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Cardiac output

Cardiac output is the measurement of blood flow from the heart through the ventricles, and is usually measured in liters per minute. Any factor that causes cardiac output to increase, by elevating heart rate or stroke volume or both, will elevate blood pressure and promote blood flow. These factors include sympathetic stimulation, the catecholamines epinephrine and norepinephrine, thyroid hormones, and increased calcium ion levels. Conversely, any factor that decreases cardiac output, by decreasing heart rate or stroke volume or both, will decrease arterial pressure and blood flow. These factors include parasympathetic stimulation, elevated or decreased potassium ion levels, decreased calcium levels, anoxia, and acidosis.


Compliance is the ability of any compartment to expand to accommodate increased content. A metal pipe, for example, is not compliant, whereas a balloon is. The greater the compliance of an artery, the more effectively it is able to expand to accommodate surges in blood flow without increased resistance or blood pressure. Veins are more compliant than arteries and can expand to hold more blood. When vascular disease causes stiffening of arteries, compliance is reduced and resistance to blood flow is increased. The result is more turbulence, higher pressure within the vessel, and reduced blood flow. This increases the work of the heart.

A mathematical approach to factors affecting blood flow

Jean Louis Marie Poiseuille was a French physician and physiologist who devised a mathematical equation describing blood flow and its relationship to known parameters. The same equation also applies to engineering studies of the flow of fluids. Although understanding the math behind the relationships among the factors affecting blood flow is not necessary to understand blood flow, it can help solidify an understanding of their relationships. Please note that even if the equation looks intimidating, breaking it down into its components and following the relationships will make these relationships clearer, even if you are weak in math. Focus on the three critical variables: radius (r), vessel length (λ), and viscosity (η).

Poiseuille’s equation:

Blood flow =  π ΔP r 4 8ηλ MathType@MTEF@5@5@+=feaagyart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLnhiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=xfr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaaeOqaiaabYgacaqGVbGaae4BaiaabsgacaqGGaGaaeOzaiaabYgacaqGVbGaae4DaiaabccacaqG9aGaaeiiamaalaaabaGaaeiWdiaabccacaqGuoGaaeiuaiaabccacaqGYbWaaWbaaSqabeaacaqG0aaaaaGcbaGaaeioaiaabE7acaqG7oaaaaaa@4A84@
  • π is the Greek letter pi, used to represent the mathematical constant that is the ratio of a circle’s circumference to its diameter. It may commonly be represented as 3.14, although the actual number extends to infinity.
  • ΔP represents the difference in pressure.
  • r 4 is the radius (one-half of the diameter) of the vessel to the fourth power.
  • η is the Greek letter eta and represents the viscosity of the blood.
  • λ is the Greek letter lambda and represents the length of a blood vessel.

One of several things this equation allows us to do is calculate the resistance in the vascular system. Normally this value is extremely difficult to measure, but it can be calculated from this known relationship:

Blood flow =  ΔP Resistance MathType@MTEF@5@5@+=feaagyart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLnhiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=xfr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaaeOqaiaabYgacaqGVbGaae4BaiaabsgacaqGGaGaaeOzaiaabYgacaqGVbGaae4DaiaabccacaqG9aGaaeiiamaalaaabaGaaeiLdiaabcfaaeaacaqGsbGaaeyzaiaabohacaqGPbGaae4CaiaabshacaqGHbGaaeOBaiaabogacaqGLbaaaaaa@4C0B@

If we rearrange this slightly,

Resistance =  ΔP Blood flow MathType@MTEF@5@5@+=feaagyart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLnhiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=xfr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaaeOuaiaabwgacaqGZbGaaeyAaiaabohacaqG0bGaaeyyaiaab6gacaqGJbGaaeyzaiaabccacaqG9aGaaeiiamaalaaabaGaaeiLdiaabcfaaeaacaqGcbGaaeiBaiaab+gacaqGVbGaaeizaiaabccacaqGMbGaaeiBaiaab+gacaqG3baaaaaa@4C0B@

Questions & Answers

Which of the following is generally called a Sprain?
Raneem Reply
sprain is also called torn ligament.. it is the streching Or tearing of ligament.. with in a joint
a long boin between your nick and pelvic
sprain is also known as" moch"
sprain is also known as 'moch' it's a type of injury affect on ligaments..(sprain)
sprain and strain both called as 'moch'
body, muscle and regional of structures in the body
Harmony Reply
when the heart beats, blood pumps through the body and making the body function
what is vagina
Hausa Reply
what is ventricular circulation
Maryam Reply
In a four-chambered heart, such as that in humans, there are two ventricles that operate in a double circulatory system: the right ventricle pumps blood into the pulmonary circulation to the lungs, and the left ventricle pumps blood into the systemic circulation through the aorta.
A 23-year-old basketball player mentally rehearses free throw shots while lying in bed. Which option best describesthe area of the brain that is involved in generating a motor image of this action in the absence of actual movement?
a 67-year-old man has a stroke. one week later, he experiences sudden and uncontrolled flailing, ballistic movements of his limbs. which part of the man’s brain is most likely to have been damaged by the stroke?
primary motor cortex.. (principal area of cerebrum)
what factors that affect the rate diffusion
Gift Reply
the mass of the solute the temperature of theenvironment the solvent density and the distance traveled
sorry what are the common meaning of haemostatis
Juma Reply
homeostasis is the steady internal physical and chemical conditions maintaining by living systems
what are the negatives feedback regulation of ADH
Nansi Reply
what is the the differences between DNA and RNA?
The major differences between the DNA and RNA are contain of double stranded and single stranded which the DNA contain duoble stranded and RNA contain single stranded.
what are the negatives feedback regulation of ADH before this we confused just verify long term of ADH firstly
How many genes consist of DNA?
omaryare muhyadiin when you talk about genes, is the material formed in a DNA genes have form like plasma have many genes round there
aldosterone, renin
DNA contains the sugar deoxyribone while RNA contains the sugar ribose the only difference between ribose and deoxyribone is that ribose has one more- OH group than deoxyribone which has -H attached to the second carbon in the ring DNA is a double stranded molecules RNA is a single strnded molecul
in human genes very in size from a few hundred DNA based to more than 2million bases
to know the different structures of the body To know how the body works To know more about our body parts
Deitdre Reply
hi Deitdre you tock about knowledge or you ask the question
do you need any explanation when reading this book?
janet Reply
Its Good
if have many ability just do it!!
we all waiting for it
compare and contrast the operation of homeostasis
Dinelle Reply
what is the difference between an ionic, polar covalent and nonpolar covalent bond?
In summary, the bond has different in electronegativity.
sorry help me to get the definition of hemostasis or the meaning
the definition of distal
Dinelle Reply
farthest away from the attachment point.
Distal, is the farthest possition from the origin or midle point
exercise physiologist how ?
Noor Reply
hi noorr. when you talk about physiologist its a person who study physiology but exercise physiologist is what an exercise doing by physiologist in physiologican
can I get the questions of human physiology that is present in HSC 2nd semester
Rafiullah Reply
in my lerning the question com like for example ni eassy qustion must understand the the part of the body and how it work or mechanisms of each part learned
how can I memorize
mukhtaar Reply
which part of the body produces blood
give me answer
Red blood cells are formed in the red bone marrow ofbones. Stem cells in the red bone marrow called hemocytoblasts give rise to all of the formed element
what is hemocytoblasts
hemocytoblasts are stem cells in red bone marrow which give rise the all of formed elements
Discuss clonal theory in physiology and its application in measles infection in a 6yr child? Can anyone help me
Isaac Reply

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