Does blood vessel constriction cause increased blood velocity and pressure, and decreased flow?

[irishking33]

I'm trying to see if I understand this correctly:

1. Vasoconstriction of blood vessels (both arteries and veins) causes INCREASED blood pressure in them, INCREASED blood velocity, and DECREASED blood flow.
2. Vasodilation of blood vessels (both arteries and veins) causes DECREASED blood pressure in them, DECREASED blood velocity and INCREASED blood flow.

Do I have this correct?

---

Members don't see this ad.

 

[sovereign0]

I'm trying to see if I understand this correctly:

1. Vasoconstriction of blood vessels (both arteries and veins) causes INCREASED blood pressure in them, INCREASED blood velocity, and DECREASED blood flow.
2. Vasodilation of blood vessels (both arteries and veins) causes DECREASED blood pressure in them, DECREASED blood velocity and INCREASED blood flow.

Do I have this correct?

 

[CherryRedDracul]

View attachment 279720

Additionally, remember that flow = cross-sectional area x velocity.

So, for example, if vasodilation results in a quadrupling of the cross-sectional area of vessels, but halves the velocity, then you've increased flow by 2x.

 

[Radetzky]

No vasoconstriction causes the pressure in the affected vessel to fall

 

[nimbus]

No vasoconstriction causes the pressure in the affected vessel to fall

Find a volunteer, start an arterial line, give a bolus of phenylephrine, and get back to us on that.

 

[emmajones]

Blood flow is the movement of blood through a vessel, tissue, or organ. ... In the arterial system, as resistance increases, blood pressure increases and flow decreases. In the venous system, constriction increases blood pressure as it does in arteries; the increasing pressure helps to return blood to the heart.

If you want more information in-depth, you can get several medical writing blogs over the net.

 

[Thesimplelifeofamyloid]

I believe there's two different equations you want to look at there. The principle you want to remember is that the body is always trying to keep flow constant (steady state). In general, you can think of this in terms of the formula Q= AV and Q = P/R. Let's consider what happens to VELOCITY first. First and foremost, vasoconstriction would result in a decrease in cross-sectional area, resulting in an increase in blood velocity. Vasodilation would result in a increase in cross sectional area, and decreased velocity. Again, when the body is in STEADY STATE, it tries to keep flow constant. Now lets look at PRESSURE. In regards to pressure, we want to look at Q = P/R. By vasoconstricting you are essentially increasing the resistance to flow. In order to keep flow constant, you would see an increase in pressure. The opposite goes for vasodilation. Again, the body always wants to keep flow CONSTANT. If it doesn't, then there's something pathological at play.

 

[Radetzky]

Find a volunteer, start an arterial line, give a bolus of phenylephrine, and get back to us on that.

I'm aware of how vasoconstrictors work and what's happening here is an increase in TPR. However if you're talking about vasoconstricting a single vessel, the pressure WITHIN THAT SEGMENT of vessel will fall as resistance and velocity increase.

 

[nimbus]

I'm aware of how vasoconstrictors work and what's happening here is an increase in TPR. However if you're talking about vasoconstricting a single vessel, the pressure WITHIN THAT SEGMENT of vessel will fall as resistance and velocity increase.

Effect of vasodilation and vasoconstriction on microvascular pressures in skeletal muscle - PubMed

The effect of topically applied papaverine (PAP) and norepinephrine (NE), on the microvascular pressure distribution was studied in the cremaster muscle of anesthetized rats. The cremaster muscle was exteriorized into a tissue bath containing Krebs bicarbonate buffer, and microvessel diameters...

www.ncbi.nlm.nih.gov

 

[Radetzky]

Effect of vasodilation and vasoconstriction on microvascular pressures in skeletal muscle - PubMed

The effect of topically applied papaverine (PAP) and norepinephrine (NE), on the microvascular pressure distribution was studied in the cremaster muscle of anesthetized rats. The cremaster muscle was exteriorized into a tissue bath containing Krebs bicarbonate buffer, and microvessel diameters...

www.ncbi.nlm.nih.gov

Ok guess I might be wrong. You'll note however that that venous pressure does fall. NE significantly constructs venules too, so where is the pressure drop occurring then?

 

[nimbus]

Ok guess I might be wrong. You'll note however that that venous pressure does fall. NE significantly constructs venules too, so where is the pressure drop occurring then?

It’s probably a function of flow. Remember the arterioles and venules are in series with venules distal to the arterioles.

 

[LucidSplash]

#BasisOfVascularSurgery

 

[Radetzky]

It’s probably a function of flow. Remember the arterioles and venules are in series with venules distal to the arterioles.

Well actually we know that the pressure drop occurs prior to the capillary. So while the pressure within the constricted segment is now higher at the proximal portion, does it not logically follow that at some point further along the constricted segment the pressure becomes lower than it was before?