forces in H20. Much less surface tension.

Question 14

What is respiratory distress syndrome and what is it caused by?

Answer 14

Lack of surfactant secretion in premature babies. Causes reduced compliance. Risk of alveoli collapsing. Difficult to inflate the lungs.

Question 15

What determines airway resistance?

Answer 15

Mainly determined by airway radius

Question 16

Describe and explain how resistance changes as you go down the brachial tree to the smaller airways?

Answer 16

Although the radius is greatly reduced going through th bronchial tree, there aare many of the airways so resistance is reduced. (less redistance than expected)

Question 17

Which factors affect airway resistance?

Answer 17

1. Lung volume- bronchi dilate as lungs expand
2. Bronchial smooth muscle- stimulation from parasympathetic nerves. Bronchoconstriction

Question 18

Which stimuli cause reflex bronchoconstriction?

Answer 18

1. reduced CO2, increased O2, to not overtake O2, to maintain plasma pH
2. Smoke, irritants
3. Histamine (e.g. allergic response)