Pulmonary Circulation Flashcards
What is the resting pressure of the pulmonary artery?
14 mmHg (25/8)
How does the pulm vasculature respond to an increase in pressure?
it does NOT auto regulate = it distends when intravascular pressure increases
Blood flow (inc or dec) from the apex to the base of the lungs. Why and how is this significant?
increases because the vascular resistance is lower at the base and pressure is higher at the base
Q = P/R
This means perfusion increases as you move from the apex to the base
Where does edema form in the lungs (in PAH)?
at the base (bc the pressure is highest there)
What keeps the lungs dry?
low pulmonary arterial pressure (low hydrostatic pressure in capillaries)
oncotic pressure in capillaries > OP in interstitial space
What effect does hypoxia have on lung arteries and arterioles?
causes them to constrict
What effect does hypercapnia have on lung arteries and arterioles?
causes them to constric
What effect does acidosis have on lung arteries and arterioles?
causes them to constrict
Blood flow to poorly perfused alveoli (inc or dec)?
decreases due to hypoxic pulmonary vasoconstriction
The greater the alveolar ventilation : Q ratio, the (higher or lower) the O2 and CO2 content.
higher O2 and lower O2
Will supplemental O2 correct a VA/Q mismatch?
yes
Will supplemental O2 correct a shunt?
no
Where is alveolar ventilation the greatest? Why?
lung base
Gravity and the lung’s weight ↑ the pleural pressure at the lung base → makes pleural pressure less negative ∴ ↓ alveolar volume → smaller alveoli are more compliant ∴ capable of more efficient ventilation.
Where is Q the greatest? Why?
lung base
Because of gravity, when a patient is upright pulmonary blood flow is highest at the base and lowest at the apex.
What does the VA/Q (alveolar ventilation/blood flow) represent?
describes how efficiently gas is exchanged
V/Q is highest in the apex and lowest in the base:
↑ V/Q (e.g., at the lung apex) → ↑ PO2, ↓ alveolar PCO2
↓ V/Q (e.g., at the lung base) → ↓ PO2, ↑ alveolar PCO2
What effect does VA/Q mismatch have on PaCO2?
No effect. PaCO2 is determined by the production of CO2 (VCO2) and the VA
VA/Q mismatch will decrease PaO2
How can PaCO2 be corrected?
increasing ventilation
How does a shunt effect PaCO2?
no effect. PaCO2 is determined by the production of CO2 (VCO2) and the VA
VA/Q mismatch will decrease PaO2
If VA/Q = 0 what is going?
VA = 0 which indicates airway obstruction
If VA/Q = infinit
Q = 0 which indicates hypotension or pulmonary embolism
When will the PO2 and PCO2 of alveolar capillary blood will approach that of mixed venous blood?
when there is no gas exchange
↑ pCO2 because it can’t be exhaled and ↓ pO2 – it can’t be inhaled
