Pulmonary Ventilation

Question 1

Define residual volume

Answer 1

The volume of air remaining in the lungs after a maximum forced expiration

Question 2

Define vital capacity

Answer 2

The total volume of air an individual is able to breath in going from a maximum forced expiration to a max forced inspiration

Question 3

Define total lung capacity

Answer 3

The volume of air within the lungs at the end of maximum inspiration

Question 4

Define inspiratory reserve volume

Answer 4

The additional volume of air that can be inspired at the end of a resting inspiration

Question 5

Define tidal volume

Answer 5

The volume of air inspired/expired at rest during quiet/normal breathing pattern

Question 6

Define expiratory reserve volume

Answer 6

The additional volume of air that can be expired at the end of a resting expiration

Question 7

Define functional residual volume

Answer 7

The volume of air within the lungs at the end of a resting expiration

Question 8

What is pulmonary ventilation

Answer 8

Pulmonary ventilation is the movement of air from the atmosphere to gas exchange surfaces within the lungs

Question 9

What is the importance of pulmonary ventilation

Answer 9

• Required to maintain adequate oxygen supply and carbon dioxide removal from respiring tissues
• Maintains gradients of oxygen and carbon dioxide between alveolar air and arterial blood
• This enables sufficient level of gas exchange to take place ensuring adequate supply and waste removal to and from respiring tissues

Question 10

What is ventilation dependent on

Answer 10

Ventilation depends on the volume (depth) and rate of breathing

Question 11

State the equation for finding the minute volume (include definition of components)

Answer 11

Minute volume (total volume of air inhaled in all breaths over one minute) =

Vt (tidal volume (ml) - (volume of air inhaled in each breath) x f (frequency (min-1) - the number of breaths per minute)

V = Vt x f

Question 12

Explain why the alveolar air is not the same as the air inspired

Answer 12

• The lungs contain a mixture of ‘fresh’ (air that has just entered the respiratory system) and ‘stale’ (residual air from the previous breath) air
• Gas exchange takes place in the alveoli but air must first pass through the airways ‘anatomic dead space’
• The respiratory system is a two way system - air enters and leaves via the same path and there is a residual volume of air that remains in the airways/lungs at the end of expiration
• This means that the final ‘dead space volume’ (around 150ml in an adult) of each inspiration never reaches the alveoli or takes part in gas exchange

Question 13

State the equation for alveolar minute volume and include definitions of all included components

Answer 13

Alveolar minute volume (ml) (the total volume of fresh air entering alveoli across all breaths in one minute =

Va = (Vt - Vd) x f

Vt = tidal volume (ml)
Vd = dead space volume - the volume of air remaining in the respiratory system at the end of expiration
F = frequency (min-1)
Vt - Vd = the volume of fresh air entering the alveoli in each breath

Question 14

State boyles law and how it is relevant to pulmonary ventilation

Answer 14

• Pressure is proportional to the number of molecules/the volume
• Hence, if the no of molecules stays constant as volume increases pressure will decrease

Question 15

Describe the process of inspiration

Answer 15

• The diaphragm moves down and flattens
• The external intercostal muscles contract
• The thoracic volume increases which decreases the intrapleural pressure to become more negative and decreases pressure inside the lungs
• The negative pressure created means that the pleural membranes are pulled closer together aiding the expansion of the lungs - the intrapleural pressure force must be greater than the force generated by the elastic recoil of the lung for expansion to occur
• When the pressure has decreased below the atmospheric pressure air moves down a pressure gradient and into the lungs

Question 16

Describe the process of expiration

Answer 16

• The diaphragm moves up and curves
• The external intercostal muscles relax
• The thoracic volume decreases which increases the intrapleural pressure to become more positive and so pressure in the lungs increases
• The positive pressure created means there is an expanding force so the surfaces of the pleural membranes are pushed apart aiding in the reducing of the volume of the lungs - reduced volume occurs when the pressure can no longer generate sufficient force to overcome the elastic recoil of the lungs
• When pressure increases above atmospheric pressure air moves down a pressure gradient and out of the lungs

Question 17

Describe the pleural cavity and why it is important in ventilation

Answer 17

• It is a fluid filled space between the membranes (pleura) that line the chest wall and each lung - helps to reduce friction between the lungs and the chest
• The properties of the pleural cavity (the fact it is sealed and fluid filled) means it can resist changes in volume
• This is why changes in the volume of the thoracic cavity result in changes in the volume of the lungs

Question 18

Why is the pressure in the pleural cavity subatmospheric

Answer 18

The opposing elastic recoil of the chest wall (outward) and lungs (inward) results in pressure within pleural cavity being sub atmospheric (under negative pressure)

Question 19

State and describe the two types of pressure including the forces they produce

Answer 19

• Negative pressure - there is a lower number of molecules per volume relative to the surroundings - causes a collapsing force so surfaces of the contained space are pulled together
• Positive pressure - increased number of molecules per volume relative to the surroundings - generates an expanding force so surfaces of the contained space are pushed apart

Question 20

State what an open and closed pneumothorax is

Answer 20

• Open pneumothorax - chest wall pleura (parietal pleura) is ruptured
• Closed pneumothorax - pleural membrane of lungs (visceral pleura) is ruptured

Question 21

Describe what happens during pneumothorax

Answer 21

• Pneumothorax causes affected parts of the lung to collapse due to elastic recoil
• Both mean that the pleural cavity is no longer sealed
• Means that air can move from the atmosphere into the pleural cavity via an open pneumothorax or air can move from the lungs into the pleural cavity via a closed pneumothorax
• Because the pleural cavity is subatmospheric air will move into it until the intrapleural pressure = the atmospheric pressure
• There is then no longer a negative pressure so lungs recoil to a small volume as the pleural cavity volume has increased