Intro Flashcards
What is alveolar ventilation?
Volume of gas per minute that reaches the alveoli
What is diffusion (with respect to breathing)?
Movement of CO2 and O2 across the blood-air barrier
What is perfusion?
The movement of gas into blood flow/capillary
List and describe the 2 types of dead space and approximate volume of each in a normal healthy individual.
Together they are called…
Anatomic dead space
- Includes non-perfusing areas (ex. conducting airways) ~150mL
Alveolar dead space
- Includes alveoli not participating in gas exchange ~25mL
Together they are called Physiological Dead Space.
What is the normal PO2? (in venous blood)
PO2 = 40mmHg
What is the normal PCO2? (in venous blood)
PCO2 = 46mmHg
What is the normal PAO2? (in Alveoli)
PAO2 = 100mmHg
What is the normal PACO2 (in Alveoli)
PACO2 ~ 40mmHg
What is the normal PaO2? (in arterial blood)
PaO2 ~ 95mmHg
What is the normal PaCO2 (in arterial blood)
PaCO2 ~ 40mmHg
What is the Alveolar Ventilation Equation?
PaCO2 = (Vol CO2) / (Alveolar Ventilation)
What is the Alveolar Air Equation? (ie. equation used to determine PAO2)
PAO2 = FIO2*(Patm-PH2O) - PaCO2/R
The ambient air is ____ % O2 and ____% N2.
Air is ~21% O2 and ~79% N2.
What is the normal tidal volume of a healthy individual at rest?
What volume normally reaches the alveoli?
What volume remains in conducting airways?
Tidal Vol = 500mL
Vol reaching alveoli ~ 350mL
Vol remaining in conducting pathways ~ 150mL
- (This 150mL is the dead space volume and remains relatively constant in a normal individual)
What does PaO2 measure?
The partial pressure of free O2 in arterial blood. (Does NOT measure O2 bound to Hb).
True/False… Having a PaO2 > 100mmHg will increase ability of O2 to bind to Hb.
False.
What percent of O2 in the blood is…
- dissolved in plasma?
- bound to Hb?
For O2:
..in plasma ~ 2%
..bound to Hb ~ 98%
What percent of CO2 in the blood is…
- dissolved in plasma?
- bound to Hb?
- dissolved as bicarbonate?
For CO2:
..in plasma ~ 5-10%
..bound to Hb ~ 30%
..dissolved as bicarb ~ 60%
What is O2 content?
Write the equation to determine O2 content.
O2 content is the total amount of O2 in the blood.
CaO2 = (O2 bound to Hb) + (O2 dissolved in plasma)
CaO2 = (1.34 * Hb * SaO2) + (0.003 * PaO2)
Breaking it down (and adding units) we get:
HbO2 = 1.34 (mLO2/gHb) * Hb (g/100mL) * SaO2 (%) PlasmaO2 = 0.003 * PaO2
What is O2 capacity?
The max amount of O2 that can be bound to Hb.
What is O2 saturation (SaO2)?
The % of O2 binding sites (on Hb) that are bound to O2.
What is the Bohr effect?
H+ binds to Hb and reduces its affinity for O2.
Therefore at lower pH (higher [H+]) near the tissues the O2 is released.
Hb-O2 binding affinity is inversely proportional to both [CO2] and [H+].
**Think of the Hb dissociation Curve**
What is the difference between Hypoxia and Hypoxemia?
Hypoxia = decreased O2 in the tissues
Hypoxemia = decreased O2 in the blood
What are the 5 main causes of Hypoxemia? Which is the most common?
5 is the most common.
- Decreased O2 content in air/ Low Inspired O2 “bad air”
- Hypoventilation “no air”
- Diffusion Abnormality “slow mixing”
- Shunting “no mixing”
- V/Q (Ventilation/Perfusion) Mismatch “bad mixing”
What is an example of pathology that causes diffusion abnormality?
Fibrosis of lung tissue
What are common causes of V/Q Mismatch?
- PE
- COPD
- Asthma
- Fibrosis
- Pulm HTN
Which causes of Hypoxemia have elevated…
- PaCO2?
- A-a DO2 gradients?
Can they be treated with Supplemental O2?
_Cause /// PaCO2 /// A-a DO2 grad /// Treat _
**Low inspired O2 **N N Tx with O2
**Hypoventilation ** Inc N Tx with O2
**Diffusion Problem **N E Tx with O2
**Shunting **N Inc O2 ineffective
**V/Q mismatch ** N Inc Tx with O2
*N = normal
*E = elevated with exercise, but normal at rest
