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Pulsatile OR steady flow, which is better?

#organperfusion #cellularperfusion #beatingflow #usefulinfo


Hello,


In this article, I would like to address the one perpetual challenge that faces perfusion, which is the most suitable type of perfusion: Pulsatile or Steady-state flow?


I hope this article answers the following questions:

"What are the advantages and disadvantages of pulsatile and steady flow?"

"What is pulsating?"

"Which is better in a perfusion experiment?"


Table of Contents

  1. What is pulsatile flow?

  2. What is steady-state flow?

  3. In the field of the artificial heart

  4. The view from the vascular side

  5. How is an isolated organ?

  6. Summary


What is pulsatile flow?


Pulsatile flow is often referred to as the "flow of pulse."

But, what is the pulse? (see information from Wikipedia)


"In medicine, a pulse represents the tactile arterial palpation of the cardiac cycle (heartbeat) by trained fingertips." (Wikipedia, https://en.wikipedia.org/wiki/Pulse). According to this information, it seems to me that the flow created by that movement is called the pulsatile flow”.


What is steady-state flow?


In contrast, steady-state flow is a general method for delivering fluid at a constant rate. In this article, we often use the term "non-beating flow" to distinguish it from pulsating flow.


As you learn from experience, it is quite difficult to perform a perfect steady-state flow in isolated organ perfusion because it uses a roller pump. To achieve a steady-state flow requires a lot of effort and patience. We will explore these problems and challenges in another article.


TokaiHit offers a constant pressure feeding unit that can be used to pump fluids at constant pressure, within its product line-up.


BPU

Pulsating Constant Pressure Pump BPU

Monitoring the pressure of blood vessels during perfusion culture


For more information





In the field of the artificial (mechanical) heart.

In the history of the artificial heart, the question of whether the pump should be driven by pulsatile or steady-state flow has been debated for a long time, and continues, even today.


The first artificial heart was reported by Akutsu, Corfu, et al. in 1957, and it was using pulsatile perfusion. Since then, the pulsatile flow has been the mainstream.


In my opinion, the actual heart perfuses the system via a pulsatile mechanism. The first artificial heart was developed by mimicking this heart's pulsatile flow work mechanism.


However later, in an animal study in the United States, it was reported that: "...the animals survived for three months, even with no-beating flow (steady-state flow)."


Due to these results, people reportedly started to apply a non-pulse mechanism to artificial hearts (from the web page of National Accreditation Service accessed on June 25, 2020, http://www.ncvc.go.jp/cvdinfo/pamphlet/heart/pamph42.html# anchor-4).


Currently, both pulsatile and steady-flow are used for artificial hearts.



From the vascular side view

It is my belief that for vascular endothelial cells, the pulsatile flow approach seems to be somehow more suitable. This is because the arterial vessel is exposed to the pulsatile flow in the body environment all the time. Due to this reason, I would imagine that that the pulsatile flow has a positive effect on blood vessels.


Much investigation has been done in the field of mechanobiology, especially in vascular endothelial cells.


The keyword "endothelial pulsatile" in Google Scholar search results approximately 22,700 references (accessed June 25, 2020 Google Scholar.


https://scholar.google.co.jp/scholar?(hl=en&as_sdt=0%2C5&q=endothelial+pulsatile&btnG=).


Ando et al. suggest that "for the same strength of shear stress, the effect of pulsatile flow is generally greater than that of steady flow" in their article(Ando et al., Japanese Journal of Thrombosis and Haemostasis, Vol. 13, No. 3


https://www.jstage.jst.go.jp/article/ jjsth/13/3/13_3_3_227/_pdf).


So, from the results above, in both vascular and especially from the peripheral side, the pulsatile flow approach seems to be better.



How about in the isolated organs?


So, which perfusion is better for experiments on an isolated organ which stands in between the cell and the living organism?


It is getting more and more maniacal. Yes, the question is: What is the suitable/best perfusion for an ex-vivo organ?


To find this answer, I spent my days as a researcher at a medical university, both as a researcher and as a working graduate student, and then summarized it all in an academic paper.


The answer to this question is a bit complicated and not a straightforward one. I found that by applying a pulsatile flow from outside the organ, I was able to obtain better results than with a steady-state flow. The details of the scientific explanation and discussion will be presented in a following paper.


By applying pressure to the organs periodically from outside, it stimulates the pulsatile flow on the arteries’ vessels and entire organs perfused effectively, which went on to survive for a long period of time.


Related article:

"Ex-vivo organ perfusion": application to muscular and skeletal studies

(14 days of long-term perfusion)



Academic article:

Intermittent application of external positive pressure helps to preserve organ viability during ex vivo perfusion and culture.





Of course, to achieve such results, it took a lot of trial and error, especially the improvement and experimentation of the devices. Please read more about experiment achievement in another article if you are interested.


Conclusion:

Mildly pulsatile and pressurized are efficient for organ perfusion.



Summary

The grand debate of "whether the pulsating or steady flow is better" is covered in this article.

To summarize:

  • The artificial heart has both pulsatile and steady flow.

  • From a vascular point of view, the pulsatile flow looks better.

  • Mild pulsatile pressurization to the isolated organ will assist in keeping the condition and function much better than only pulsatile or steady-state flow.

What did you think?


The question of the perpetual challenge for perfusion, “which is the suitable perfusion method, Pulsatile or Steady-state flow” is still inconclusive.


We hope that this article will be of some help to those who are researching this field.


BPU

Pulsating Constant Pressure Pump BPU

Monitoring the pressure of blood vessels during the perfusion culture


For more information