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

The actual problem with the perfusion is

"Constant Flow" or "Constant Pressure"?

In this article, I will discuss the differences between 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?



It is a method of perfusing a liquid with a constant flow rate pump. Once the flow rate of the pump is set, the flow rate 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 results in the pressure keeps an increase in the vascular system may break.

What is constant pressure perfusion?


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



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

In this case, no pumps are used, and the flow path pressure 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 at decreases as the liquid level 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.

Constant Pressure Feeding Unit

The OCS-BPU Pat.P (Constant Pressure Perfusion and Pressure Monitoring) system with a reusable mechanism

Click here to download the catalog.

Click here for an approximate price.


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 better to use a constant flow or constant pressure, depending on the sample to perfuse.



The field of mechanobiology, such as 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, in this case, a control system that coordinates a pressure gauge and a pump are necessary.

Besides, 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 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 knows 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


Between constant-flow and constant-pressure perfusion, it is necessary to decide which one to choose, depending on the perfusion sample.

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

Accurate constant pressure perfusion requires complex control.

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.


Products introduced

Constant Pressure Feeding Unit

The OCS-BPU Pat.P (Constant Pressure Perfusion and Pressure Monitoring) system with a reusable mechanism

Click here to download the catalog.

Click here for an approximate price.



Author: Kazunori Sano, Ph.D


#usefulinfo #perfusion