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Ventilation + Gas transport
Terms in this set (14)
What is the typical VD/VT ratio in healthy individuals?
Between 0.25 and 0.35
VD = dead space
VT = tidal volume
What method can be used to measure anatomical dead space?
What method can be used to measure physiological dead space?
Anatomical dead space -> Fowler's Method
Physiological dead space -> Bohr's Method
In a healthy human adult, dead space is estimated as ...... for each pound of the subjects weight?
Wasted ventilation for a healthy 150 lb adult is about 150 ml x 12 = 1800 ml/min
12 = breathing frequency
Base of the lung
-Perfusion is higher than ventilation, so the V/Q ratio is low
-PO2 is low (due to decreased ventilation) and PCO2 is high (due to increased perfusion)
-Slightly Acidic pH (low pH/high H+)
Apex of the lung
-Perfusion is lower than ventilation, so the V/Q ratio is high
-PO2 is high (due to increased ventilation) and PCO2 is low (due to decreased perfusion)
-Slightly Alkaline pH (high pH/low H+)
Where is gas exchange most efficient, at the apex or the base of the lung? why?
Gas exchange is most efficient at the apex of the lung because it has a HIGH V/Q ratio
What condition can cause a high V/Q ratio?
How can the high ratio be normalized? How can this help?
The bronchi will constrict slightly to increase resistance and decrease ventilation from going into poorly perfused areas -> this LIMITS the amount of alveolar dead space
What condition can cause a low V/Q ratio?
How can the low ratio be normalized? How can this help?
COPD and Airway obstruction -> such as when you swallow something
Via Hypoxic vasoconstriction
Constriction of vessels in areas with low oxygen tension -> this allows the blood to be sent to better ventilated areas
What is the normal value for PO2?
What is the normal value for PCO2?
PCO2 -> 40 mmHg
What are the four respiratory causes of hypoxemia?
2. Diffusion problem
3. V/Q mismatch
If a patient comes in with Hypoxemia first we have to check if the ..... is normal?
If its normal then the cause is ....?
If its not normal then it can either be due to a ..... ,...... or ...... ?
-If this is not corrected with oxygen therapy then its a .... ? If it is corrected with oxygen therapy then its either a ..... or .... problem?
-next we check to see if the DLco is normal- if its normal then its a ..... if its not normal then its a ..... ?
Shunt, V/Q mismatch or Diffusion problem
VQ/mismatch or diffusion problem
Equilibration time for O2? CO2? N? CO?
O2 = 0.25 s
CO2 = 0.25 s + 0.5 s reserve time (if mild diffusion impairment, can still equilibrate due to this reserve time, but if severe diffusion impairment, cannot equilibrate)
N = 0.10 s
CO = does NOT equilibrate
Are the following perfusion limited or diffusion limited:
Carbon dioxide (CO2)?
Carbon monoxide (CO)?
Nitric oxide -> Perfusion limited
Oxygen (normally) -> Perfusion limited
-If the barrier thickness increases, then O2 diffusion decreases which means its now diffusion limited
Carbon dioxide -> Perfusion limited
Carbon monoxide (CO) -> Diffusion limited (there is NO equilibration in diffusion limited gases)
Diffusion limited disorders?
1. Pulmonary edema
2. Pulmonary fibrosis
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