Physiological Consequences of Disruption or Destruction of the Alveolar Capillary Membrane

Question 1

What is the alveolar-capillary membrane composed of?

Answer 1

• layer of surfactant
• type 1 alveolar cell
• basement membrane (shared between A & C)
• vascular endothelial cell

Question 2

What are the features of the A-C membrane?

Answer 2

• thing (0.5 microns)
• large surface area (50-100m²)
• alveolar vlolume 3-6L
• capillary volume 80mL (greater if +CO)

Question 3

Pneumonia refers to

Answer 3

an infection of the A-C membrane

Question 4

What are the physiological effects of disrupting the A-C membrane?

Answer 4

• abnormal gas exchange
• abnormal lung mechanics
• pulmonary vascular complications

Question 5

high PaCO2 occurs only by

Answer 5

inadequate ventilation (V_A)

Question 6

Low PaO2 occurs by

Answer 6

poor perfusion or low ventilation (type 1 and type 2 respiratory failure)

Question 7

Conditions that affect the A-C membrane result in

Answer 7

decreased compliance, stiffer lungs

Question 8

What is unique about emphysema with regards to the A-C membrane?

Answer 8

in emphyysema, there is less stiffness and increased compliance

tf path is more realated to obstruction it causes

Question 9

What are the mechanical effects of restrictive lung diseases?

Answer 9

• breathlessness
• increased WOB (especially on exercise)
• reduced lung volumes (all; TLC, RV, FRC, VC, FEV1)
  
  • stiff lungs favour collapse and pull the chest wall in
    
    • exception is emhpysema; +FRC due to +compliance
• altered pattern of breathing - small breaths at a fast rate
• reduced maximum ventilation

Question 10

In restrictive lung disease, the WOB is increased by

Answer 10

increased load

Question 11

In restrictive lung disease, the increased load is the

Answer 11

increased elastsic work of breathing

Question 12

What are the consequences of increased elastic WOB in restrictive lung disease?

Answer 12

• recruitment of accessory muscles (scalene, SCM) to generate higher pressures
• increased O2 consumption by these muscles
• risk of muscle fatigue if obstruction is severe

Question 13

What is the hallmark of restrictive lung disease on spirometry?

Answer 13

reduced forced vital capacity (FVC)

reduced FEV1 proportional to reduced VC

tf FEV1/FVC is normal

Question 14

In restrictive lung disease, the FEV1/FVC ratio is

Answer 14

normal

Question 15

In obstructive lung disease, the FEV1/FVC ratio is

Answer 15

low

Question 16

If a patient presents with low VC and a low FEV1/FVC ratio

Answer 16

restrictive and obstrictive defects are present

Question 17

In restrictive lung disease, compliance of the lungs is reduced by

Answer 17

• excess tissue composition (fibrosis, inflammation, malignancy, infection)
• surface tension in the alveoli

Question 18

In pulmonary fibrosis, the pressure-volume curve is shifted

Answer 18

to the right

i.e. need a lot of pressure to change volume of the lung

Question 19

In emphysema, the pressure-volume curve is shifted

Answer 19

to the left

i.e. loss of elastic tissue and loss of A-C membrane results in lungs like air filled sacks, requiring very little change in pressure to increase volume

Question 20

compliance =

Answer 20

change in V/change in P

Question 21

Maximum ventilation is

Answer 21

~35 x FEV1