[networkguy]

Originally Posted by fgummett

Perhaps in the large vessels but what about the capillary system.. which is where we do our home BG testing. Put it this way... a large cut to a major vessel such as the femoral artery in the upper leg and yes we can bleed out in a matter of minutes but is the same true if you cut your hand?

No, not just in the large vessels. (Not trying to argue here) but its a medical fact it takes 1- 1.5 mins for a full round of circulation. Unless capillaries are somehow left out of circulation?

[fgummett]

You live in Arizona right? Imagine you get bitten by a rattler on your forearm... are you saying that venom will have circulated all around your body in about a minute... I sure hope that is not the case.

[networkguy]

Originally Posted by fgummett

You live in Arizona right? Imagine you get bitten by a rattler on your forearm... are you saying that venom will have circulated all around your body in about a minute... I sure hope that is not the case.

So are you saying 1-1.5 min for full round of circulation is wrong? Do you have any links to support that? I can put up about 100 or so that says it does Its a medical fact man

[fgummett]

This might help to explain both your medical fact and also why there is a potential for delay in BG between forearm readings and fingertips

from: Fundamentals of physiology By Lauralee Sherwood. Fundamentals of physiology: a human ... - Google Books

The velocity of flow is the linear speed, or distance per unit of time, with which blood flows forward through a given segment of the circulatory system. Because the circulatory system is a closed system, the volume of blood flowing through any level of the system must equal the cardiac output. For example, if the heart pumps out 5 liters of blood per minute, and 5 liters/min returns to the heart, then 5 liters/min must flow through the arteries, arterioles, capillaries, and veins. Therefore, the flow rate is the same at all levels of the circulatory system.
However, the velocity with which the blood flows through the different segments of the vascular tree varies, because velocity of flow is inversely proportional to the total cross-section area of all the vessels at any given level of the circulatory system. Even though the cross-section area of each capillary is extremely small compared to that of the large aorta, the total cross-section area of all the capillaries added together is about 1300 times greater than the cross-section area of the aorta because there are so many capillaries. Accordingly, blood slows considerably as it passes through the capillaries. This slow velocity allows adequate time for exchange of nutrients and metabolic end products between blood and tissue cells, which is the sole purpose of the circulatory system. As the capillaries rejoin to form veins, the total cross-ection area is once again reduced, and the velocity of blood flow increase as blood returns to the heart.
As an analogy, consider a river (the arterial system) that widens into a lake (the capillaries), then narrows into a river again (the venous system). The flow rate is the same throughout the length of this body of water; that is, identical volumes of water are flowing past all the points along the bank of the river and lake. However, the velocity of flow is slower in the wide lake than in the narrow river because the identical volume of water, now spread out over a larger cross-section area, moves forward a much shorter distance in the wide lake than in the narrow river during a given period of time. You could readily observe the forward movement of water in the swift flowing river, but the forward motion of water in the lake would be unnoticeable.

Consider the "river-lake-river" analogy above and imagine emptying a bag of small yellow plastic ducks into the upper river (to represent cells carrying blood glucose)... they rush quickly down the first river and then drift slowly across the lake before finally exiting into the river at the far side.

The fingers have larger vessels serving them than the top of the forearm does.

[networkguy]

Originally Posted by fgummett

This might help to explain both your medical fact and also why there is a potential for delay in BG between forearm readings and fingertips

Consider the "river-lake-river" analogy above and imagine emptying a bag of small yellow plastic ducks into the upper river (to represent cells carrying blood glucose)... they rush quickly down the first river and then drift slowly across the lake before finally exiting into the river at the far side.

The fingers have larger vessels serving them than the top of the forearm does.

I understand. What doesnt make sense is...if blood makes full circulation in <90 secs, how can that exclude capillary flow? Its a closed system. In the analogy above, its not. Therefore, volume/sq centimeter is irrelevant. A full cycle is a full cycle. Unless Im missing something.

[Grunch]

Originally Posted by networkguy

I understand. What doesnt make sense is...if blood makes full circulation in <90 secs, how can that exclude capillary flow? Its a closed system. In the analogy above, its not. Therefore, volume/sq centimeter is irrelevant. A full cycle is a full cycle. Unless Im missing something.

Just because the heart pumps 5L it doesn't mean that all the blood completes a full cycle. Some of the blood completes more than one cycle while other parts of the blood move less.

[networkguy]

Originally Posted by Grunch

Just because the heart pumps 5L it doesn't mean that all the blood completes a full cycle. Some of the blood completes more than one cycle while other parts of the blood move less.

Hm. I dont know how that is possible with a closed loop system. Im still Googleing to find that out, but so far everything Ive read says 45 secs-2 mins for full cycle. If you know of a link please let me know!

(still looking)

[networkguy]

Hm couldnt edit my post above (and dont mean for this to go so OT) but my understanding is the same as this question asked in a medical forum:

Does rate of blood flow across capillaries slow? | Study Question Q&A | Student Doctor Network

Does rate of blood flow across capillaries slow?

the thinner the radius, the faster the flow, and this would be true if 1 vein turned into 1 artery. But 1 vein branches off, so velocity actually slows. If you were to add up the volume of all the capillaries, they would hold more volume than a single vein, so the velocity slows.

and

All of the blood that leaves the aorta has to end up in the arteries, and all of the blood that leaves the arteries has to end up in the arterioles and so on and so forth. If the flow were not the same from all of the arteries to all of the arterioles, then you would necessarily have to have a build up of blood pooling somewhere in the circulation.

(still looking)

[Cluck]

Originally Posted by networkguy

I cant believe so many of you still use your fingers for glucose test...I switched to forearm about 5 years ago and doing 5-10/day its a dream.

And, unless Ive been out sweating or getting grungy, I never use alcohol first.

The reading you get from a test on your forearm is delayed by about 20 minutes. This can be crucial for a Type I whose BG could be rising or falling very fast.

[Cluck]

LoL I should have read all the posts before posting the above I guess.

Whole can of worms (or rather snakes) it seems.

Whatever, as a Type I who can sometimes have very unstable BGs I will continue to use my fingertips on the advisement of numerous professional medical practitioners.

[Granny Shanny]

Originally Posted by Cluck

LoL I should have read all the posts before posting the above I guess.

Whole can of worms (or rather snakes) it seems.

Hey - it happens to the best of us! lol!

[fgummett]

Here's a few more snips from the above book (which I again typed in handraulically as there is no copy and paste )

Each capillary is so narrow (7 µm average diameter) that red blood cells (8 µm diameter) have to squeeze through single file.
...
Researchers estimate that because of extensive capillary branching, no cell is farther than 0.01 cm (4/1000 inch) from a capillary
....
Because capillaries are distributed in such incredible numbers (estimates range from 10 - 40 billion capillaries), a tremendous total surface area is available for exchange (an estimated 600 [square meters]). Despite the large number of capillaries, at any one point in time they contain only 5% of the total blood volume (250 ml out of a total of 5000 ml).
...
Blood flows more slowly in the capillaries than elsewhere in the circulatory system. The extensive capillary branching is responsible for this slow velocity of blood flow through the capillaries.

I find I have to stop thinking about the circulatory system as plastic plumbing pipes... hopefully the above detail shows that we are dealing with a whole different scale Think again of the lake representing ALL the capillaries -- and as above we only have 250 ml of blood in there -- I can see how 5 litres/min flows into the system but the lake is almost like a buffer zone that absorbs some of that volume for a while but that there can still be 5litres/min leaving the lake. Perhaps the total volume of blood is closer to 5,250 ml but the overall flow is 5,000ml/minute Maybe a better analogy would be "river-marsh/wetlands-river".

---

As to the quotes from a medical forum, I really hope they are not indicative of the state of our future Doctors: Arteries carry blood from the heart, Veins carry blood back to the heart. Veins do not branch into Arteries.

[fgummett]

Here's another analogy: think of a large bath sponge held under a tap... at first no water comes through the sponge -- so we may deduce that it has retarded the water flow -- once the sponge is saturated, water will leave the bottom of the sponge at the same rate as it enters at the top. However I would suggest that the water is not flowing through every point of the sponge at the same speed... even though the entire sponge remains saturated with water. If we added some coloured water to the flow I'd expect see it to move fastest through the areas of greatest flow before it reached the edges of the sponge... this is akin to our BG and a comparison of fingertips (greater flow) to forearm (less flow).

[It Ain't Over]

A few years back I was given several arteriograms, they were taking pictures of a carotid sinus tumor on thel eft side of my neck.
At that time the dye used was very caustic. When a shot of the dye went into through the needle they has placed into my femoral artery it felt like burning acid was racing up and down from the bottom of my feet to the top of my head, including the inside of my head. That sensation went about as fast as you could sweep your hand up and down. In other words very fast. It surely did not take a minute, more like a second or two.
They used a lot milder dyes after the first couple of them, but I won't live long enough to forget that day.

[Bountyman]

Think of blood flow like the toll booth approach to the Bay Bridge. The freeway is 4 lanes and the traffic is travelling 50 mph. The entrance to the toll plaza branches into 15 toll booths where the car comes to a complete stop. If you take a view from 1000 feet at the toll plaza you see the cars that are 500 yards from the toll plaza at a steady 50 mph. After the toll plaza you see the cars at a steady 50 mph. The reason for this steady flow is the increase in the number of lanes at the toll booth. Were there just 4 toll booths the traffic would back up. The same with blood branching in the body. The slower the blood velocity, the more the arteries/veins. Although the blood slows in velocity...the volume flow remains the same.