Introduction

In this article, I will compare many parameters before and after the virtual implants to see if there are improvements. But before I would like to explain the causes of ENS because before finding solutions it is necessary to understand the problem correctly. In the second paragraph, I will define goals. What parameters do I think I can improve with these virtual implants.

In the article I will speak about different regions in the nasal cavity, to be clear here is an illustration.I
n red the anterior part which is the beginning of the nasal cavity, in green the middle meatus, it is where the middle turbinates are and finally in blue the inferior meatus where the inferior turbinates are.

Causes of ENS

The Empty Nose Syndrome can be caused by a partial or a complete cut of the inferior or middle turbinates. It can even be caused by a burn of the mucosa. The cut causes a loss of volume, that's to say an increase in emptiness and a reduction in the mucosa surface. The burn affects negatively the health of the mucosa. All of this has many effects:

• The increase in emptiness causes:
  • A modification in the distribution of the airflow, most of the airflow is redirected in the middle meatus in case of an inferior turbinectomy [1].
  • An increase in the cross-sectional area which reduces the velocity of the airflow and affects negatively the Wall Shear Stress. Less WSS means less evaporation of the mucus due to the airflow passage which leads to less cooling effect of the mucosa. Indeed the change of the mucus from the liquid state to the gaseous state leads to energy consumption which cools the mucosa. And it is this cooling that detects the TRPM8 receptors and gives us the feeling of the airflow [2]. The increase in the cross-sectional area also reduces nasal resistance.

• The reduction in the mucosa surface causes:
  • A reduction in the numbers of TRPM8 receptors simply because the receptors are in the mucosa and the fewer mucosa there are, the fewer receptors there are.
  • A reduction of the production of mucus because it is the same thing, the glands that produce mucus are found in the mucosa [3].
  • A reduction in the number of blood vessels which can decrease the temperature of the mucosa. Simply because the mucosa is kept at the right temperature thanks to the blood flow.

• The cut of turbinates disturbs the nasal cycle because a large part of the turbinates has disappeared. The nasal cycle is the phenomenon that consists of vasodilation of the turbinates on one side and then the other over a cycle of a few hours. However, it seems that the utility of the nasal cycle is still unknown [4]. But the phenomenon of vasodilatation/vasoconstriction has another very important role which is to adapt the cross-sectional area according to physical activity. Indeed during physical activity the airflow increases, in response to this, the turbinates decrease in volume via the phenomenon of vasoconstriction [5].

Goals of the virtual implants

The thing that seems not possible to do with implants is to increase the mucosa surface, an implant just moves the mucosa. In some cases, it can create a bit of a mucosa surface by stretching it but it can't be a major increase.
What it is possible to do is to decrease the emptiness, so decrease the cross-sectional area. The goal is to design the implants in order to:

• Have a better airflow distribution between the middle and the inferior meatus because it seems that this parameter has a great impact on ENS symptoms [1].
• Have a better repartition of WSS between the two regions and increase it in the region affected by the turbinectomy. Because WSS plays a major role in airflow sensation as I explained in the causes of ENS. In this study [1], the researchers found a correlation between WSS value in the lower meatus and the sensation of suffocation. “Among the 6 items in ENS6Q, complaints of “suffocation” and “nose feels too open” were significantly correlated with peak WSS in the inferior turbinate region”
  Interestingly they found no correlation between nasal resistance and ENS symptoms. “Nasal resistance did not correlate with ENS6Q or any other symptom score”.

Virtual implants placement

Virtual implants appear in red, we can say that there are 3 implants in the left nasal cavity, one on the floor, one in the nasal wall, and a small one in the septum. On right it is a pretty big implant, note that I don’t know if this implant is possible to do because it is placed behind my existing implant and the shape that I have designed is huge.
What I tried to do by designing these implants is to restore the "ideal" distance between the walls. Let me explain what I call the “ideal” distance between walls. When we see a healthy nasal cavity CT-SCAN we can see that the distance between two walls is almost the same everywhere. I measured it, it's between 1.5 and 3 mm. So I designed these implants to tend to these values without reaching them everywhere due to technical constraints. I tried to respect what could be done in terms of implantation with a big doubt about the right implant.

Change of the cross-sectional area

After the virtual implant, it is not surprising that the cross-sectional area has decreased and it is a little more regular throughout the nasal cavity.
Note that the values of the control groups are pulled from this study [6], but I measured myself some healthy CT-SCANs and I found values between 250 and 300 mm² of total cross-sectional area instead of the 200mm² in the study. So I don’t know what the normal values are. Maybe it is a range between 200 and 300 mm², I don’t know. The area also depends on body position and physical activity but I assume almost all ct-scans are done while lying down. The values obtained are therefore comparable.

Results

Streamlines

Before virtual implants

In the previous article I had not shown the right side, we can see that there is a bit better distribution of the airflow on this side.

After virtual implants

We can see that there is almost no change in the airflow distribution. Maybe in the left side view, there is a bit more streamlines in the inferior meatus. But it is not a huge improvement.

Velocity

Before virtual implants

After virtual implants

All surfaces that have an airflow velocity greater than 2.5 m/s are in red. The peak is at 3,24 m/s.
Same thing here no real improvement in velocity.

Wall Shear Stress

Before virtual implants

After virtual implants

All the walls that have a greater WSS than 0,1 Pa are in red. The peak is at around 0,9 Pa.
We can see a real change here, in the areas where the virtual implants are placed the walls are more “colored”. Which means that the WSS is higher.

In these cuts, we can clearly see that the virtual implant has increased the WSS. Now there is blue and even yellow color, which means that the WSS has increased from almost 0 Pa to values between 0,025 and 0,07 Pa.

Same thing here, there is more WSS, especially on the right side. What I can say is that it is really a positive change, concretely this improvement of the WSS should improve the feeling of the airflow in the inferior meatus. The virtual implants simply moved the walls closer to the airflow. I think it's a good strategy to adopt, identify the airflow and then bring the walls closer to the airflow in order to increase the WSS while respecting the minimum distance between the walls (1,5 - 3 mm).

Airflow humidity

Before virtual implants

After virtual implants

We can see that there is almost no change in the airflow humidity.

Airflow temperature

Before virtual implants

After virtual implants

There is a little bit less green and yellow in the last slice which means that the airflow temperature is a bit higher after the virtual implants. The temperature in the scalebar is in Kelvin so you need to subtract 273 to obtain the temperature in Celcius. And also you need to multiply by 100 before that. So for example in red the temperature is equal to 3,096*100= 309,6°K and then 309,6 - 273 = 36,6°C.

Nasal resistance and airflow symmetry

If your CFD results are in the green square you have a high probability of having normal nasal resistance and normal airflow symmetry. The resistance R is on the horizontal axis and the airflow symmetry theta (𝚹) is on the vertical axis. You can see how these indicators are calculated in this study here [7].

Airflow symmetry

Before virtual implants, the flow rate is at 7 l/min on the left and 7,3 l/min on right. This corresponds to a 𝚹 of 1,028 which is very good, the flow is almost the same in the right nasal cavity than in the left. After virtual implants, the flow rate is at 6,9 l/min on the left and 7,68 l/min on right. This corresponds to a 𝚹 of 1,097 which is a bit less good but it’s still normal according to Flowgy. So if I wanted to correct this I would have to design a smaller implant on the right or a bigger one on the left.

Nasal resistance

Nasal resistance R is calculated based on several parameters like the difference of pressure between the environment and the pharynx (delta P), the flow rate, the density of air, and the area of the nostrils. When the air passes through the nasal cavity, it undergoes a loss of pressure due to the friction on the walls, it is the delta P.
Before virtual implants, the value is 4,7 and after 6,94, it is not surprising that the value has increased because the virtual implants have decreased the cross-sectional area in certain regions of the nasal cavity.
This is rather a good thing because according to the graph the value was barely within the norm. After the implants, the values have progressed a bit in the right direction. But note that the absolute value of R is not very precise because it depends on a lot of parameters in the simulation. It's just an indicator to see if the virtual surgery has changed the value in the right direction. Also, this value seems to have no impact on the ENS symptoms as I mentioned in the “goals” paragraph. But I still think it's a good thing to be in the norm because nasal resistance is useful for normal lung function [8].

Conclusion

One of the goals was not achieved, the airflow distribution did not improve. I don't really know how to improve it, especially on the left side where it is particularly bad.
However, the virtual implants have greatly improved the WSS which is a positive thing. Also, the airflow temperature and the nasal resistance are a bit higher.
So I think that this kind of implant can be useful, especially for the airflow sensation.

References

1. Investigation of the abnormal nasal aerodynamics and trigeminal functions among empty nose syndrome patients, Chengyu Li, PhD, Alexander A. Farag, MD, Guillermo Maza, MD, Sam McGhee, Michael A. Ciccone, Bhakthi Deshpande, MA, Edmund A. Pribitkin, MD, Bradley A. Otto, MD, and Kai Zhao, PhD
2. Empty Nose Syndrome Pathophysiology: A Systematic Review, Jeanie Sozansky BS, Steven M. Houser MD,
3. Submucosal glands, Wikipedia
4. The nasal cycle in health and disease, J. Hanif
5. Sataloff's Comprehensive Textbook of Otolaryngology: Head & Neck Surgery, Robert T Sataloff, chapter 19, p 286
6. Computational fluid dynamics and trigeminal sensory examinations of empty nose syndrome patients, Chengyu Li , Alexander A Farag , James Leach , Bhakthi Deshpande, Adam Jacobowitz , Kanghyun Kim , Bradley A Otto , Kai Zhao 
7. Robust nondimensional estimators to assess the nasal airflow in health and disease, E. Sanmiguel-Rojas M. A. Burgos C. del Pino M. A. Sevilla-García F. Esteban-Ortega
8. Surgery of the turbinates and “empty nose” syndrome, Marc Oliver Scheithauer, paragraph 8