Ventilation and Perfusion Flashcards
What is the difference between the conducting zone and respiratory zone?
- CONDUCTING - Involved in bulk movement of air into deeper tissue. Air not involved in gas exchange
- RESPIRATORY - where gas exchange occurs
What is anatomical dead space?
- Air breathed out unchanged from the conducting zone
Describe intrapleural pressure.
- Chest wall fixed at rest
- Lung parenchyma - tendency to recoil
- Pleural cavity - negative pressure relative to intrapulmonary pressure
- Keeps lungs attached to chest wall
What is the effect of puncturing of the chest on intrapleural pressure?
- Equates with atmospheric pressure
- Lung collapses
At rest, what is the relationship between alveolar and atmospheric pressure?
- Equal
- 0 cm H2O
What are the effects of gravity on the lungs when upright? PART 1
- Lungs sit low in pleural cavity
- Pressure gradient within this cavity
- More negative intrapleural pressure at top of cavity compared to bottom
What are the effects of gravity on the lungs when upright? PART 2
- Alveoli at apex of lungs - larger due to pull from rest of lung
- Alveoli at bottom - smaller. Compressed by weight of upper lung
Describe blood flow in the three zones of the lung.
- MIDDLE - stable flow
- TOP - reduced blood flow - act against gravity
- BASE - greatest amount of blood flow
Describe ventilation at the top of the lung.
- Alveoli at top of lung stretched so not compliant.
- No further stretching during inspiration
- Cannot decrease intra-alveolar pressure much
- Ventilation at apex of lung is low
Describe ventilation across the base of the lung.
- Smaller alveoli at rest
- More compliant and greater capacity for stretching
- Base of lung is larger - contains more alveoli
- Greater ventilation
What is ventilation and perfusion matching and what would it be in an ideal scenario?
- Matching of ventilation rate with blood flow
- For every unit of air in alveoli, would want the same number of carrying units in blood.
- V/Q = 1
Why does V/Q not equal 1 in all regions of the lung and what does it equal in the zones of the lung?
- Due to differences in ventilation and perfusion
- Apex of lung - V/Q = 3.3 (greater ventilation than perfusion)
- Base - V/Q = 0.63. Middle - V/Q = 1
- Base of lung - greatest contribution to gas exchange - due to high blood flow.
What would occur if the following occurred:
- Blockage of the alveoli opening
- Blood clot
- V/Q = 0 (zero ventilation)
- V/Q = ∞ (zero perfusion)
What is pulmonary embolism and what are its effects? PART 1
- Blood clot formation in vessels supplying lung
- Reduced lung capacity to deliver oxygen to vasculature
- V/Q = ∞ (EMBOLISED AREA - DOESN’T MAINTAIN BLOOD FLOW)
What is pulmonary embolism and what are its effects? PART 2
- Blood entering lungs is redistributed to pulmonary vascular bed
- Greater blood flow - hyperaemic
- V/Q < 1 - greater perfusion than ventilation
