Arteriovenous oxygen difference
Encyclopedia
The arteriovenous oxygen difference, or a-vO2 diff, is the difference in the oxygen
content of the blood
between the arterial blood
and the venous blood
. It is an indication of how much oxygen is removed from the blood in capillaries
as the blood circulates
in the body. The a-vO2 diff and cardiac output
are the main factors that allow variation in the body's total oxygen consumption, and are important in measuring VO2
. The a-vO2 diff is usually measured in millilitres of oxygen per 100 millilitres of blood (mL/100 mL).
, brachial
, or radial artery
and the oxygen concentration in the deoxygenated blood from the mixed supply found in the pulmonary artery
(as an indicator of the typical mixed venous supply).
Put in simple terms:
The usual unit for a-vO2 diff is millilitres of oxygen per 100 millilitres of blood (mL/100 mL), however, particularly in medical uses, other units may be used, such as micromoles
per millilitre (μmol/mL).
In practice, a-vO2 diff may be determined using the Fick Principle
rather than by taking direct blood samples. In order to do so oxygen consumption (VO2) may be measured using a spirometer
to detect gaseous concentrations in exhaled air compared to inhaled air, while cardiac output
can be determined using a Doppler ultrasound.
Arterial blood will generally contain an oxygen concentration of around 20 mL/100 mL. Venous blood with an oxygen concentration of 15 mL/100 mL would therefore lead to typical values of the a-vO2 diff at rest of around 5 mL/100 mL. During intense exercise, however, the a-vO2 diff can increase to as much as 16 mL/100 mL due to the working muscles
extracting far more oxygen from the blood than they do at rest.
Alternatively, in order to find the efficiency of the lungs in replenishing blood oxygen levels, the a-vO2 diff may instead be taken by comparing blood from the pulmonary artery and the pulmonary vein
; in this case a negative value for a-vO2 diff would be obtained as the oxygen content of the blood would have increased.
leads to an increase in the arteriovenous oxygen difference in all individuals. As exercise intensities increase, the muscles increase the amount of oxygen they extract from the blood and this therefore results in further increases in a-vO2 diff.
The maximum a-vO2 diff is also usually greater in trained athletes than in untrained individuals. This is a result of aerobic exercise
leading to hypertrophy
of the slow twitch muscle fibres mainly due to increased capillarisation. The increase in capillary beds in the muscle means that blood supply to that muscle can be greater and diffusion
of oxygen, carbon dioxide
, and other metabolite
s increases. With training the muscles also improve in their ability to extract oxygen from the blood and process the oxygen, possibly due to adaptations of the mitochondria
and an increase in the muscle's myoglobin
content.
Research has shown that following the commencement of exercise there is a delay in the increase of the a-vO2 diff, and that a-vO2 diff only has a marginal impact in the total change in VO2 in the early stages of exercise. The bulk of the early increase in oxygen consumption after a sudden change in exercise levels results from increased cardiac output. However it has also been found that the increase in the maximal a-vO2 diff resulting from adaptations to a physical training program can account for most of the difference in VO2 max
in subjects participating in sub-maximal exercise.
and medical research. For example the a-vO2 diff has been used to measure cerebral blood flow
in coma
tose patients, assisting with their diagnosis
and treatment
. The a-vO2 diff has also been used to determine the effects of physical training in coronary patients
.
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
content of the blood
Blood
Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....
between the arterial blood
Arterial blood
Arterial blood is the oxygenated blood in the circulatory system found in the lungs, the left chambers of the heart, and in the arteries. It is bright red in color, while venous blood is dark red in color...
and the venous blood
Venous blood
Venous blood is deoxygenated blood in the circulatory system. It runs in the systemic veins from the organs to the heart. Deoxygenated blood is then pumped by the heart to lungs via the pulmonary arteries, one of the few arteries in the body that carries deoxygenated blood .Venous blood is...
. It is an indication of how much oxygen is removed from the blood in capillaries
Capillary
Capillaries are the smallest of a body's blood vessels and are parts of the microcirculation. They are only 1 cell thick. These microvessels, measuring 5-10 μm in diameter, connect arterioles and venules, and enable the exchange of water, oxygen, carbon dioxide, and many other nutrient and waste...
as the blood circulates
Circulatory system
The circulatory system is an organ system that passes nutrients , gases, hormones, blood cells, etc...
in the body. The a-vO2 diff and cardiac output
Cardiac output
Cardiac output is the volume of blood being pumped by the heart, in particular by a left or right ventricle in the time interval of one minute. CO may be measured in many ways, for example dm3/min...
are the main factors that allow variation in the body's total oxygen consumption, and are important in measuring VO2
VO2 max
VO2 max is the maximum capacity of an individual's body to transport and use oxygen during incremental exercise, which reflects the physical fitness of the individual...
. The a-vO2 diff is usually measured in millilitres of oxygen per 100 millilitres of blood (mL/100 mL).
Measurement
The arteriovenous oxygen difference is usually taken by comparing the difference in the oxygen concentration of oxygenated blood in the femoralFemoral artery
The femoral artery is a general term comprising a few large arteries in the thigh. They begin at the inguinal ligament and end just above the knee at adductor canal or Hunter's canal traversing the extent of the femur bone....
, brachial
Brachial artery
The brachial artery is the major blood vessel of the arm.It is the continuation of the axillary artery beyond the lower margin of teres major muscle. It continues down the ventral surface of the arm until it reaches the cubital fossa at the elbow. It then divides into the radial and ulnar arteries...
, or radial artery
Radial artery
In human anatomy, the radial artery is the main blood vessel, with oxygenated blood, of the lateral aspect of the forearm.-Course:The radial artery arises from the bifurcation of the brachial artery in the cubital fossa. It runs distally on the anterior part of the forearm...
and the oxygen concentration in the deoxygenated blood from the mixed supply found in the pulmonary artery
Pulmonary artery
The pulmonary arteries carry deoxygenated blood from the heart to the lungs. They are the only arteries that carry deoxygenated blood....
(as an indicator of the typical mixed venous supply).
Put in simple terms:
- a-vO2 diff = Ca – Cv
- where:
- Ca = the oxygen concentration of arterial blood (oxygenated blood)
- Cv = the oxygen concentration of venous blood (deoxygenated blood)
- where:
The usual unit for a-vO2 diff is millilitres of oxygen per 100 millilitres of blood (mL/100 mL), however, particularly in medical uses, other units may be used, such as micromoles
Mole (unit)
The mole is a unit of measurement used in chemistry to express amounts of a chemical substance, defined as an amount of a substance that contains as many elementary entities as there are atoms in 12 grams of pure carbon-12 , the isotope of carbon with atomic weight 12. This corresponds to a value...
per millilitre (μmol/mL).
In practice, a-vO2 diff may be determined using the Fick Principle
Fick principle
Developed by Adolf Eugen Fick , the Fick principle was first devised as a technique for measuring cardiac output. However, its underlying principles may be applied in a variety of clinical situations....
rather than by taking direct blood samples. In order to do so oxygen consumption (VO2) may be measured using a spirometer
Spirometer
A spirometer is an apparatus for measuring the volume of air inspired and expired by the lungs. It is a precision differential pressure transducer for the measurements of respiration flow rates. The spirometer records the amount of air and the rate of air that is breathed in and out over a...
to detect gaseous concentrations in exhaled air compared to inhaled air, while cardiac output
Cardiac output
Cardiac output is the volume of blood being pumped by the heart, in particular by a left or right ventricle in the time interval of one minute. CO may be measured in many ways, for example dm3/min...
can be determined using a Doppler ultrasound.
Arterial blood will generally contain an oxygen concentration of around 20 mL/100 mL. Venous blood with an oxygen concentration of 15 mL/100 mL would therefore lead to typical values of the a-vO2 diff at rest of around 5 mL/100 mL. During intense exercise, however, the a-vO2 diff can increase to as much as 16 mL/100 mL due to the working muscles
Skeletal muscle
Skeletal muscle is a form of striated muscle tissue existing under control of the somatic nervous system- i.e. it is voluntarily controlled. It is one of three major muscle types, the others being cardiac and smooth muscle...
extracting far more oxygen from the blood than they do at rest.
Alternatively, in order to find the efficiency of the lungs in replenishing blood oxygen levels, the a-vO2 diff may instead be taken by comparing blood from the pulmonary artery and the pulmonary vein
Pulmonary vein
The pulmonary veins are large blood vessels that carry blood from the lungs to the left atrium of the heart. In humans there are four pulmonary veins, two from each lung...
; in this case a negative value for a-vO2 diff would be obtained as the oxygen content of the blood would have increased.
Impacts of exercise
Physical exercisePhysical exercise
Physical exercise is any bodily activity that enhances or maintains physical fitness and overall health and wellness. It is performed for various reasons including strengthening muscles and the cardiovascular system, honing athletic skills, weight loss or maintenance, as well as for the purpose of...
leads to an increase in the arteriovenous oxygen difference in all individuals. As exercise intensities increase, the muscles increase the amount of oxygen they extract from the blood and this therefore results in further increases in a-vO2 diff.
The maximum a-vO2 diff is also usually greater in trained athletes than in untrained individuals. This is a result of aerobic exercise
Aerobic exercise
Aerobic exercise is physical exercise of relatively low intensity that depends primarily on the aerobic energy-generating process. Aerobic literally means "living in air", and refers to the use of oxygen to adequately meet energy demands during exercise via aerobic metabolism...
leading to hypertrophy
Hypertrophy
Hypertrophy is the increase in the volume of an organ or tissue due to the enlargement of its component cells. It should be distinguished from hyperplasia, in which the cells remain approximately the same size but increase in number...
of the slow twitch muscle fibres mainly due to increased capillarisation. The increase in capillary beds in the muscle means that blood supply to that muscle can be greater and diffusion
Diffusion
Molecular diffusion, often called simply diffusion, is the thermal motion of all particles at temperatures above absolute zero. The rate of this movement is a function of temperature, viscosity of the fluid and the size of the particles...
of oxygen, carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
, and other metabolite
Metabolite
Metabolites are the intermediates and products of metabolism. The term metabolite is usually restricted to small molecules. A primary metabolite is directly involved in normal growth, development, and reproduction. Alcohol is an example of a primary metabolite produced in large-scale by industrial...
s increases. With training the muscles also improve in their ability to extract oxygen from the blood and process the oxygen, possibly due to adaptations of the mitochondria
Mitochondrion
In cell biology, a mitochondrion is a membrane-enclosed organelle found in most eukaryotic cells. These organelles range from 0.5 to 1.0 micrometers in diameter...
and an increase in the muscle's myoglobin
Myoglobin
Myoglobin is an iron- and oxygen-binding protein found in the muscle tissue of vertebrates in general and in almost all mammals. It is related to hemoglobin, which is the iron- and oxygen-binding protein in blood, specifically in the red blood cells. The only time myoglobin is found in the...
content.
Research has shown that following the commencement of exercise there is a delay in the increase of the a-vO2 diff, and that a-vO2 diff only has a marginal impact in the total change in VO2 in the early stages of exercise. The bulk of the early increase in oxygen consumption after a sudden change in exercise levels results from increased cardiac output. However it has also been found that the increase in the maximal a-vO2 diff resulting from adaptations to a physical training program can account for most of the difference in VO2 max
VO2 max
VO2 max is the maximum capacity of an individual's body to transport and use oxygen during incremental exercise, which reflects the physical fitness of the individual...
in subjects participating in sub-maximal exercise.
In medicine
Arteriovenous oxygen difference is also used in other areas of study such as medicineMedicine
Medicine is the science and art of healing. It encompasses a variety of health care practices evolved to maintain and restore health by the prevention and treatment of illness....
and medical research. For example the a-vO2 diff has been used to measure cerebral blood flow
Cerebral blood flow
Cerebral blood flow, or CBF, is the blood supply to the brain in a given time. In an adult, CBF is typically 750 millitres per minute or 15% of the cardiac output. This equates to 50 to 54 millilitres of blood per 100 grams of brain tissue per minute. CBF is tightly regulated to meet the brain's...
in coma
Coma
In medicine, a coma is a state of unconsciousness, lasting more than 6 hours in which a person cannot be awakened, fails to respond normally to painful stimuli, light or sound, lacks a normal sleep-wake cycle and does not initiate voluntary actions. A person in a state of coma is described as...
tose patients, assisting with their diagnosis
Diagnosis
Diagnosis is the identification of the nature and cause of anything. Diagnosis is used in many different disciplines with variations in the use of logics, analytics, and experience to determine the cause and effect relationships...
and treatment
Treatment
Treatment may refer to:* Treatment, therapy used to remedy a health problem* Treatment, a process or intervention in the design of experiments* Treatment group, a collection of items or individuals given the same treatment in an experiment* Water treatment...
. The a-vO2 diff has also been used to determine the effects of physical training in coronary patients
Coronary disease
Coronary disease refers to the failure of coronary circulation to supply adequate circulation to cardiac muscle and surrounding tissue. It is already the most common form of disease affecting the heart and an important cause of premature death in Europe, the Baltic states, Russia, North and South...
.