Freethought & Rationalism Archive

Vanderzyden · 11-09-2002, 07:44 PM

Folks,

Surely you will understand if I grow weary of this discussion. I have made many points here--many of them several times--but they have been ignored or dismissed. I have already provided my rationale for the internals of the CV system. As far as I can tell, I have made only one error, and that was previously acknowledged. As such, I expect that I will limit the length of subsequent posts and simply refer people to the earlier part of the thread. If the reader (e.g. Rufus) refuses to go back and read, then they will just have to think (unjustifiably) that their point of view is correct. I will not worry about convincing those who harbor such dispositions.

Some clarifications:

1. Yes, gravity has no direct effect on the pump in a closed system. However, gravity still produces hydrostatic pressure in the vertical runs of either the influent or effluent. (Note: this was one element of information missing in the "pumping from the lake bed" example).

2. Similarly, gravity will significantly affect the non-horizontal (upright or inverted) fetal CV circulation. Since I have shown that the buoyancy effects are negligible for a third-trimester fetus, it would seem that gravity must be taken into account when consider the corresponding hydrostatic effects (that develop primarily in the vena cava and the aorta). Therefore, correct placement of the influent and effluent (umbilical vein and arteries) will be crucial.This has been discussed at length previously, with no discernible refutation forthcoming.

In general, when we consider fluid statics alone, it seems that we may compare the fetal and adult CV systems and see that gravity will be significant.

Quote:

It important to understand how posture affects vascular volumes and pressures. When a person in lying down, there is virtually no hydrostatic pressure difference between the level of the heart and feet. The mean aortic pressure may be 95 mmHg, capillary pressure in the feet may be about 20 mmHg, and central venous pressure near the right atrium may be near 0 mmHg. When the person stands upright, assuming no baroreceptor or myogenic reflexes operating, the mean aortic and central venous pressures will fall. A hydrostatic column equal to the vertical distance from the heart to the feet will increase capillary pressure in the feet. If the distance from the heart to the feet is 120 cm, then the hydrostatic pressure exerted on the capillaries in the feet will be 120 cmH20, which is the equivalent of 88 mmHg (mercury is 13.6-times more dense than water). This hydrostatic pressure added to the normal capillary pressure, will increase the capillary pressure in the feet to 108 mmHg! Without the operation of important compensatory mechanism, this would lead to significant edema in the feet and dependent limbs.

In this model, mean aortic pressure (MAP) and central venous pressure (CVP) are shown as reservoirs. The vertical height between these two reservoirs represents the systemic perfusion pressure. Cardiac output (CO) constantly refills the aortic reservoir as it empties into the systemic circulation. In a horizontal configuration (Panel A), capillary pressure (PC) will be some value between MAP and CVP, typically about 20 mmHg. If the horizontal tube (i.e., the vasculature) is orientated vertically (Panel B), PC will increase because of hydrostatic forces. If the vasculature were rigid as diagramed in Panel B, then there would be no volume shifts and MAP and CVP would remain unchanged (CO would also remain unchanged). However, if the vasculature were highly compliant (as it actually is), then the increased hydrostatic forces will increase transmural pressure across the vessel walls (transmural pressure is inside minus outside pressure) and expand the vessels (Panel C). The blood for this vascular expansion would come from the venous (predominately) and arterial reservoirs, thereby decreasing CVP and MAP. The decrease in CVP would decrease cardiac preload and decrease CO by the Frank-Starling mechanism. The decreased CO will result in a fall in MAP (decreased reservoir height). The net effect would be reductions in both MAP and CVP, although quantitatively, the fall in MAP will be 10-20 times greater than the fall in CVP because of the relative compliances of arterial and venous vessels.

-- from "Effects of Gravity on Venous Return":

<a href="http://www.oucom.ohiou.edu/cvphysiology/CF017.htm" target="_blank">http://www.oucom.ohiou.edu/cvphysiology/CF017.htm</a>

Venous return (VR) is the flow of blood back to the heart. Under steady-state conditions, venous return must equal cardiac output (CO) when averaged over time because the cardiovascular system is essentially a closed loop (see figure at right). Otherwise, blood will accumulate in either the systemic or pulmonary circulations. Although cardiac output and venous return are interdependent, each can be independently regulated. A change in either cardiac output or venous return will affect the other at steady-state because the cardiovascular system is closed. In reality, the circulatory system is made up of two circulations (pulmonary and systemic) situated in-series between the right ventricle (RV) and left ventricle (LV) as depicted in the figure to the right.

-- from "Venous Return - Hemodynamics":

<a href="http://cvphysiology.com/Cardiac%20Function/CF016.htm" target="_blank">http://cvphysiology.com/Cardiac%20Function/CF016.htm</a>

Also, you can go here to survey many intelligently designed aspects of cardiovascular physiology, such as compensatory attributes (e.g. vascular constriction and dilation).

<a href="http://cvphysiology.com/table_of_contents%20-%20discipline.htm#Hemodynamics" target="_blank">http://cvphysiology.com/table_of_contents%20-%20discipline.htm#Hemodynamics</a>

Final note: As some readers will surmise from the above excerpts (and the website), the fluid mechanical picture is far more complex than I am discussing here. I do not take it further because the other effects are important but not critical. What I have contributed (or relayed) is more than sufficient.

Good night,

John

[ November 09, 2002: Message edited by: Vanderzyden ]

Asha'man · 11-09-2002, 08:02 PM

Quote:

Originally posted by Vanderzyden:
Something else to consider: skin is tough; even fetal skin. It is not comparable to, say, celophane. Also, only a small volume of blood reaches the surface of the skin, where its pressure would interact with external hydrostatic pressure. Most of the blood volume is well inside. The calculations are complex, since we would need to analyze the interaction of skin with the external fluid (water/amniotic fluid) to obtain the net pressure force that can be transmitted to the capillaries within the skin.

Again, Vanderzyden is simply wrong. He may be reading some interesting physics books, but is unable to apply that reading to a real world situation.

External hydrostatic pressure affects the entire body, not just the outer skin. As a scuba diver, I have personally been to a depth of 130 feet, and subject to a pressure of 5 atmospheres (somewhere around 200 PSI). Those 5 atmospheres compressed my entire body, from the outermost skin to the innermost organs. Every portion of my body was squeezed equally, and in such perfect balance that I was unable to feel any squeeze at all. If the pressure had been applied only to the surface of my skin, severe damage to the skin would clearly be the result.

As further proof that external hydrostatic pressure is applied to the entire system, consider the entire problem of decompression and scuba diving. If the interior was not subject to the increased pressure of depth, then there would be no need to worry about decompression when rising to the surface. Failing to take this pressure into account is a fatal mistake, and any quick search of diving medicine will show ample evidence of this. Rapid decompression can and will form bubbles within each and every body tissue, including bones.

<img src="graemlins/banghead.gif" border="0" alt="[Bang Head]" /> <img src="graemlins/banghead.gif" border="0" alt="[Bang Head]" />

Vanderzyden · 11-09-2002, 08:07 PM

Ashamann,

In general, it would seem that you are incorrect. For example, you are overlooking the fact that you have a rib cage, thick abdominal muscles, and that one of those "atmospheres" is already experienced before you dive below the surface. Rather than go into full detail, let me simply help with this correction:

5 [atm] = 5 * 14.7 [psi] = 73.5 [lb/in2]

Note: [psi] = [lb/in2] = pounds of force per square inch]

I should think you would know this intuitively if you were an experienced diver.

John

[ November 09, 2002: Message edited by: Vanderzyden ]

RufusAtticus · 11-09-2002, 08:12 PM

Vander,

You are still making the same mistakes you did pages ago. You can't use references to gravity's effect on adult circulation to prove something about fetal circulation. Why? Air has a different density than amniotic fluid.

Furthermore, you have yet to calculate the significance that gravity has on fetal circulation. Your calculations, assuming they are right, show that external pressure due to gravity is insignificant, but you haven't done any calculations to show that internal pressure do to gravity is significant. Your claim is that internal pressure due to gravity is significant, but where are your calculations for this? The only calculations I see are for external pressure. Show us the math!

You keep insisting that I have missed something you have said. Well this thread is 15 pages long. Please either repost whatever your are refering to or tell me what page it is on. If I have truely missed what you said, then it should be extremely easy for you to tell me where it is.

~~RvFvS~~
P.S. Since you haven't been back to the Good Mutation thread, have you conceded that they exist?

[ November 09, 2002: Message edited by: RufusAtticus ]

Asha'man · 11-09-2002, 08:20 PM

Quote:

Originally posted by Vanderzyden:
 2. Similarly, gravity will significantly affect the non-horizontal (upright or inverted) fetal CV circulation. Since I have shown that the buoyancy effects are negligible for a third-trimester fetus, it would seem that gravity must be taken into account when consider the corresponding hydrostatic effects (that develop primarily in the vena cava and the aorta). Therefore, correct placement of the influent and effluent (umbilical vein and arteries) will be crucial.This has been discussed at length previously, with no discernible refutation forthcoming.

Repeating the same mistake does not make it any less incorrect the second time around. Buoyancy effects are not negligible for a third-trimester fetus.

Since you apparently ignored my point the first time, let me repeat myself:

Quote:

Buoyancy is completely unaffected by the size of the container. An object that will float in a 100 gallon water tank will not suddenly sink when placed in a 10 gallon water tank.

If an object displaces 5lbs of water, then it will have 5lbs of buoyant lift. Period. The relative size of the container vs the object is completely irrelevant!

As the fetus grows, the effect of buoyancy increases in direct proportion to the displacement of the fetus.

Buoyancy is not affected by the proximity of the container wall. (A neutrally buoyant diver does not suddenly sink when he approaches the wall of a swimming pool!) The total volume of the water is irrelevant. The only important value is the volume of water displaced. Since the density of a growing fetus is more or less constant, the volume of water displaced will be more or less exactly the same as the fetus� weight. As the fetus grows, it�s displacement increases accordingly, and therefore so does the buoyancy.

<img src="graemlins/banghead.gif" border="0" alt="[Bang Head]" />

Asha'man · 11-09-2002, 08:49 PM

Quote:

Originally posted by Vanderzyden:
Ashamann,

Please learn how to type my name correctly. It isn�t that hard, and cut&paste isn�t that hard to do either. If you are doing it deliberately, I see no reason to stoop to such childish behavior.

Quote:

Originally posted by Vanderzyden:
In general, it would seem that you are incorrect. For example, you are overlooking the fact that you have a rib cage, thick abdominal muscles, and that one of those "atmospheres" is already experienced before you dive below the surface. Rather than go into full detail, let me simply help with this correction:

5 [atm] = 5 * 14.7 [psi] = 73.5 [lb/in2]

Note: [psi] = [lb/in2] = pounds of force per square inch]

(Sorry, it�s late, and I typed the wrong number into my calculator when punching up the psi value: you are correct in your value of 73.5, I was in error.)

However, if you think that my rib cage and abdominal muscles are able to withstand an increase in pressure of 4 atmospheres, then you are sorely mistaken. I am not superman, and don�t have abs of steel. Grabbing a ruler off my desk, I quickly measure a section of my massively muscular abdomen as 10� by 5�, or 50 square inches. Applying the value of 73.5 [lb/in2] to that section of skin, and you will find a force of 3,675lbs. According to your model, this will be opposed by a single internal atmosphere of pressure, or 14.7 * 50 = 735lbs.

Apparently, you think my thick abs are capable of supporting the remaining force of 2,940lbs. I appreciate the compliment, but would rather hear one that is at least believable.

Quote:

Originally posted by Vanderzyden:
I should think you would know this intuitively if you were an experienced diver.

The fact that I am an experienced diver and still alive points to the fact that I understand how this pressure affects my body more than you do.

And you completely ignored my other evidence: the fact that scuba decompression injuries can and will form bubbles in internal tissues of the body.

Happy Wonderer · 11-09-2002, 09:43 PM

Quote:

Originally posted by Asha'man:

However, if you think that my rib cage and abdominal muscles are able to withstand an increase in pressure of 4 atmospheres, then you are sorely mistaken. I am not superman, and don�t have abs of steel. Grabbing a ruler off my desk, I quickly measure a section of my massively muscular abdomen as 10� by 5�, or 50 square inches. Applying the value of 73.5 [lb/in2] to that section of skin, and you will find a force of 3,675lbs. According to your model, this will be opposed by a single internal atmosphere of pressure, or 14.7 * 50 = 735lbs.

I think that Vanderzyden will claim that I can "rest assured that he is perfectly aware of this..." but it really seems that he doesn't understand that PSI is pounds per square inch. This is illustrated by his incredulity that immersion in a pool could have any effect on circulation other than a small one that can be "safely ignored."

When you see the word per, think multiply. If I talk about "miles per hour", and want to figure the total miles gone in 2 hours, I multiply the "miles per hour" by the number of hours. If I talk about "pounds per square inch" and want to figure the total pressure on a system that is 200 square inches, I multiply the PSI (pounds per square inch) by 200.

Just wanted to make it perfectly clear why Asha'man is multiplying by the surface area of his abs to get the total pressure exerted. It is exactly the same reason that the "15 pounds" pressure in the swimming pool was not an incorrect statement.

Hope this helps.

HW

Dr Rick · 11-09-2002, 11:49 PM

Quote:

Originally posted by Vanderzyden:
Surely you will understand if I grow weary of this discussion.

Those self-inflicted wounds really hurt after a while

Quote:

I have made many points here--many of them several times--but they have been ignored or dismissed.

I think repeating myself is a great substitute for knowledge, reasoning, and honesty; why is it you guys don't believe what I say after I've said it over and over?

Quote:

I have already provided my rationale for the internals of the CV system.

Trust me, I really have.

Quote:

As far as I can tell, I have made only one error, and that was previously acknowledged.

Let's see, now: I was wrong about gravity, hydrostatic pressure, the thorax, heart valves, blood pressure, ligaments, oxygenation, and the liver. Yup, all that's only one error.

Quote:

As such, I expect that I will limit the length of subsequent posts

There is a god.

Quote:

If the reader refuses to go back and read, then they will just have to think (unjustifiably) that their point of view is correct.

Try it; it always works for me.

Quote:

What I have contributed (or relayed) is more than sufficient.

...to demonstrate my ignorance.

[ November 10, 2002: Message edited by: rbochnermd ]

[ November 10, 2002: Message edited by: scigirl ]

Adrian Selby · 11-09-2002, 11:52 PM

This is a most fascinating thread. I do wonder if you did just ban Vanderzyden for being stubbornly and insultingly wrong it wouldn't be a bad thing, after all, if anyone wanted to check out for themselves whether it was justified surely you have all the evidence you'd need.

That aside, as it is a personal comment only, why does it seem that any 15 page thread in this section is a load of people against Vanderzyden, I knew it before I started reading, having read previous threads here.

Perhaps what would be better would be some form of formal debate, as he seems to thrive on weaving out of multiple points from numerous suitably outraged scholars of subjects he's pronouncing on. I daresay he'd turn down the offer of a debate, but perhaps when another thread starts with his posts on it, we could allow a single poster to go about it in a way that doesn't muddy up the progress of exchange-riposte that is so clear with only two debaters.

Jesus Tap-Dancin' Christ · 11-09-2002, 11:54 PM

Vander, how self-blind are you?

You make the same points again and again, with little to no support, your support is then utterly eroded, counter-points are made---and you repeat yourself. After your points have been refuted.

I'm surprised people still respond to you. You really are a waste of time.

11-09-2002, 08:07 PM	#363
Vanderzyden Senior Member Join Date: Jul 2002 Location: California Posts: 694	Ashamann, In general, it would seem that you are incorrect. For example, you are overlooking the fact that you have a rib cage, thick abdominal muscles, and that one of those "atmospheres" is already experienced before you dive below the surface. Rather than go into full detail, let me simply help with this correction: 5 [atm] = 5 * 14.7 [psi] = 73.5 [lb/in2] Note: [psi] = [lb/in2] = pounds of force per square inch] I should think you would know this intuitively if you were an experienced diver. John [ November 09, 2002: Message edited by: Vanderzyden ]</p>

11-09-2002, 08:12 PM	#364
RufusAtticus Veteran Member Join Date: Nov 2001 Location: NCSU Posts: 5,853	Vander, You are still making the same mistakes you did pages ago. You can't use references to gravity's effect on adult circulation to prove something about fetal circulation. Why? Air has a different density than amniotic fluid. Furthermore, you have yet to calculate the significance that gravity has on fetal circulation. Your calculations, assuming they are right, show that external pressure due to gravity is insignificant, but you haven't done any calculations to show that internal pressure do to gravity is significant. Your claim is that internal pressure due to gravity is significant, but where are your calculations for this? The only calculations I see are for external pressure. Show us the math! You keep insisting that I have missed something you have said. Well this thread is 15 pages long. Please either repost whatever your are refering to or tell me what page it is on. If I have truely missed what you said, then it should be extremely easy for you to tell me where it is. ~~RvFvS~~ P.S. Since you haven't been back to the Good Mutation thread, have you conceded that they exist? [ November 09, 2002: Message edited by: RufusAtticus ]</p>

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11-09-2002, 11:52 PM	#369
Adrian Selby Senior Member Join Date: Jan 2002 Location: Farnham, UK Posts: 859	This is a most fascinating thread. I do wonder if you did just ban Vanderzyden for being stubbornly and insultingly wrong it wouldn't be a bad thing, after all, if anyone wanted to check out for themselves whether it was justified surely you have all the evidence you'd need. That aside, as it is a personal comment only, why does it seem that any 15 page thread in this section is a load of people against Vanderzyden, I knew it before I started reading, having read previous threads here. Perhaps what would be better would be some form of formal debate, as he seems to thrive on weaving out of multiple points from numerous suitably outraged scholars of subjects he's pronouncing on. I daresay he'd turn down the offer of a debate, but perhaps when another thread starts with his posts on it, we could allow a single poster to go about it in a way that doesn't muddy up the progress of exchange-riposte that is so clear with only two debaters.

11-09-2002, 11:54 PM	#370
Jesus Tap-Dancin' Christ Veteran Member Join Date: Apr 2001 Location: Heaven Posts: 6,980	Vander, how self-blind are you? You make the same points again and again, with little to no support, your support is then utterly eroded, counter-points are made---and you repeat yourself. After your points have been refuted. I'm surprised people still respond to you. You really are a waste of time.

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