Question

By performing relevant research, provide the precise definition for each of the following items/variables. Physiology of sport and exercise.

• Hematocrit
• Arterial-venous oxygen difference
• Venous return
• Fick equation

provide the precise definition for each. i guess you could also add an example if you'd like for each as well as a add on

Answer 1

hi,

The precise definition is as follows

Hematocrit: It is a parameter to measure the volume of red blood cells compared to the total blood volume. Normal values are Men: 40 to 54%; Women: 36 to 48 %.

Hemoglobin and hematocrit both are dependant on plasma volume (a liquid part of blood that carries cells and protein in the body). e.g. if a person is dehydrated then the hemoglobin and hematocrit will appear higher than person who is hydrated whereas in person who is overhydrated the hemoglobin and hematocrit will appear lower than the actual level.

In case of athletes, especially endurance sports, have a decreased hematocrit, sometimes called “sports anemia.” which is not anemia in a clinical sense, because athletes have in fact an increased total mass of red blood cells and hemoglobin in circulation relative to sedentary individuals. the reson for this decrease is due to intravascular hemolysis (breakdown of red blood cells [RBCs]), caused by mechanical rupture when RBCs pass through capillaries in contracting muscles, and by compression of RBCs e.g., in foot soles during running or in hand palms in weightlifters.

Arterial venus oxygen difference (Arteriovenous oxygen difference): It is a measure of amount of oxygen taken up from the blood by the tissues. e.g. At rest 5 ml of the 20 ml of oxygen in every 100 ml of blood is extracted, producing an arteriovenous oxygen difference of 5 ml. however, during exercise blood flow to the tissues increases due to increase in the demand, and haemoglobin dissociates more easily leading to widening of arteriovenous oxygen difference. In short, greater the amount of oxygen extracted by the tissues, the greater the arteriovenous oxygen difference and vice a versa.

Venous return: It is the flow of blood from the periphery back to the right atrium of heartand it is equal to cardiac output. Cardiac output is very sensitive to the pressure gradient for venous return.

e.g. an increase in mean systemic pressure (pressure that exists in the circulatory system when there is no blood motion) of only a few mm Hg, such as those occurring in muscular activity (i.e exercise) or with an increase in blood volume, will result in immediate increases in cardiac output. On the other hand, small increases in right atrial pressure (blood pressure in right atrium of the heart) of a few mm Hg, such as those occurring in acute heart failure following myocardial infarction (heart atack), will result in significant reductions in cardiac output. .

Fick equation: It is a method of measuring cardiac output (CO). It is based on the principle that uptake or release of a substance (in this case oxygen) by any organ is the product of the arteriovenous (A-V) concentration difference of the substance and the blood flow to that organ. The substance in this case is oxygen in blood. As the blood moves slowly, more oxygen is taken out of circulation and the saturations drop, and vice versa

The Fick describe following relationship

Q = M / (V - A)

Where Q: volume of blood flowing through an organ in a minute

M: The number of moles of a substance added to the blood by an organ in one minute

V and A: The venous and arterial concentrations of that substance.

Cardiac output (CO) using the Fick principle (O2 consumption) is calculated as follows:

CO = [O2 consumption (ml/min)]/A-Mixed Venous O2 difference (ml O2/ 100ml blood) x 10

e.g.

Important: O2 saturation percentages are converted to amount (or content) of O2 using the following formula: content (1.36 x hemoglobin x O2 saturation x 10).

Adapted from

https://www.ncbi.nlm.nih.gov/books/NBK259/

Front Physiol. 2013; 4: 332.

https://www.sciencedirect.com/science/article/pii/B978044310269100001X

https://www.ncbi.nlm.nih.gov/books/NBK54476/

https://www.cathlabdigest.com/articles/Measurement-Cardiac-Output-Cath-Lab-How-Accurate-It

Principle of Fick – Utilities and Limitations by Venkateshwaran S, Kerala heart journal