# Why don't we see turbulence in the aorta even in normal situations?

I read about the Windkessel effect. Then I read about pulse pressure waves getting reflected from the periphery. If the pulse pressure wave is reflected during diastole and at the same time blood is being pumped forward by the aorta due to the Windkessel effect, then we have two opposite forces acting which should create turbulence even in a normal aorta. Why doesn't this happen?

## 2 Answers

Why don't we see turbulance in Aorta even in normal situations?

There are different parts of aorta where turbulence is possible and where not.

It is often said that in normal situations, we cannot see turbulence in aorta because aorta is very stiff and its surface is very smooth. However, this is a simplification and involves an average person (middle aged) which has stiff aortic arch too.

Note that the elasticity of arcus aortae is responsible for 50% of the volume to the peripheral circulation, thus creating a nearly continuous peripheral blood flow as anongoodnurse says, see this publication. However, not all of this blood travel to the backward direction. It would be interesting to see how much blood is travelling backward. This would help to understand what is the likely hood for turbulences.

Those models linked by Anongoodnurse's answer are a few models used to locate places of possible turbulences discretely but they do not seem to consider the amount of blood capable of creating turbulences, just discrete models:

• Stalder et al. I do not like the first publication because it is using Reynold's number that is designed originally for laminar flow. Problem with viscosity etc. There are better ways to the same thing and consider explicitly the creation of turbulence. It does much simplifications there. Fitting the equation to the physiological ranges of some set of data is bad procedure.
• Fukuda et al. I like the second publication. High velocity and turbulence and nonlinear streamlines in the ascending aorta in normal situation. In other words, high magnitude of the strain rate tensor along aortic curvatures. So we need nonlinear distribution of at least 4D (later 6D) to quantify the amount and degree of nonlinear processes in turbulences.
• Lantz et al. Third publication. Linear model for nonlinear situation. I am not convinced by their Mesh selection. Only in Mechanics' journal. Very far from Medical publication or from Mathematical. Not rigorous.

In summary, there are many models and publications to answer the question where are the turbulences. However, they try to answer nonlinear problem by linear models. I have not seen any models where they do this rigorously. I think we should narrow this problem even more, like Fukuda et al has done. They manage to provide some good pieces of information by just considering an intervention with least turbulence in the aorta.

Generally speaking, we can see some turbulence in arcus aortae in the diastole when blood bounces back from the aortic valve. The walls of arcus aortae can store about 50% of left ventricular volume. However, I do not know how much of this blood is travelling backward and reflecting back from the atrial valve and causing possibility for turbulences.

[P]ulse pressure wave getting reflected from periphery.

Pulse pressure is systolic minus diastolic pressure. Pulse wave is those small waves inside respiratory waves:

where vasomotor waves are controlling the big picture.

If the pulse pressure wave is reflected during diastole and at the same time blood is being pumped forward by aorta - -.

Wrong! Blood is pumped by heart. Aorta is just a vessel for transportation. Generally speaking, Some blood is reflected back from arcus aortae which bounches back from the aortic valve.

[Because] windkessel effect then we have two opposite forces acting which should create turbulance even in normal aorta. Why doesn't this happen?

You confuse here different terms and processes.

Generally speaking. Arcus aortae stretches during systole. It is coils back in diastole (left atrium relaxing), blood crashing off aortic valve, possibly creating a heart sound and increasing diastolic pressure. Like anongoodnurse says, in this phase, you can see some turbulence in the aorta but little, since the wall of the aorta is very smooth and only small portion of blood is travelling backward from the walls of aorta:

where see the aorta coils part.

• I wish I could agree with you here, but I don't. Furthermore, your notes aren't reflecting what you're claiming (mostly they involve the causes of the heart sounds and where they occur in the cycle seen on an EKG. The fourth Heart Sound is pathological and is caused by increased resistance to filling of the left or right ventricle because of a reduction in ventricular wall compliance, and is called the atrial gallop. Dec 27 '14 at 2:27
• Finally, the elasticity of the aorta has a lot to do with the propulsion of blood. See Elastic properties and Windkessel function of the human aorta: "the elastic forces of the aortic wall forward this 50% of the volume to the peripheral circulation, thus creating a nearly continuous peripheral blood flow." Dec 27 '14 at 2:28
• @masi I'm talking about normal individuals who do not have pathological fourth heart sound. I was referring to concept "pulse wave velocity". Now as heart pushes blood in systole, the aorta stretches, and in diastole and aorta recoils, at the same time there is the reflected pulse wave that is coming in opposite direction to that of blood propulsion due to recoil of aorta. Dec 27 '14 at 5:19
• @anongoodnurse How much of this 50% of LV is travelling backward? I have an intuition that not all of it is travelling backward so only a portion is possibly causing a turbulence. Dec 27 '14 at 8:39
• As the author states, blood flow is to the periphery, so that is clearly the major direction of the blood. I have little disagreement with your modified answer (except for some nit-picking, like your use of "atrial valve" (do you mean the aortic valve?) which makes for some lack of clarity. Your modified answer basically states what I stated in my original answer: There is some turbulence in the normal aorta. Dec 27 '14 at 18:10

There is turbulence in the normal aorta, which is thought to be one mechanism of endothelial injury leading to atherosclerosis and thrombus formation.

• I do not like the first publication because it is using Reynold's number that is desigined originally for laminar flow. Problem with viscosity etc. There are better ways to the same thing and consider explicitly the creation of turbulence. It does much simplifications there. Fitting the equation to the physiological ranges of some set of data is bad procedure. Dec 27 '14 at 8:54
• I like the second publication. High velocity and turbulence and nonlinear streamlines in the ascending aorta in normal situation. In other words, high magnitude of the strain rate tensor along aortic curvatures. So we need nonlinear distribution of at least 4D (later 6D) to quantify the amount and degree of nonlinear processes in turbulences. Dec 27 '14 at 9:03
• Third publication. Linear model for nonlinear situation. I am not convinced by their Mesh selection. Only in Mechanics' journal. Very far from Medical publication or from Mathematical. Not rigorous. Dec 27 '14 at 9:10
• @Masi - I agree with your critiques of the papers for the most part. These are three models used to study aortic turbulence. I could have included MRI studies as well, but the catheter studies are most plentiful, and they seem to agree with each other. Most of the most recent studies on turbulence in the aorta involve heart valve studies. But I think it's important to note that there is turbulence in the aorta. Dec 27 '14 at 17:54
• Yes, there is turbulence! Please, include better studies and MRI so I can review them. I am very interested in turbulence in many environments. The catheter study is mosthe beneficial in this research. MRI can describe some fluid dynamics. Dec 27 '14 at 21:26