Lung Ventilation and Perfusion Flashcards
Why is ventilation not the same throughout the entire lung?
gravity
Describe the change in composition of the alveoli from the top to the bottom of the lung
- alveoli in top is more expanded than those at the bottom due to the weight of the lung tissue before
- alveoli at the base are compressured by the weight of the tissue above
- pleural pressure is less ar the apex than at the base of the lung
- inspiration decreases pleural pressure more
Describe how respiration changes the composition of the alveoli
- alveoli in lungs are at different lung volumes
- underinflated (smaller) alveoli at base of lung are more compliant so receive more of tidal volume
- overinflated (expanded) alveoli at the top have a lower compliance and receive less of tidal volume
What arteries supply the lungs/airways?
- pulmonary arteries: carry deoxygenated mixed venous blood from right ventricle to alveoli in lungs
- bronchial arteries: branch from aorta and supply oxygenated blood to conducting airways
Why do alveoli not fill with fluid?
- pulmonary capillaries and lymphatics have a slightly negative pressure in interstitial spaces
- excess fluid will be sucked back into interstitial space from alveoli
Describe pulmonary blood flow over zone 1 and 2 of lung
- zone 1: PA> PPA> PPV
- apex of lung under specific conditions
- no blood flow during all portions of cardiac cycle
- doesn’t occur normally
- zone 2: PPA> PA> PPV
- apex to mid lung
- intermittent blood flow only during pulmonary arterial pressure peaks
- systolic: Ppc > Palv
- diastolic: Ppc < palv
Describe pulmonary blood flow over zone 3 and 4
- zone 3: PPA> PPV> PA
- mid to lower lung
- continuous blood flow during entire CO
- Ppc > Palv
- distension of pulmonary capillaries
- zone 4: PPA> PPV> PA
- extreme base of lung
- constriction of extra-alveolar vessels
- peak flow decreases
What do bronchial arteries supply?
- smooth muscle of airways
- intrapulmonary nerves
- interstitial lung tissue
How is venous blood returned to the heart?
- through true bronchial veins
- or drains into bronchopulmonary veins where it mixes with oxygenated blood from alveoli
What is ventilation perfusion matching?
- when pulmonary blood flow is proportionally matched to pulmonary ventilation
- greatest efficiency
What is V and Q?
- V: ventilation
- Q: perfusion
What is arterial hypoexmia?
abnormal PO2 less than 80mmHg
What is hypoxia?
insufficient O2 to to carry out normal metabolic functions less than 60 mmHg
What are the 4 major causes of hypoxemia?
- anatomical shunt (perfusion that bypasses the lung)
- physiological shunt (absent ventilation to areas being perfused)
- V/Q mis-matching (low ventilation to areas being perfused)
- hypoventilation (underventilation of lung units)
Anatomical shunt
- alveolar ventilation, distribution of gas and composition normal
- distribution of CO changed as some blood now bypasses gas exchange
- right to left shunt
- hypoxemia cannot be abolished with 100% O2
- cyanotic heart disease most common
