The Work of Breathing

Question 1

Describe how we create a pressure gradient in the lungs

Answer 1

• gas will move from a high pressure to low pressure
• right before a breath, the pressure outside the body and inside the lungs are equal, no air is moving
• as you inhale, your diaphragm drops while you rib cage expands
• this increases the volume in your chest, which lowers the pressure
  Inhalation: volume increasing, pressure inside lungs dropping, so air rushes in
  Exhalation: volume is decreasing, pressure in lungs is increasing, air rushes out

Question 2

What are the two opposite forces that must be overcome to take a breath?

Answer 2

The stiffness of the lungs and the resistance of the airways to the lungs

Question 3

What is pulmonary fibrosis?

Answer 3

• thickening and scarring of the alveolar membranes
• can arise from chronic inflammation or exposure to industrial chemicals

Question 4

Describe the aspects of lung stiffness

Answer 4

Lung stiffness is related to compliance (C = change in V/ change in P)
Fluids surrounding the lungs exert surface tension:
- alveoli are lined with fluid that exert surface tension
- walls of alveoli are every thin, enhancing this effect
- must overcome surface tension to expand lungs

Question 5

Describe how the surfactant that the alevoli produce disrupts surface tension

Answer 5

• Relieves surface tension and allows the alveoli to expand during a breath
• failure to produce adequate surfactant results in difficulty in expanding the lungs and reduced oxygen intake
• premature infants don’t produce surfactant, resulting in respiratory distress syndrome (RDS)

Question 6

Describe airway resistance through the respiratory tract

Answer 6

• need to move air from outside to alveoli
• air is inducted though the bronchi and bronchioles
• exert force (friction) on the air that must be overcome
• a very small change in diameter of the lumen of the brionchi results in a very large change in resistance (like the lumen of blood vessels with the rule of 16)

Question 7

What are the two different types of issues with breathing?

Answer 7

Obstructive vs. restrictive

Obstructive: resistance to airflow (asthma or chronic bronchitis)

Restrictive: reduced lung capacity (reduced lung compliance or insufficient surfactant release)

Question 8

Describe the spirometry (pulmonary function) test

Answer 8

• A spirometer measures volume inspired/exhaled
• common, simple test
• can measure how much and how fast you breathe
• very useful for testing the response to therapy

Question 9

What breathing pattern is seen in the spirometry test?

Answer 9

• 2 normal breaths
• big exhalation
• normal breath
• big inhalation and then big exhalation
• two normal breaths

Question 10

What are the spirometry trace volumes and their definitions?

Answer 10

Tidal volume:
- volume of air moved in and out during a normal quiet breath
Inspiratory reserve volume:
- extra volume that can be inspired with maximal inhalation
Expiratory reserve volume:
- extra volume that can be exhaled with maximal effort
Residual volume:
- volume remaining in lungs after maximal exhalation
Minimal volume:
- volume remaining in lungs if they collapsed

Question 11

What are the spirometry trace capacities and their definitions?

Answer 11

Vital capacity:
- volume of air you can shift in and out of your lungs
Total lung capacity:
- total volume in lungs when you have filled them to max
Inspiratory capacity:
- total volume of air you can inspire from rest
Functional residual capacity:
- volume remaining in lungs after normal exhalation

Question 12

Describe the functional use of a spirometry test

Answer 12

You can find out the forced expiratory volume in one second (FEV1)
- ie. how much of the vital capacity (VC) comes out in first second
- reduced with diseases causing resistance to airflow (eg. asthma)

• FEV/VC ratio
  Normal is ~80%
  <0.70 indicates airway obstruction (obstructive issue)
• If normal but they are having breathing troubles still, this tells you it is a restrictive issue