DID SOMEONE ORDER DELIVERY

The Fick equation is used to calculate or estimate a person's oxygen consumption, also known as VO2. The assumption at the basis of the Fick equation is that any oxygen extracted into the cells from the blood stream, is also consumed within the cells. In one of the earlier posts I explained the need for systems to be able to supervise, regulate, deliver, extract, and utilize.

Since the Fick equation assumes that extraction and utilization (consumption) are one and the same, then the Fick equation covers all the processes needed to calculate oxygen consumption, being delivery of oxygen and extraction/utilization. The Fick equation calculates or estimates your VO2 (oxygen consumption) by multiplying the extent of blood circulated per minute by amount of oxygen extracted into the cells (that enters the cells).

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The amount of blood circulated per minute (L/min) is called cardiac output, and is the outcome of multiplying stroke volume, the amount of blood pumped out of the heart (left ventricle) every time the heart contracts (one beet, one pulse, one heart contraction) by heart rate, the number of times the heart contracts per minute. Stroke volume is measured in units of mL, and heart rate is measured in beats per minute (bpm).

The amount of oxygen that is left in venous blood is the outcome of how much oxygen left the blood and entered the cells (extracted) subtracted from how much oxygen existed in arterial blood to begin with. Let's remind ourself that arterial blood carried blood all the way to the cells, while venous blood carries blood away from the cells, with either substances that were not extracted into the cell or substances that have been disposed of from the cells into the blood.

Accordingly to the original Fick equation:

**VO****2**** = CO X (A-V)O****2****diff**

VO2 - oxygen consumption

CO - cardiac output; the volume of blood circulated per minute (L/min)

(A - V)O2 diff - the A represents oxygen in the arteries; the V represents oxygen in the veins; O2 diff represents the difference in oxygen content compared between arterial blood and venous blood.

If you represent the Fick equation by what each physiological measurement represents instead of the actual physiological measurement, the following equation emerges:

**VO****2**** = Blood circulation X Oxygen extraction**

Please note - for every 1,000 mL (one litter) of blood circulated, 201 mL of oxygen are offered to the cells. Thus, by knowing blood circulation volume, we know the volume of oxygen delivered to the cells (offered to the cells).

To accommodate different physiological states such physiological rest, exercise, and maximal exercise, the Fick equation allows calculating your oxygen consumption at each state. Accordingly, three equations result:

1) VO2 at rest = CO at rest X (A-V)O2diff at rest

2) VO2 during exercise = CO during exercise X (A-V)O2diff during exercise

3) Maximal VO2 = Maximal CO X Maximal (A-V)O2diff

Two more possible versions to the Fick equation can be "created" by replacing physiological measurements in the original equation with other ways to calculate them. The next version cardiac output by the physiological phrase that represents how it is calculated. Thus, this version of the Fick equation is as follows: **VO****2**** = SV X HR X (A-V)O****2****diff**

VO2 - oxygen consumption

SV - stroke volume (mL); the amount of blood pumped out of the heart every beat

HR. -heart rate (bpm); the number of heart contraction per minute

(A - V)O2 diff - the amount of oxygen extracted into the cells from the blood (oxygen that left the blood and diffused into the cells)

The amount of blood left within the left ventricle of the heart at the end of a heart's contraction (beat) is called end systolic volume (ESV, mL) is calculated as the amount of blood that existed within the ventricle to begin with, termed end diastolic volume (EDV, mL) minus the volume of blood pumped out (SV, mL). The equation that represent this is that **ESV = (EDV - SV)**.

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Manipulating this equation to extract SV on the one side, leads to the following equation: **SV = (EDV - ESV)**. Now, we can go back to the previous equation for VO2 and plug in the phrase representing SV via EDV and ESV. The result is the lest version of the Fick equation being **VO****2**** = (EDV - ESV) X HR X (A-V)O****2****diff.**

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