Oxygen flux

O2 flux
= Amount of oxygen delivered to the peripheral tissues per minute.

• i.e. content delivered per minute
• NOT just content (which is a volume, not vol/min)

Oxygen flux

O2 flux
= O2 bound to Hb + Dissolved O2

Oxygen bound to Hb

Oxygen bound to Hb
= Cardiac output x [Hb] x SO2 x k

• CO = cardiac output (L/min)
• [Hb] (g/L)
• SO2 = saturation (as fraction)
• k is Hufner's number
  * Amount of O2 that can bind with 1g of Hb when fully saturated
  * Normal value = 1.34mLs O2/g of Hb

Dissolved O2

Dissolved O2
= CO x pO2 x 0.03

• PO2 = partial pressure (mmHg)
• 0.03mL O2 per mmHg per L of blood can be dissolved.

Total oxygen flux

Arterial O2 flux is
= 5 x 150 x 0.98 x 1.34 + 5 x 100 x 0.03
= 984.9 + 15
= appr. 1000mL O2 per min

• Assumes cardiac output of 5L/min
• Assumes [Hb] = 150g/L
• Assumes SaO2 = 98% and PO2 = 100mmHg
• pH 7.4, temp = 37

 

Similarly,

Mixed venous O2 delivery rate is
= 5 x 150 x 0.75 x 1.34 + 5 x 40 x 0.03
= 753.75 + 6
=759.75
= appro. 750mL O2 per min

• Assumes SvO2 of 75% and PvO2 of 40mmHg

 

Summary

• Total O2 flux = 1000mL O2 / min
• Arterial [O2] = 20mL O2/100mL blood
• Mixed venous [O2] = 15mL O2/100mL blood
• Normal basal consumption of O2 = 250mL/min

NB:

• PaO2 = 100mmHg
• PvO2 = 40mmHg

Or

• SaO2 = 98% (or 97.5%)
• SvO2 = 75%

Thus,

• CaO2 = 20mL O2/dL
• CvO2 = 15mL O2/dL (appro)