Resp phys review

Question 1

Alveolar Air Equation

Answer 1

P_AO₂ = F_IO₂(P_B - P_H20) - (P_ACO₂/R)

where R = 0.8 (CO2 produced/CO2 consumed)

P_B = atmospheric/barometric pressure

Question 2

AaDO₂

and normal values

Answer 2

P_AO2= P_aO2

<15 mmHg for people 30 years or younger

increases 3 mmHG each decate to a max of 25

Question 3

Describe the V/Q relationships when comparing the apex and base of the lung

Answer 3

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

Question 4

Four major causes of hypoxemia (when P_aO₂ < 80)

Answer 4

1. anatomic shunt (intracardiac or intrapulmonary)
2. physiologic shunt (no V – V/Q = 0)
3. Low V/Q (<1) –mucus obstruction
4. hypoventilation

note: diffusion abnormalities are very uncommon cause of decreased PaO2

Question 5

What is the only non-respiratory cause of hypoxemia?

Answer 5

low CO

Question 6

Arterial PaO_2, AaDO₂, and PaO₂ response to 100% oxygen

Anatomic Shunt

Answer 6

Arterial PaO2: decrease

AaDO2: increase

PaO2 response to 100% oxygen: no significant change

Question 7

Arterial PaO2, AaDO2, and PaO2 response to 100% oxygen

Physiologic shunt (V/Q =0, atelectasis)

Answer 7

Arterial PaO2: decreased

AaDO2: increased

PaO2 response to 100%: minimal change

Question 8

oxygen:Arterial PaO2, AaDO2, and PaO2 response to 100% oxygen

Low V/Q (V/Q < 1)

Answer 8

Arterial PaO2: decreased

AaDO2: increased

PaO2 response to 100%: increases

Question 9

oxygen:Arterial PaO2, AaDO2, and PaO2 response to 100% oxygen

Hypoventilation

Answer 9

Arterial PaO2: decrease

AaDO2: normal

PaO2 response to 100%: increase

Question 10

AArterial PaO2, AaDO2, and PaO2 response to 100% oxygen

Low F_IO₂

Answer 10

Arterial PaO2: decreased

AaDO2: normal

PaO2 response to 100%: increased

Question 11

2 mechanisms of Hypercarbia (PaCo2 > 45)

Answer 11

1. Hypoventilation (P_ACO2 = VCO2 / V_A)

inversely related

2. Increased dead space (V/Q > 1)

ventilation of an area that is not being perfused (e.g. emphysema)

Question 12

Airway resistance equation

dependence on

Answer 12

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

Question 13

Compliance equation

Answer 13

C = dV / dP

measure of lung distensibility