Resp phys review Flashcards

1
Q

Alveolar Air Equation

A

PAO2 = FIO2(PB - PH20) - (PACO2/R)

where R = 0.8 (CO2 produced/CO2 consumed)

PB = atmospheric/barometric pressure

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2
Q

AaDO2

and normal values

A

PAO2= PaO2

<15 mmHg for people 30 years or younger

increases 3 mmHG each decate to a max of 25

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3
Q

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

A

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

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4
Q

Four major causes of hypoxemia (when PaO2 < 80)

A
  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

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5
Q

What is the only non-respiratory cause of hypoxemia?

A

low CO

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6
Q

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

Anatomic Shunt

A

Arterial PaO2: decrease

AaDO2: increase

PaO2 response to 100% oxygen: no significant change

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7
Q

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

Physiologic shunt (V/Q =0, atelectasis)

A

Arterial PaO2: decreased

AaDO2: increased

PaO2 response to 100%: minimal change

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8
Q

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

Low V/Q (V/Q < 1)

A

Arterial PaO2: decreased

AaDO2: increased

PaO2 response to 100%: increases

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9
Q

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

Hypoventilation

A

Arterial PaO2: decrease

AaDO2: normal

PaO2 response to 100%: increase

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10
Q

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

Low FIO2

A

Arterial PaO2: decreased

AaDO2: normal

PaO2 response to 100%: increased

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11
Q

2 mechanisms of Hypercarbia (PaCo2 > 45)

A
  1. Hypoventilation (PACO2 = VCO2 / VA)

inversely related

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

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

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12
Q

Airway resistance equation

dependence on

A

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

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13
Q

Compliance equation

A

C = dV / dP

measure of lung distensibility

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