Editing VO2 max (section)

===Calculation: the Fick equation===
{{Main|Fick principle}}
V̇O<sub>2</sub> may also be calculated by the [[Fick principle|Fick equation]]:
<math chem>\ce{\dot VO2} = Q \times\ (C_a\ce{O2} - C_v\ce{O2})</math>, when these values are obtained during exertion at a maximal effort. Here ''Q'' is the [[cardiac output]] of the heart, ''C<sub>a</sub>''O<sub>2</sub> is the arterial oxygen content, and ''C<sub>v</sub>''O<sub>2</sub> is the venous oxygen content. (''C<sub>a</sub>''O<sub>2</sub> – ''C<sub>v</sub>''O<sub>2</sub>) is also known as the [[arteriovenous oxygen difference]].

The Fick equation may be used to measure V̇O<sub>2</sub> in critically ill patients, but its usefulness is low even in non-exerted cases.<ref>{{cite journal |last1=Thrush |first1=DN |title=Spirometric versus Fick-derived oxygen consumption: which method is better? |journal=Critical Care Medicine |date=January 1996 |volume=24 |issue=1 |pages=91–5 |doi=10.1097/00003246-199601000-00016 |pmid=8565545}}</ref> Using a breath-based VO<sub>2</sub> to estimate cardiac output, on the other hand, seems to be reliable enough.<ref>{{cite journal |last1=Fanari |first1=Z |last2=Grove |first2=M |last3=Rajamanickam |first3=A |last4=Hammami |first4=S |last5=Walls |first5=C |last6=Kolm |first6=P |last7=Saltzberg |first7=M |last8=Weintraub |first8=WS |last9=Doorey |first9=AJ |title=Cardiac output determination using a widely available direct continuous oxygen consumption measuring device: a practical way to get back to the gold standard. |journal=Cardiovascular Revascularization Medicine: Including Molecular Interventions |date=June 2016 |volume=17 |issue=4 |pages=256–61 |doi=10.1016/j.carrev.2016.02.013 |pmid=26976237 |pmc=4912455}}</ref>