Resp phys review Flashcards
Alveolar Air Equation
PAO2 = FIO2(PB - PH20) - (PACO2/R)
where R = 0.8 (CO2 produced/CO2 consumed)
PB = atmospheric/barometric pressure
AaDO2
and normal values
PAO2= PaO2
<15 mmHg for people 30 years or younger
increases 3 mmHG each decate to a max of 25
Describe the V/Q relationships when comparing the apex and base of the lung
Apex:
Ventilation:
- more negative intrapleural pressure
- greater transmural pressure gradient
- larger alveoli, less ventilation
Perfusion:
- lower intravascular pressures
- less recruitment, distention
- higher resistance
- less blood flow
Base
- Ventilation:*
- opposite of all the above, so more ventilation
- Perfusion*
- opposite of all the above, so greater blood flow
Summary: more ventilation and blood flow at the base
Four major causes of hypoxemia (when PaO2 < 80)
- anatomic shunt (intracardiac or intrapulmonary)
- physiologic shunt (no V – V/Q = 0)
- Low V/Q (<1) –mucus obstruction
- hypoventilation
note: diffusion abnormalities are very uncommon cause of decreased PaO2
What is the only non-respiratory cause of hypoxemia?
low CO
Arterial PaO2, AaDO2, and PaO2 response to 100% oxygen
Anatomic Shunt
Arterial PaO2: decrease
AaDO2: increase
PaO2 response to 100% oxygen: no significant change
Arterial PaO2, AaDO2, and PaO2 response to 100% oxygen
Physiologic shunt (V/Q =0, atelectasis)
Arterial PaO2: decreased
AaDO2: increased
PaO2 response to 100%: minimal change
oxygen:Arterial PaO2, AaDO2, and PaO2 response to 100% oxygen
Low V/Q (V/Q < 1)
Arterial PaO2: decreased
AaDO2: increased
PaO2 response to 100%: increases
oxygen:Arterial PaO2, AaDO2, and PaO2 response to 100% oxygen
Hypoventilation
Arterial PaO2: decrease
AaDO2: normal
PaO2 response to 100%: increase
AArterial PaO2, AaDO2, and PaO2 response to 100% oxygen
Low FIO2
Arterial PaO2: decreased
AaDO2: normal
PaO2 response to 100%: increased
2 mechanisms of Hypercarbia (PaCo2 > 45)
- Hypoventilation (PACO2 = VCO2 / VA)
inversely related
- Increased dead space (V/Q > 1)
ventilation of an area that is not being perfused (e.g. emphysema)
Airway resistance equation
dependence on
Raw = pressure difference / flow rate
(Q = P/R)
Dependent on:
- airway radius (R = 8 nl / (pi x r4)
- lung volume: increase volume –> decrease Raw
Raw increases at lung volumes below FRC
Compliance equation
C = dV / dP
measure of lung distensibility