Hepatic circulation

[Ref: KB2: p72;BL8:p262;WG21:p627]

Some liver-specific figures:

• 30% of cardiac output
• 20% of body oxygen consumption

Hepatic blood flow

Total hepatic blood flow

= 30% of cardiac output

= 1500 mL/min

[KB2:p72]

• Hepatic artery = 300-500mL/min
  * 20-33%
• Portal vein = 1000-1200mL/min
  * 66-80%

[BL8:p262]

• Hepatic artery = 25% of blood supply
  * BP = 90mmHg
• Portal vein = 75% of blood supply
  * BP = 10mmHg

Autoregulation

• Portal vein supply is NOT autoregulated, but dependent on bowel activity.
• Hepatic artery flow adjusts (reciprocally) to changes in portal vein flow
• Adenosine produced from metabolism may play a role
  --> Decreased portal vein blood flow
  --> Buildup of adenosine
  --> Hepatic artery vasodilation
  [WG21:p627]

Normal values for blood pressures

• Mean arterial BP = 90mmHg
  = Hepatic artery
• Portal venous BP = 10mmHg
• Hepatic venous BP = 5mmHg

Hepatic oxygen consumption

Hepatic oxygen consumption

= 20% of body oxygen consumption

= 50mLs O2/min

Sources of oxygen supplied

[KB2: p72]

• Hepatic artery = 40-50%
• Portal vein = 50-60%

[BL8:p262]

• Hepatic artery = 75%
• Portal vein = 25%
• i.e. Reversed from blood supply

Measurement

• Indocyanine green is used as dye for hepatic blood flow measurement
• Level is measured using infrared at 805nm wavelength
  * 805nm is also the isobestic point, so measurement is not affected by oxygenation
  * Presence of indocyanine green does underestimates the SpO2 reading
• Blood is needed from
  * Peripheral vein (=peripheral artery = hepatic artery level)
  * AND hepatic vein

Other notes

• Contains 15% of total blood volume
  --> Half (7.5%) can be released by sympathetic vasoconstriction