Pulmonary ventilation

Question 1

What factors does lung volumes and capacities depend on?

Answer 1

Lung volumes & capacities depend on factors like age, sex, height, as well
as lung properties (compliance, obstruction/damage due to disease)

Question 2

Refer to slides to lung volumes and capacities graph

Answer 2

Refer to slides to lung volumes and capacities graph

Question 3

What gradients does pulmonary ventilation maintain?

Answer 3

Pulmonary ventilation (movement of air from the atmosphere to
gas exchange surfaces within the lung) is required to maintain O2
and CO2 gradients between alveolar air and arterial blood.

Question 4

What does pulmonary ventilation enable?

Answer 4

This enables a sufficient level of gas exchange to take place,
ensuring adequate O2 supply/CO2 removal to/from respiring tissues
(via blood).

Question 5

What does adequate transport of O2 from atmosphere to respring tissues depend on?

Answer 5

Depends on:
-Healthy levels of alveolar ventilation
-Gas exchange
-Cardiac output

Question 6

What maintains the pressure gradients between alveoli and blood?

Answer 6

Pressure gradients between alveoli and blood
are maintained by adequate ventilation

Question 7

What effect does an increase in ventilation have on partial pressure gradient and therefore to gas exchange?

Answer 7

↑ventilation = ↑partial pressure gradient (between alveoli and blood) = ↑gas exchange

Question 8

What happens to partial pressure of O2 within alveoli during hyper and hypoventilation?

Answer 8

-Hypoventilation results in ↓ PAO2
-Hyperventilation results in ↑ PAO2

Question 9

What happens to partial pressure of CO2 within alveoli during hyper and hypoventilation?

Answer 9

-Hypoventilation results in ↑PACO2
-Hyperventilation results in ↓PACO2

Question 10

What is the equation for ventilaiton?

Answer 10

V=VT x f

-V is minute volume(mL), the total volume of air inhaled in all breath over one minute
-VT is tidal volume (mL), the volume of air inhaled in each breath
-f is the frequency(min-1), the number of breaths per minute

Question 11

Why is alveolar air not equal to the volume of inspired air?

Answer 11

o Gas exchange only takes place in alveoli, but air must first pass
through the airways (airways = “anatomic dead space”)
o The respiratory system is two-way system; air enters and leaves via
the same path. Also, a residual volume of air remains in the airway
& lungs at the end of expiration.
o This means that the final ≈150mL (dead space volume) of each
inspiration never reaches the alveoli or takes place in gas exchange.

Question 12

What is the equation for alveolar ventilation?

Answer 12

VA=(VT-VD) x f
-VA is Alveolar minute volume (mL), the toal volume of fresh air entering the alveoli across all breaths over one minute
-VT is tidal volume (mL)
-VD is dead space volume (mL), the volume of air remaining in the respiratory system at the end of expiration

Question 13

What does VT-VD equate to?

Answer 13

The volume of fresh air entering the alveoli in each breath

Question 14

How does the respiratory system
achieve movement of air?

Answer 14

Gases naturally move from (connected) areas of higher
pressure to lower pressure, until an equilibrium is re-
established.

Question 15

What is the equation for ideal gas law?

Answer 15

PV=nRT
P is Pressure
V is Volume
n is number of moles
R is gas constant
T is temperature

Question 16

What is boyles law?

Answer 16

P is direcrly proportional to n/v

-P is pressure so the number of gas molecules within a given volume
-If n remains constant, an increase in volume results in a decrease in pressure

Question 17

What occurs to pressure and lung volume during inspiration?

Answer 17

-Diaphragm contracts and thoracic cavity expands.
-Alveolar pressure decreases and lung volume increases

Question 18

What occurs to pressure and lung volume during expiration?

Answer 18

-Diaphragm relaxes (and lung recoils).
-Thoracic cavity volume decreases
-Alveolar pressure increase
-Lung volume decreases

Question 19

What happens to alveolar pressure during inspiration?

Answer 19

The outer surfaces of the lung are
pulled outwards (expansion).
↑volume = ↓alveolar pressure.
Palveoli < Patmosphere
Air flows from high (atmosphere) to
low (alveoli) pressure.

Question 20

What happens to alveolar pressure during expiration?

Answer 20

Air within the lung is compressed.
↓volume = ↑alveolar pressure.
Palveoli > Patmosphere
Air flows from high (alveoli) to low
(atmosphere) pressure.

Question 21

What happens to alveolar pressure at the end of expiration?

Answer 21

At the end of expiration,
Palveoli = Patmosphere, therefore
there is no movement of air

Question 22

What is the pleural cavity?

Answer 22

fluid filled space between the
membranes (pleura) that line the chest wall
and each lung

Question 23

What does the pleural cavity help to reduce?

Answer 23

helps to reduce friction between lungs and chest.

Question 24

What do the properties of the pleural cavity mean to the changes in volume and what does this result in?

Answer 24

The properties of the pleural cavity (sealed,
fluid-filled) mean that it resists changes in
volume. Thus, changes in the volume of the
thoracic cavity (due to resp. muscle activity)
result in changes in lung volume.

Question 25

What does the opposing elastic recoil of the chest wall and lungs result in?

Answer 25

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

Question 26

What is negatice pressure and what type of force does this generate?

Answer 26

lower number of molecules per volume
(relative to surroundings) → generates collapsing force (pulls
surfaces of contained space together).

Question 27

What is the positive pressure?

Answer 27

increased number of molecules per volume
(relative to surroundings) → generates expanding force (pushes
surfaces of contained space apart).

Question 28

What are the steps involved in the movement of air into the lungs during inspiration ?

Answer 28

Respiratory muscles (e.g. diaphragm)
contract
↓
Volume of thoracic cavity increases
↓
Intrapleural pressure becomes more negative
↓
Lungs expand, increasing volume
↓
PAlv (alveolar pressure) decreases below PAtm
(atmospheric pressure)
↓
Air moves down pressure gradient, through
airways into alveoli, expanding the lungs

Question 29

What are the steps involved in the movement of air into/out of the lungs during expiration ?

Answer 29

Respiratory muscles (e.g. diaphragm)
relax, lungs recoil due to elastic fibres
↓
Volume of thoracic cavity decreases
↓
Intrapleural pressure increases
↓
Lungs compressed*, volume decreases
↓
PAlv increases above PAtm
↓
Air moves down pressure gradient, into
atmosphere, deflating lungs

Question 30

What are the 4 steps in inspiration and expiration which link to:
1. Intrapleural pressure (Cm H20)
2. Alveolar pressure(cm H20)
3. Air flow(L/sec)
4. Volume change(liters)

Answer 30

1) As lung volume increases during inspiration,
intrapleural pressure becomes more negative
due to the elastic properties of the lung
generating increasing recoiling force.
2) As the lungs expand, the increase in volume
decreases PAlv. As air enters the lungs, the
pressure re-equilibrates once again as the
increased concentration of gas molecules
compensates for the increased volume (P = n/V)
3) When PAlv < PAtm the pressure gradient causes
air to move into the lungs. Where PAlv > PAtm air
moves out. The speed of airflow is dependent on
the pressure gradient and level of airway
resistance present.
4) Entry of air into the lungs due to (3) leads to
inflation and increased volume, which is
reversed during expiration.

Question 31

What does pneumothorax involve?

Answer 31

Pneumothorax involves entry of air into the pleural cavity, loss of negative intrapleural pressure, and collapse of lung tissue

Question 32

What happens if either pleural membrane is ruptured?

Answer 32

If either pleural membrane is ruptured, the
pressure gradient between the pleural cavity
and surrounding environment will cause air to
enter (pneumothorax) until intrapleural
pressure = atmospheric pressure.

Question 33

What does entry of air into pleural cavity result in?

Answer 33

Entry of air = ↑ pleural cavity volume (at the expense of the lung volume, which decreases).
Elastic recoil of lung tissue, and expansion of the chest during inspiration can then potentially draw further air into the pleural space.