Viscosity and Poiseuille's Law (Fluid Mechanics - Lesson 10)
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- เผยแพร่เมื่อ 31 ก.ค. 2013
- A description of viscosity and Poiseuille's Law, which relates the pressure gradient along an enclosed conduit to the viscosity, length of conduit, radius of conduit, and fluid low. Several examples of its application in medicine are discussed, including rapid infusion of fluids, asthma attacks, hyperviscosity syndrome, and leukostasis.
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Thank you! Very professional and clear, your knowledge spectrum and applications are invaluable.
You deserve much much more views!
Thanks a lot for Clever Quick explanation.
thanks for this great lecture. I would like to ask that you have given a example of central catheter which have low radius and Residence was founded 21 fold increase. but flow is also proportional to delta P. if central pressure is far lower than peripheral pressure . The flow can be greater in central line (Q=P/R)
James, I wish I could help, but I'm afraid I don't quite understand your question. Are you able to clarify?
I must plead ignorance when it comes to calculating resistance once flow becomes turbulence, though I imagine it's significantly more complicated.
Just was kind of wondering how do you know when there's is to much ICP and when you do know this where and when and do you have to tap if the tap can be done ! Thanks
A question:
- you mentioned two clinical situations where the concept of viscosity was necessary to understand pathology.
- I'm curious about the effect of polycythemia and, the opposite (sort of), Anemia. Does blood viscosity increase with polycythemia? Does it decrease with (for example) aplastic anemia? If they do, Does that add any clinical reasoning to immediate or long term management?
By way of background: I read in costanzo that hematocrit was associated with viscosity, but importance was never stated.
Further, the Reynolds number is a way to predict turbulence (e.g. A heart murmur). Reynolds number being the ratio of forces from inertia to forces from viscosity--when that ratio reaches 2500 it becomes likely to get turbulence, and at 5000 it is all but certain that you'll get turbulence--knowing that turbulence (murmur) can result from anemia--everything seemed to just fall into that "aha....but wait, let me ask someone smart.." moment
Yep, the hematocrit definitely affects blood viscosity. I don't have a source off the top of my head, but it is probably the primary determinant of viscosity in patients with normal physiology (i.e. excluding leukemia and paraproteinemia). Hyperviscosity is well described in polycythemia, but perhaps unexpectantly (at least to me) is that it's best described in infants in the perinatal period: www.ncbi.nlm.nih.gov/pubmed/14631551
Since viscosity of blood impacts cardiac afterload, I've always wondered if that translates to a benefit in keeping hematocrits relatively low in patients with non-ischemic cardiomyopathy, but have never found research addressing the question.
Sorry about that I was meaning spinal fluid ! How does a clinician know when there's to much spinal pressure and when and where do they do the tap if the tap can be done and how much can be removed ! Without skull drilling !
good vids
viscosity is usually represented with the greek letter eta (looks like lower case "n").
+caliguy1260 Yeah, up until this video, I've always gone with eta. Honestly can't remember why I went with mu here. They are both used in textbooks.
+Strong Medicine
maybe because you are so used to using mu as the "micro" prefix symbol when documenting dosages. (its all greek to me anyway)
Wouldn't the small radius of peripheral veins add to the flow resistance in comparison to the much larger radii of veins that CV catheters typically access?
CV catheters are usually inserted far enough into the central veins that their tips reach the junction of the superior vena cava and the right atrium. Thus, infusions are unable to make use of the larger caliber of the vessels.
Eric's Medical Lectures The CV catheters pour into a large compartment (the right atrium) not adding to the resistance... but would not the peripheral IV catheters flow rate get impeded by the small radius of peripheral veins contributing to increased resistance? BTW, thank you for your videos... They are very helpful!!
VenusMorpheus The relatively small peripheral veins are still much larger than a single lumen of a triple lumen central venous catheter. The average diameter of the cephalic vein at the elbow (i.e. typical vein in the arm used for a large gauge IV) is about 1.9mm, and only increases in size as it merges with other veins en route to the right atrium. The typical inner diameter of a single lumen from a triple lumen central line varies between models/brands but is typically around 0.7-0.9mm. Similar to the example in the video, a two fold difference in diameter results in a huge difference in resistance.
I suppose the total length of the circuit is longer if one measures from the entry point in the antecubital fossa, as compared to the entry point of a CVC in the jugular or subclavian veins, but this difference is not nearly enough to offset the difference in diameters between the 2 options.
Eric's Medical Lectures That makes sense!! Thank You!!
what does the value of "8" signifies?
nothing it must just be a constant that arrived after integrating