Ventilation and breathing mechanics

Question 1

Define ventilation

Answer 1

The movement of air in the atmosphere and the lungs so that gas exchange can occur in alveoli

Question 2

What is the purpose of ventilation?

Answer 2

To maintain pH between 7.35-7.45, by removal of CO2 and bringing in of air from atmosphere, enabling gas exchange

Question 3

How is the total pressure gradient generated?

Answer 3

It is generated by respiratory muscles, enabling gas to move down the pressure gradient. Movement occurs in bulk flow via conduction zone whereas in alveolar zone it occurs via diffusion

Question 4

Name the 4 types of respiratory muscles

Answer 4

1. diaphragm
2. intercostal muscles
3. abdominal muscles
4. accessory muscles

Question 5

Describe and explain the function of the diaphragm

Answer 5

The diaphragm is dome-shaped when relaxed, as it contracts it flattens and moves down. Consists of R & L hemidiaphragms. These contain holes for oesophagus BV’s, nerves & lymph
It divides the thorax from the abdomen, it is the major muscle involved in r/s
It can shorten by 40%, with a SA of 900cm2
spends 45% of its time contracting
unilateral & bilateral damage can occur and ventilation can still occur as other muscles compensate for damage
involved in inspiration

Question 6

Describe and explain function of intercostal muscles

Answer 6

There are 3 types: innermost, internal and external
External is the most used, involved in inspiration whereas internal are used in forced expiration, speech/singing
Internal & external run in opposite directions to each other
Found between the ribs, which have notches to protect BV’s, nerves & lymphs

Question 7

Describe and explain function of accessory muscles

Answer 7

These are involved in forced movements, e.g., exercise causing heavy breathing, singing etc
Resp patients use them most to aid in breathing
Made of 3 part scalene and sternocleidomastoid, involved in inspiration, sterno joins to clavicle and manubrium allows movement of head
Trapezius extends from base of skull down the back, enables chest to increase in size
Pec extend across chest to humerus, responsible for lifting chest
involved in inspiration

Question 8

Describe and explain function of abdominal muscles

Answer 8

Made of 4 muscles: internal & external obliques, rectus abdominals and transverse abs
internal- located under external, run in the opposite direction to external
external located on front/side of the abdomen
Rectus abdominals- ‘six-pack abs’, front abs
transverse- the deepest part of abs, wraps around the spine for protection & stability
involved in expiration

Question 9

Define and explain FRC?

Answer 9

Functional residual capacity, is a volume of gas that is always in the lungs at the end of a breath, healthy FRC is 2-3 litres
there is no pressure gradient at this point, Outward recoil of chest is balanced by inward recoil of lungs

Question 10

Mechanism of lungs during inspiration

Answer 10

1. air flows into the lungs down the pressure gradient
2. the thorax expands following contraction of inspiratory muscles
3. Alveolar pressure decreases as thorax volume increases (Boyle’s law)
4. Lungs stretch to fill & expand thorax further
5. pleural membrane becomes more negative

Question 11

Describe the function of type 1 pneumocytes

Answer 11

These are alveolar cells that line the alveolar surface. They are extremely thin and adapted to carry out gas exchange.

Question 12

Describe the function of type 2 pneumocytes

Answer 12

These are alveolar cells that secrete surfactant proteins to reduce surface tension. The surfactant creates a moist surface inside the alveoli to prevent the sides of the alveolus adhering to each other