Flashcards in Gas Exchange (Sinclair) Deck (30)
What are the 2 causes of hypoxemia present with a normal A-a difference?
1. Decreased PIO2 (altitude change)
What are the 3 causes of hypoxemia present with a widened A-a difference?
1. Diffusion limitation
2. R-to-L shunt
3. Ventilation/Perfusion (V/Q) mismatch
What does a normal A-s DO2 determine?
What does an increased A-s DO2 determine?
Lungs Functionally Divided into 2 ZONES:
conducting and respiratory
Respiratory unit served by single terminal bronchiole
Several adjacent acini with incomplete septa
What is the calculation of partial pressure for inspired gas?
= (PB - PH2O) x FIGas
VE (total ventilation) =
tidal vol x resp rate
What air does not participate in gas exchange?
Air which remains in the Conducting airways at end inspiration (anatomic dead space)
If a 500mL breath is taken, the amount of fresh gas delivered to alveoli will be:
500 - anat dead space
Alveolar Ventilation =
Minute Ventilation - Dead space
Alv Gas Equation =
PACO2 = VCO2/VA (PB-47)
Alv Gas Equation =
PIO2-PAO2 = VO2/VA (PB-47)
Alv gas equation =
PAO2 = PIO2-(PaCO2/R)
A-a difference (A-aDO2) is calculated by
subtracting PaO2 from PAO2
Widened A-a difference signifies
presence of lung disease
Normal A-a gradient signifies
no lung disease
_____ oxygen tension is readily measured by ABG
How does age affect arterial oxygen?
1. decreased oxygen transfer to blood due to declingin lung function
2. Arterial oxygen tension decreases with age
Formula for normal A-a gradient
(age + 4)/4
A-a difference (increases/decreases) with age because:
alveolar oxygen tension remains the same which arterial oxygen tension declines
Decreased oxygen tension in the circulating blood compared to normal
PaCO2 is a good measure of:
In terms of diffusion, hypoxemia only occurs if:
diffusion capacity severely decreased
transit time decreased
Hypoxemia caused by _____ does NOT correct with increased FIO2
R to L shunt
Ventilation and Perfusion are higher at the (apices/bases)
1. V/Q > 1 are called
2. V/Q < 1 are called
1. dead space-like units
2. shunt-like units
T/F: Most lung diseases cause VQ mismatch