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CVPR: Pulmonary > Diffusion & Perfusion > Flashcards

Flashcards in Diffusion & Perfusion Deck (16)
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1

Solubility coeffecient definition + aO2 & aCO2

  • tendency of a molecule to dissolve in a liquid
  • aO2 = 0.0013 mM/Torr ==> oxygen is not very soluble in blood
  • aCO2 = 0.03 mM/Torr ==> CO2 ~ 20x more soluble than O2

2

Equation for arterial content of O2 (total blood concentration)

CaO2 = hemoglobin-bound O2 + freely-dissolved O2

3

ODC (oxy-hemoglobin dissociation curve) characteristics

  • relates oxygen saturation of hemoglobin (SO2) to the PO2 in blood

4

Factors that contribute to easy gas diffusion at alveoli

  • Large surface area of alveolar membrane
  • Thin alveolar membrane
  • large O2 pressure gradient between alveoli and cappilaries
    • low O2 solubility in blood +
    • O2 quickly binds to hemoglobin ==>
    • PcapO2 remains low & gradient high

5

Diseases that impact O2 diffusion

  • interstitial disease ==> thickening of alveolar wall ==> slower rate of diffusion
  • emphysema ==> breakdown of lung tissue ==> decreased surface area ==> slower diffusion
  • abnormalities in hemobglobin (e.g. anemia) ==> smaller pressure gradient ==> decreased diffusion

6

Perfusion definition/general characteristics

  • Perfusion = Q
  • amount of blood flow of pulmonary circulation available for gas exchange per min
  • Q = CO = 5L/min @ rest

7

Main factors that regulate perfusion (4)

  1. O2 tension
  2. Chemical agents
  3. Capillary recruitment
  4. Gravity

8

O2 tension regulation of perfusion

  • "O2 tension" = PAO2 
  • Low PAO2 ==> hypoxic pumonary vasoconstriction ==> decreased local blood flow and shift to other regions 

9

Chemical agents regulation of perfusion

  • Products of arachidonic acid metabolism:
    • thromboxane A2 ==> vasoconstriction
    • Prostacyclin ==> vasodilation

10

Capillary recruitment regulation of perfusion

  • moderate exercise ==> increase CO ==>
  • increased blood flow accommodated via recruitment of new capillaries

11

Gravity regulation/impact on perfusion

  • pulmonary BP @ apex << BP @ base
  • @ base ==> more capillaries open + higher blood flow

12

Major types of perfusion problems (3)

  • alveolar dead-space
  • shunts
  • ventilation/perfusion (V/Q) mismatch

13

Alveolar-dead space characteristics

  • alveoli that are well-ventilated but lack perfusion
  • no blood flow ==> no gas exchange ==> wasted ventilation 

14

Shunt characteristics

  • blood perfused regions w/out ventilation
  • small amount of shunt is normal
  • doesn't generally lead to increased arterial PCO2 (compensated by increased ventilation via central chemoreceptors)

15

V/Q mismatch characteristics

  • V/Q = ratio of ventilation versus perfusion
  • varying V/Q ratios throughout the lung ==> decreased arterial oxygenation (even when total V & Q are normal)
  • since hemoglobin is generally near saturation ==> high V/Q regions will not be able to compensate for low V/Q regions

16

Causes of V/Q mismatch

  • Gravity
  • COPD