Mechanics of Breathing

Question 1

What is the equation for flow?

Answer 1

Flow (V)= (Patm-Palveoli)/R

Question 2

Which muscle is the most important for inspiration?

Answer 2

Diaphragm

Question 3

Describe the movements of the diaphragm during inspiration.

Answer 3

Muscle fibers in the diaphragm radiate out from the central tendon and they shorten during inspiration ind pull it down in order to increase intrathoracic and intrapleural pressure

Question 4

What animal has active exhalation all of the time?

Answer 4

Horses

Question 5

What other muscles help during inspiration?

Answer 5

External intercostals-elevate ribs
Sternomastoids-raise sternum
Scalene-raise the first two ribs

Question 6

How is the lung able to move in the thoracic cavity?

Answer 6

The pleura that contains a small amount of pleural fluid allows it to slid up and down and the pressure in the intrapleural space determines alveolar volume and gas flow

Question 7

When do the nares tend to collapse and why?

Answer 7

The nares will collapse during inhalation due to a very high negative pressure

Question 8

What is laryngeal hemiplagia?

Answer 8

In horses, usually the left recurrent laryngeal nerve is damaged and the cricoarytenoids dorsalis is unable to open the glottis-roaring

Question 9

What is dynamic compress?

Answer 9

Little dogs have weak tracheas that collapse on inhalation and cause a honking noise

Question 10

What are some muscles of expiration?

Answer 10

• Abdominals- increase the pressure in the abdomen when the contract
• Internal intercostals-forces ribs downward

Question 11

What is a compliance curve?

Answer 11

This is when pressure and volume are plotted on a graph. Inspiration and expiration have a separate curve. Inspiration shows a greater increase of pressures at lower volume showing us that the lungs don’t work as well at TLC

Question 12

What are the basis for lung compliance?

Answer 12

1. Elastin and collagen
2. Surface tension
3. Interdependence

Question 13

How does surface tension increase the compliance?

Answer 13

Surfactant produced by alveolar type II cells, keep the alveoli from collapsing

Question 14

How does interdependence increase compliance?

Answer 14

If one region starts to collapse, the other areas around it create torsional pull that keeps it open

Question 15

Which region of the lung has higher ventilation?

Answer 15

Lower region

Question 16

Where is intrapleural pressure the most negative?

Answer 16

At the apex of the lung

Question 17

Why is the lower region of the lung more ventilated?

Answer 17

The IPP is so high at the apex it creates a higher negative pressure which expands the alveoli here more. This allows form more of the air to reach the lower alveoli to be used. The apical alveoli are much stiffer and therefore do not ventilate as much as the lower region.

Question 18

What happens during pneumothorax?

Answer 18

The intrapleural space and chest wall have been pierced. This cause the lung to recoil and the chest wall springs out and there is a negative IPP

Question 19

What happens to the lungs with emphysema?

Answer 19

The lung compliance in increased due to holes in the parenchyma. This gives it a very low recoil and the IPP is less negative. Patients often appear barrel chested and are unable to force the air out of the lungs without collapse of the airways

Question 20

What happens to the lungs with pulmonary fibrosis?

Answer 20

You get a decrease in compliance and an increased recoil due to build up in scar tissue. This creates a very negative IPP and the lung wants to collapse.

Question 21

Which airways have the most resistance?

Answer 21

Larger airways

Question 22

Why is the resistance in the alveoli so low?

Answer 22

The cross sectional area of the alveoli is so much higher than that of the large airways thus leading it to have a lower resistance

Question 23

Describe the flow of expiration on a compliance graph.

Answer 23

The graph will be asymmetric. The first part of expiration will be a sharp linear line in flow due to the recoil of the lungs and the large size of the airways having less resistance. This is called effort independence. Once the expiratory muscles start to act, this increases the alveolar driving forces and raises intrathoracic pressure. This will increase the resistance of the airways and collapse in unsupported ones and the flow of air being expired slows down from the fast flow when there was no effort