Flashcards in Ventilation Perfusion Matching Deck (17)
is ventilation greater at the base or the apex? what accounts for this?
it's greater at the base than the apex b/c:
1. pleural pressure is less negative at the base of the lung b/c of gravity, thus the base has lower transmural pressure
2. compliance is higher in the base than the apex
what is the effect of gravity on blood flow and ventilation?
effect on gravity on Q (6 fold) is much bigger than on V (50%)
-basis for V:Q ratio
effect of gravity on V/Q ratio
V/Q ratio greater at the top of the lung, b/c even though V and Q are lower, V is greater than Q, thus making the ratio larger
what is regional ventilation or perfusion?
the quantity of ventilation or perfusion which reaches a given region (Qr or Vr)
-both affect gas composition in alveolus, PCO2, and PO2
shunt VS alveolar dead space
shunt = perfusion w/o ventilation (low PO2, PCO2, and V/Q)
ADS = ventilation w/o perfusion (high PO2, PCO2, and V/Q)
does low V/Q (w/ low PAO2) cause vasoconstriction or vasodilation?
vasoconstriction, thus increases resistance to Q, diverting blood to better ventilated regions
-diminishes Qr, increasing V/Q, increasing PO2, decreasing PCO2
-very powerful mechanism to improve gas exchange
do low PACO2 in alveoli with high V/Q cause bronchoconstriction or bronchodilation?
bronchoconstriction, thus increasing resistance of air flow, and diverting flow to better perfused regions to decrease Vr and return PO2 to normal values
-not very strong mechanism
what does inhaling NO do?
causes vasodilation in better ventilated areas
-increases blood flow to these areas, and improves V/Q matching
what does inhaling histamine do?
causes bronchoconstriction, pulmonary vasoconstriction, and systemic vasodilation
does N2 wash out faster or slower in constricted vessels?
they wash out slowly in constricted vessels, and faster if dilated
what is MIGET?
multiple inert gas elimination technique where lung is modeled as 50 compartments
-elimination and retention of 6 different gases, and derive V/Q from the 50 compartments
how is PAO2, PaO2, CaO2, PVO2, CVO2, and FIO2 in low alveolar PO2? can O2 therapy help?
PaO2: low (normal A-a gradient)
O2 therapy helps
how is PAO2, PaO2, CaO2, PVO2, CVO2, and FIO2 in diffusion impairment? can O2 therapy help?
PaO2: (A-a gradient is increased)
O2 therapy helps
how is PAO2, PaO2, CaO2, PVO2, CVO2, and FIO2 in right to left shunt? can O2 therapy help?
PAO2: normal; PcO2 = PAO2
PaO2: low (A-a gradient is increased at level of shunt admixture)
O2 therapy can't help
how is PAO2, PaO2, CaO2, PVO2, CVO2, and FIO2 in alveolar dead space V/Q mismatch? can O2 therapy help?
PAO2: normal (functionally lower if using end-tidal PO2)
O2 therapy can help
why is PaO2 slightly less than PcO2?
due to normal shunt