Respiratory System - Topic 3

Question 1

What causes air to flow through the airways?

Answer 1

a pressure difference between two ends of the airway

Question 2

What are some important pressures?

Answer 2

1. atmospheric pressure, Patm (at nose or mouth)
   
   • typically 760 mmHg at sea level
2. alveolar pressure, Palv (within alveoli)
   
   • changes throughout breathing cycle to be more, less or equal to Patm
3. intrapleural pressure, Pip (within pleural cavity)
   
   • lower than Patm during normal, quiet breathing
   • functions like a vacuum to ‘pull’ the lungs open because the space has a negative pressure

Question 3

Air moves by ______ flow from a region of ______ pressure to _______ pressure

Answer 3

bulk; high; low

Question 4

When does air enter the lungs?

Answer 4

when Palv is less than Patm, air will enter the lungs

Question 5

Explain flow

Answer 5

• directly proportional to pressure difference and inversely proportional to airway resistance
• F = Palv - Patm/ R

Question 6

What causes changes in alveolar pressure?

Answer 6

changes in lung dimensions (volume); according to Boyle’s Law P1V1 = P2V2

• volume decreases, pressure increases and vice versa

Question 7

What are the important pressure relationships required for ventilation?

Answer 7

Palv - Patm is the driving pressure gradient for airflow into and out of the lungs => determines direction of airflow

Pip = pressure in intrapleural cavity => at rest, balance between tendency of lungs to collapse and tendency of chest wall to expand

Ptp = transpulmonary pressure => Palv - Pip
major determinant of lung size

Pcw = pressure across chest wall => Pip - Patm

Question 8

Pressures at the end of an unforced expiration (FRC)

Answer 8

Palv = Patm = no air flow

Ptp (Palv - Pip) exactly opposes elastic recoil of lung, lung volume remains stable

Pcw (Pip - Patm) is balanced by outward elastic recoil of chest wall

• Pip = Pcw