Measurement of blood flow

Coronary blood flow

Kety-Schmidt method

??????Any other methods

Cerebral blood flow

Kety-Schmidt method

Amount of N2O taken up by brain per unit time = CBF x a-V difference of N2O across brain

Also used to measure coronary blood flow

[TF8: p186]

Renal blood flow

Use of PAH to measure effective renal plasma flow (RPF)

Clearance of PAH
= Urine PAH content (per unit time) / Plasma [PAH]
= Effective RPF

Effective renal blood flow
= Effective RPF / (1-Hct)

NB:

• Venous blood [PAH] is used because it would be the same as the concentration in any other arteries, including the renal artery

Hepatic blood flow

Use of hepatic extraction of bromsulphalein or indocyanine green

Dye is removed only in liver, and it has no enterohepatic circulation

Method

Constant infusion till steady state

Blood taken from peripheral veins (which would have the same level as hepatic artery) and from hepatic vein using a catheter

Measurement is using spectrophotometry using peak absorption at 805nm, which is also the isobestic point for haemoglobin
--> Oxygen saturation will not influence result