Pulmonary Ventilation

Question 1

How is Total Ventilation calculated?

Answer 1

V = Vt x f

V - minute volume mL - total volume of air inhaled in one minute
Vt - tidal volume mL - volume of air inhaled in each breath
f - frequency min-1 - number of breaths per minute

Question 2

How are pressure gradients between the alveoli and blood maintained?

Answer 2

Through adequate ventilation.

Partial pressure within the alveoli increases as ventilation increases.

Question 3

How is Alveolar Ventilation calculated?

Answer 3

Va = (Vt -Vd) x f

Va - alveolar minute volume mL - the total volume of fresh air entering the alveoli across all breaths over one minute
Vt - tidal volume mL
Vd - Dead space volume mL - the volume of air remaining in the respiratory system at the end of expiration
Vt-Vd = the volume of fresh air entering the alveoli in each breath

Question 4

What is dead space volume?

Answer 4

The volume of ventilated air that does not participate in gas exchange.

Question 5

How does the respiratory system function to move air between the atmosphere and the alveoli?

Answer 5

Gases naturally move from an area of high pressure to an area of low pressure until an equilibrium is established.
Changes in lung volume induce changes in alveolar pressure. This generates pressure gradients between alveoli and the atmosphere thus causing air to flow.

Question 6

What is the pleural cavity?

Answer 6

A fluid-filled space between the pleura that line the chest wall and each lung. It helps to reduce friction between the chest wall and lungs

Question 7

The pleural cavity is sealed and fluid-filled, what does this mean in terms of function?

Answer 7

It means it can resist changes in volume. Therefore only changes in thoracic cavity volume can induce changes in lung volume.

Question 8

Why is intrapleural pressure negative?

Answer 8

The pleural cavity opposes the elastic recoil of the chest wall and lungs.
During inspiration, the intrapleural pressure becomes more negative.
During expiration, the intrapleural pressure increases.

Question 9

What occurs during inspiration?

Answer 9

1. Respiratory muscles contract e.g. diaphragm becomes flat
2. Thoracic cavity volume increases
3. Intrapleural pressure becomes more negative
4. Lungs expand, increasing volume
5. Alveolar pressure < atmospheric pressure
6. Air moves down pressure gradient, through airways into alveoli, expanding the lungs

Question 10

What occurs during expiration?

Answer 10

1. Respiratory muscles relax e.g. diaphragm becomes dome-shaped
2. Thoracic cavity volume decreases
3. Intrapleural pressure increases
4. Lungs compressed (forced exp only, in quiet breathing elastic recoil, is sufficient), volume decreases
5. Alveolar pressure > atmospheric pressure
6. Air moves down a pressure gradient, through airways into the atmosphere, deflating the lungs

Question 11

What is Pneumothorax?

Answer 11

Collapsed lung

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