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The difference between "Constant Flow" and "Constant Pressure"



Hello!


In the field of organ perfusion, we perfuse by pumping culture or storage fluid into a vessel.


In microfluidic experiments, the medium is pumped into the flow channel and perfused.

The actual problem with perfusion is determining which method is best:


"Constant Flow" or "Constant Pressure"?


In this article, I will discuss the differences between the constant flow and constant pressure perfusion methods.


Table of Contents;

  1. What is constant-flow perfusion?

  2. What is constant pressure perfusion?

  3. Which one is better?

  4. Summary



What is constant-flow perfusion?

Constant flow perfusion is a method that is carried out by perfusing a liquid with a constant flow rate pump. Once the flow rate of the pump is set, the flow rate is kept constant until the pump stops, making it easy to monitor the flow rate.


While the flow rate is easy to control, it is not responsive to pressure changes during perfusion.


For example, even if the sample pressure is changed and the resistance in the sample is increasing, the channel pressure will change because the flow rate is not changed.


It will result in an increase of pressure which could cause the vascular system to break.

What is constant pressure perfusion?

As the name indicates, it is a regurgitation process, in which the pressure of the flow path being pumped is kept constant. Because the pressure rate remains constant, the flow rate varies anomalously.



A common technique for constant pressure perfusion is by feeding at the height of the liquid (see the animation above).


In this case, no pumps are used, and the flow path pressure is determined by the dead weight of the perfusate in the supply bottle. As a result, it is not possible to monitor the flow rate, and therefore it is not possible to get an accurate picture of the flow rate.


Also, it needs to adjust the liquid level of the bottle to achieve constant pressure perfusion because the pressure decreases as the level of liquid falls.


On the other hand, there is a constant pressure perfusion method that is automatically controlled by connecting a pump and a pressure gauge (animation below).



Here, there is no pressure change due to the liquid level effect, and pressure and flow rate can be monitored to allow for accurate constant pressure perfusion.


Which is better?

Which perfusion is better, constant flow or constant pressure?

When you search for "constant flow perfusion" on Google scholar, about 1600 results come up.


If you look up "constant pressure perfusion," the search results are close to 1680 (author's research as of June 1, 2020, Google Scholar, https://scholar.google.co.jp ).


It seems to be dependent on what sample is being perfused. For some samples constant flow seems better while for other samples constant pressure is the preferred method.


In the field of mechanobiology, vascular endothelial cells or vascular perfusion may require precise pressure control.


Since it is not possible to accurately monitor and control the pressure in constant pressure perfusion using a liquid surface, a control system that coordinates a pressure gauge and a pump are necessary.


From my point of view as an engineer, the mechanism of constant flow is simpler than constant pressure.


As long as the flow rate of the pump is well set, no sensors or links are needed.

On the other hand, with constant pressure perfusion, a pressure gauge is needed to monitor the flow path pressure. Then you need a controller that receives and converts the signal and applies control to the pump.


Compared to constant flow perfusion, the control is much more complicated.

Those who can build such a control system by themselves are quite a perfusion maniac who also know electrical control (haha).


With our Constant Pressure Feeding Unit, you can achieve constant pressure perfusion without the technical skills of electric control or complicated controls (click here for details).


Summary

It is necessary to decide which one to choose, constant flow or constant pressure perfusion, depending on the perfusion sample.


In the field of mechanobiology, where the precise control of pressure is required, constant pressure perfusion using a pump is recommended.


Accurate constant pressure perfusion requires complex control as it is harder to operate.

Did you understand the difference between "constant flow" and "constant pressure" perfusion, a common question in perfusion culture?


TokaiHit's perfusion business offers a lineup of "Constant Pressure Feeding Units (Pat.P)" that make it easy to achieve accurate constant pressure control.


It is possible to control not only simple constant pressure but also pulsatile flow and pulsatile pressure.


Related Products

BPU

Pulsating Constant Pressure Pump BPU

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