[profound (OP)]

I have done some googling and come up with confusing answers.The blood speed in the human body varies from a 5 cm/sec to 5 cm/per hour.

i mean what is the speed of Red Blood in the wrist pulse points.it seems to be very poorly researched by those over paid "researchers2.

[Colin2B]

I don't understand why you find this confusing. The velocity will vary with the cross sectional area of the particular vessel, and blood pressure at any particular part of the heartbeat. So you will get wide variation of the numbers.
However, it has been well researched by people who know what they are doing, but are often underpaid.

[chris]

We've chatted about this topic on a number of occasions.

The simplest way to look at it is to consider that, in a minute, the heart pumps about 5 litres of blood (70 beats per minute, each ejecting about 70 ml of blood); since your total blood volume is about 5 litres, then you are circulating the equivalent of your entire blood volume per minute, which means that an average red blood cell would take a minute to transit.

This is the approach taken in this answer: https://www.thenakedscientists.com/articles/questions/how-quickly-does-blood-cell-circulate

However, the situation is slightly more complex because the above assumes that cells all make the same journey and within the same time. But this is an oversimplification; there are some vascular beds, such as the spleen, liver and bone marrow, where red cell transit times are slower for various reasons. A red cell whooshing up your carotid arteries and through the brain, on the other hand, is likely to complete the journey much more rapidly.

This line of reasoning is considered in this thread from this forum and the suggested red cell lap time is about half a minute:

https://www.thenakedscientists.com/forum/index.php?topic=9969.0

Therefore, I would hedge my bets and say tha the average red cell takes less than a minute, and probably closer to thirty seconds, to complete a lap of the body.

[evan_au]

I have watched an ultrasound machine used in "Doppler" mode, where reflections from red blood cells (and white cells) are used to measure the velocity of the blood.
Flows toward towards and away from the sensor were colored red and blue ("red-shifted" and "blue-shifted" ultrasound).

This machine is able to measure the velocity along the beam (but is not so good at measuring the velocity across the path of the beam),

Those guys would have a good idea of typical velocities.

[evan_au]

This video gives a good idea of the velocity:
- It shows that the velocity is very different in small and large vessels
- In capillaries, the red blood cells barely squeeze through
- It shows that the speed changes over time (and sometimes even reverses - presumably when there is muscle activity)
- You can work out the velocity by comparing the diameter of a red blood cell with how far it moves in a second.

See: https://www.youtube.com/watch?v=4yBMY9Wj7z0

Link: www.youtube.com/watch?v=4yBMY9Wj7z0

[chris]

watched an ultrasound machine used in "Doppler" mode, where reflections from red blood cells (and white cells) are used to measure the velocity of the blood.

Good point. These, and other, sorts of measurements indicate that the flow rate through a large artery, like the aorta, is about 30 metres per second. We'll assume that the blood moves homogeneously at this rate, otherwise the heart would end up pumping sludge (cells) and all that would come out at the other end would be water. Measure a capillary though, or a vein, and the flow rate is much lower.

So blood, during certain stages of its journey, travels very fast and at other stages travels very slowly. One must be cautious of taking a single snapshot of one part of the system and then extrapolating that to the system as a whole.