Concepts in V and Q Flashcards
Conducting zone
Nose, nasopharynx, larynx, trachea, bronchi, terminal bronchioles. Warm, humidify, filter air.
Respiratory Zone
Respiratory bronchioles, alveolar ducts, alveolar sacs. Gas exchange and surfactant production.
Anatomic dead space
The volume of the conducting zone. Usually 150 ml.
Physiologic dead space
The total volume of the lungs that does not participate in gas exchange.
How is dead space measured? Equation?
Compare expired PCO2 and PA/aCO2. PECO2 should be lower by a dilution factor because it mixes with dead space air that only has O2.
Equation: Vd=Vt x [(PaCO2-PECO2)/PaCO2]
What does a Vd/Vt of 1 mean? Of zero?
1= entire lung is dead space. 0= there is no dead space.
Minute ventilation equation
V= Vt X RR, about 6 L/min
Alveolar Ventilation Equation
Va = (Vt-Vd) X RR
Partial pressure of alveolar CO2 equation
PACO2 = (VCO2 x K)/Va
Alveolar Gas Equation
Describes the relationship between PACO2 and PAO2.
PAO2 = PIO2 - (PCO2/R)
R usually = 0.8
What happens to PACO2 and PAO2 is alveolar ventilation is halved?
PACO2 doubles, but PO2 is more than halved.
Which is more constant throughout the body and in alveoli? PO2 or PCO2?
PCO2 is much more constant.
Regional Differences in Ventilation
Higher Q at the bottom because weight of lungs squeezes air out. Lower Q at the top.
V/Q ratio of a shunt?
V/Q=0, there’s perfusion without ventilation. Bypasses the alveoli.
V/Q ratio of dead space?
V/Q is infinity. There’s ventilation without perfusion.
