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Mass flux

0.02

Re = 2,500

Pressure loss

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Fig. 19.1 Pressure loss over mass ux; Reynolds numbers indicating turbulent conditions

0.015

0.01

0.005

−0.005

−0.01

Re = 1,170

Unsteady medium Bezier

Start

inspiration

Re = 400

Re = 790

Start

expiration

R. Mösges

Unsteady

Steady

Re = 1,170

Re = 1,000

Re = 500

−0.015

−0.02

−0.1 −0.08 −0.06−0.04 −0.02 0 0.02 0.04 0.06 0.08 0.1 0.12

Re = 1,980

Expiration Inspiration

require a multidimensional representation of ow in space and time. In comparison to 2D or perspective representations, virtual realitybased visualization, i.e., stereoscopic and usercentered projection techniques, allows a much more intuitive comprehension of spatiotemporal correlations. In contrast to animation techniques, virtual reality is inherently interactive and thus allows an interactive exploration of simulation data.

In the context of the project, we are employing different visualization techniques tailored to the needs of the potential users. For the validation of the numerical simulation, we implemented standard visualization techniques like cut planes, isosurfaces, streamlines, and stream ribbons, all primarily based on the visualization toolkit. For the physicians, tailored visualization techniques are still to be determined and to be studied. The added dimensions in the visualization lead to the necessity of a user interface that enables the user to concentrate on the exploration and evaluation of the simulation data via dedicated navigation techniques, speech recognition, and advanced interaction methods for applying the visualization methods. The feedback of users shows that the multimodal user interface supports the visual validation process of the numerical simulation in such a way that the simulation results can be explored in an intuitive manner.

19.3 Application

19.3.1 Nasal Cavity 3D ImagingBased Modeling: AnAssessment Tool fortheAnti-Obstructive Potency ofAntiallergic Compounds

It was the objective of this study to visualize the anti-obstructive effect of intranasal steroid sprays (INS) in a patient with allergic rhinitis by simulating the nasal airow with computational uid dynamics. The patient underwent magnetic resonance imaging (MRI). After nasal allergen challenge, all measurements were repeated 30 min later. During the following 2weeks, the test subject applied the INS.Then again MRI was performed before and 30min after allergen challenge.

Figure 19.2 compares the nasal ow before and after allergen challenge at baseline. Before allergen exposure, a pattern of widespread ow distribution over the entire nasal cavity can be noticed (left). After exposure to the allergen, ow to the more cranial parts of the nasal cavity becomes sparse (right).

Figure 19.3 shows the ow patterns in the nasal cavity calculated from the MRI-based model after 14days of (prophylactic) treatment with an intranasal steroid. Again, the distribution

19 Computational Fluid Dynamics oftheNasal Cavity

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Fig. 19.2 Nasal airow at baseline before (left) and after (right) allergen challenge

Fig. 19.3 Nasal airow after 2weeks of treatment with an intranasal steroid before (left) and after (right) allergen

challenge

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Fig. 19.4 Nasal airow at baseline after allergen challenge

of airow at baseline is widespread over the entire nasal cavity. Velocity of airow is somewhat reduced after allergen challenge, however, by far not as pronounced as before treatment. We therefore conclude that this demonstrates the anti-obstructive effect of the intranasal steroid.

Similar improvements could be demonstrated for the treatment with an anti-obstructive antihistamine comparing the ow pattern at baseline (Fig.19.4) with the ow pattern after 5weeks of treatment (Fig.19.5).

Fig. 19.5 Nasal airow after 5weeks of antihistamine treatment after allergen challenge

19.4 Conclusion

Leong and colleagues have pointed out the potential benets of CFD technology applied to rhinology in their systematic review saying that “this technology has improved understanding of the complex nasal anatomy and the implications of disease and surgery on physiology” [2]. We can only partially support this viewpoint. Nasal ow simulation primarily has served to demonstrate physiologic and patho-

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logical ow patterns in the nasal cavity. It has been used in individual cases for preoperative planning and for the assessment of outcomes in rhinosurgery. The origins of this method date back to the 1980s. Research has been ongoing in this eld for more than 20 years without establishing the method in regular care. This is due to the fact that standards are still lacking and consensus on the interpretation of the ndings and on reliable outcome parameters has not been reached. CFD technology can be a valuable but extremely complex and by consequence costly research tool for sophisticated problems like drug distribution in the nasal cavity or the visualization of drug effects on the nasal mucosa. There is, however, hope that these limitations will be overcome in future with further improvements in imaging and software technology.

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5. Tan J, et al. Numerical simulation of normal nasal cavity airow in Chinese adult: a computational ow dynamics model. Eur Arch Otorhinolaryngol. 2012;269(3):881–9.

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8. Chen XB, etal. Impact of inferior turbinate hypertrophy on the aerodynamic pattern and physiological functions of the turbulent airow—a CFD simulation model. Rhinology. 2010;48(2):163–8.

9. Chen XB, etal. Assessments of nasal bone fracture effects on nasal airow: a computational uid dynamics study. Am J Rhinol Allergy. 2011;25(1):e39–43.

10. Garcia GJ, et al. Septal deviation and nasal resistance: an investigation using virtual surgery and computational uid dynamics. Am J Rhinol Allergy. 2010;24(1):e46–53.

11. Guo Y, etal. A computational uid dynamics study of inner ow through nasal cavity with unilateral hypertrophic inferior turbinate. Lin Chung Er Bi Yan Hou Tou Jing Wai Ke Za Zhi. 2009;23(17):773–7.

12. Lee HP, et al. Changes of airflow pattern in inferior turbinate hypertrophy: a computational fluid dynamics model. Am J Rhinol Allergy. 2009;23(2):153–8.

13. Lee HP, et al. Effects of septal perforation on nasal airow: computer simulation study. J Laryngol Otol. 2010;124(1):48–54.

14. Liu T, etal. Effects of septal deviation on the airow characteristics: using computational uid dynamics models. Acta Otolaryngol. 2012;132(3):290–8.

15. Sun XZ, et al. Analysis of the character of selfadaptation of nasal structure in patients with nasal septum deviation. Zhonghua Er Bi Yan Hou Tou Jing Wai Ke Za Zhi. 2008;43(5):351–4.

16. Zhu JH, etal. Inspirational airow patterns in deviated noses: a numerical study. Comput Methods Biomech Biomed Engin. 2013;16(12):1298–306. https://doi.

org/10.1080/10255842.2012.670850.

17. Bockholt U, etal. Rhinosurgical therapy planning via endonasal airow simulation. Comput Aided Surg. 2000;5(3):175–9.

18. Iwasaki T, etal. Improvement of nasal airway ventilation after rapid maxillary expansion evaluated with computational uid dynamics. Am J Orthod Dentofac Orthop. 2012;141(3):269–78.

19. Ozlugedik S, etal. Numerical study of the aerodynamic effects of septoplasty and partial lateral turbinectomy. Laryngoscope. 2008;118(2):330–4.

20. Wexler D, Segal R, Kimbell J. Aerodynamic effects of inferior turbinate reduction: computational uid dynamics simulation. Arch Otolaryngol Head Neck Surg. 2005;131(12):1102–7.

21. Xiong GX, etal. Computational uid dynamics simulation of airow in the normal nasal cavity and paranasal sinuses. Am J Rhinol. 2008;22(5):477–82.

22. Chen XB, et al. Drug delivery in the nasal cavity after functional endoscopic sinus surgery: a computational uid dynamics study. J Laryngol Otol. 2012;126(5):487–94.

23. Frank DO, etal. Computed intranasal spray penetration: comparisons before and after nasal surgery. Int Forum Allergy Rhinol. 2013;3(1):48–55.

24. Garlapati RR, etal. Indicators for the correct usage of intranasal medications: a computational uid dynamics study. Laryngoscope. 2009;119(10):1975–82.

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26. Pless D, et al. Numerical simulation of air temperature and airow patterns in the human nose

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during expiration. Clin Otolaryngol Allied Sci. 2004;29(6):642–7.

27. Sommer F, Kroger R, Lindemann J.Numerical simulation of humidication and heating during inspiration within an adult nose. Rhinology. 2012;50(2):157–64.

28. Ishikawa S, et al. Flow mechanisms in the human olfactory groove: numerical simulation of nasal physiological respiration during inspiration, expiration, and snifng. Arch Otolaryngol Head Neck Surg. 2009;135(2):156–62.

29. Sung SJ, etal. Customized three-dimensional computational uid dynamics simulation of the upper airway of obstructive sleep apnea. Angle Orthod. 2006;76(5):791–9.

30. Xu C, et al. Computational uid dynamics modeling of the upper airway of children with obstructive sleep apnea syndrome in steady ow. J Biomech. 2006;39(11):2043–54.

31. Prinsell JR. Maxillomandibular advancement surgery for obstructive sleep apnea syndrome. J Am Dent Assoc. 2002;133(11):1489–97; quiz 1539–40

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maxillomandibular advancement. J Craniofac Surg. 2009;20(2):426–30.

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34. Lorensen WE, Cline HE. Marching cubes: a high resolution 3D surface construction algorithm. ACM Siggraph Comput Graph. 1987;21(4):163–9.

35. Taubin G, Zhang T, Golub G.Optimal surface smoothing as lter design. In: Computer vision—ECCV’96. Berlin: Springer; 1996. p.283–92.

36. Eitel G, etal. Numerical simulation of nasal cavity ow based on a lattice-Boltzmann method. In: New results in numerical and experimental uid mechanics VII.Berlin: Springer; 2010. p.513–20.

37. Wheeler SM, Corey JP. Evaluation of upper airway obstruction—an ENT perspective. Pulm Pharmacol Ther. 2008;21(3):433–41.

38. Bouzidi M, Firdaouss M, Lallemand P. Momentum transfer of a Boltzmann-lattice uid with boundaries. Phys Fluids. 2001;13:3452.

39. Finck M, Hänel D, Wlokas I.Simulation of nasal ow by lattice Boltzmann methods. Comput Biol Med. 2007;37(6):739–49.

Physiology andPathophysiology

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ofNasal Breathing

AchimG.Beule, GiorgiGogniashvili, andGunterH.Mlynski

Core Messages

• Normal respiratory function in the nose requires low physiological nasal airow resistance as well as adequate contact between the air and a large mucosal surface in a slit-shaped ow channel.

• Narrowing of the nasal airways and/or severe turbulence can cause a pathological rise in nasal resistance.

• Since resistance to ow rises exponentially with increasing stenosis, even slight narrowing in the area of the isthmus can lead to severe nasal obstruction. This fact is often overlooked.

• In terms of respiratory function, the nasal ow channel can be divided into an inow area, a functional area, and an outow area.

• In the inspiratory ow direction, the inow area consists of the vestibulum, the isthmus, and the anterior cavum. After passing over the

A. G. Beule (*) Department of Otorhinolaryngology, University Hospital Münster, Münster, Germany

Department of Otolaryngology, Head and Neck Surgery, University Medicine Greifswald, Münster, Germany e-mail: achimgeorg.beule@ukmuenster.de

G. Gogniashvili Khujadze-Gogniashvili ENT Clinic, Tbilisi, Georgia

G. H. Mlynski Stolpe auf Usedom, Germany e-mail: stolpe@mlynski.com

head of the inferior turbinate and the septal erectile tissue in the anterior cavum, the airstream is directed to the turbinate region and distributed over its entire cross-sectional surface. The degree of turbulence is regulated.

• In the functional area, the nasal turbinates not only represent a large surface, but through their adaptation in shape and size, they also narrow the nasal cave to an uniform slitshaped space between the septum and the lateral wall of the cavum, which promotes warming up, humidication, and cleansing of the inspired air.

• The inspiratory outow area consists of the nasopharyngeal meatus, the choanae, and the nasopharynx. Here the airow becomes increasingly laminar and is redirected to the deeper air passages.

• A large thermal energy and humidity gradient are required between the mucosa and the airstream for effective warming and humidication of the air in the nose. The nasal cycle assures these conditions.

• The division of the nose into two sides by the septum makes it possible to alternate between working and resting phases to improve gradients of thermal energy and humidity exchange over a long time period.

• The nasal septum is rarely completely straight within the generally asymmetrical human skull. By means of a “physiological deviation” of the septum and adaptation of the con-

https://doi.org/10.1007/978-3-031-12386-3_20

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guration of the turbinates, a symmetrical slit-shaped space results on each side of the nose. Cyclical congestion and decongestion of the turbinates make it possible to have in both nasal sides adequate working and resting phases.

• A more intense involvement of physiological aspects in functional rhinology is essential to improve long-term results of functional rhinosurgery.

20.1 Preliminary Remarks

For an undisturbed gas exchange in the lung, a temperature of 37°C and a relative humidity of 100% are essential. The respiratory function of the nose is to climatize up to 25.000L of inspired air every day [1]. For that, an important requirement is a physiologic resistance of nasal breathing, because increased nasal obstruction will result in habitual partially or completely mouthbypass breathing. From physiology, the appropriate relation of physical activity and required airow achieving a sufcient oxygen supply during inspiration is known (Fig. 20.1). During physiological activities, like walking or climbing stairs, a maximal inspiration ow up to 500mL/s

is needed. This range of airow is called “physiological breathing range”. During strong physical work airow will increase up to >1.000L, within the “stress breathing range” (Fig.20.1).

To exert the respiratory function of the nose, the necessary breathing volumes should be achieved without any mouth-bypass breathing. Both nasal sides attributed to this respiratory capacity during the nasal cycle using a constantly changing degree of congestion. The degree of congestion is constantly changed also in relation to physical activity (see Sect. 20.5). Within the physiological breathing range, resistance on both sides of the nose (see Sect. 20.2.1), the sections of turbulent ow (see Sect. 20.4), and the inspiratory nasal valve collapse (see Sect. 20.2.2) should behave physiological.

During increasing physical activity, maximal inspiratory velocities up to 1000 mL/s become mandatory. Because endonasal resistance increases exponentially with increasing nasal ow (see Sect.

20.2.1) and physiological nasal valve function

impedes high airow (see Sect. 20.2.2), endonasal air velocities of 1000 mL/s cannot be provided through the nose alone. As a consequence, in the stress breathing range during heavy and very heavy physical activity respiration switched subsequently to mouth breathing (Fig.20.1).

Fig. 20.1 Schematic representation of the relationship between physical activity and maximal inspiratory airow velocity (Flow [mL/s]). Classication into a “physiological breathing range” during normal physical activity and “stress breathing range” during strong physical activity, including their relationship to nasal and mouth breathing

Physical

activity

Very heavy

Very fast

climb stairs

Heavy

Fast

climb stairs

Moderate

climb stairs

Slight

walk

rest

Maximum

inspir. flow

>1000 ml/s

750 ml/s

500 ml/s

250 ml/s

125 ml/s

Breathing

range

Stress

breathing

range

Physiological

breathing

range

mouth-nose breathing

Ratio

Mouth

breathing

Mouth-bypass-

breathing

Nose

breathing

CrossSectional Area

ResistanceWallArea~

ResistanceTurbulentFlowPortions

–750 –500 –250 250 500 750

R[sPa/ml] R[sPa/ml]

Flow[ml/s] –750 –500 –250 250 500 750Flow[ml/s]

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20.2 Nasal Airway Resistance

The ow resistance is a consequence of the friction- related energy loss. With laminar ow, the particles owing forward rub against each other due to their different ow velocities. Friction and thus the resistance decrease as the cross-sectional area of the ow channel increases, because the distance between the owing particles increases. The cross-sectional area of a channel is therefore indirectly related to its ow resistance:

Resistance

Friction also arises at the wall of the airow channel. Therefore, endonasal resistance is also determined in relation to the size of the endonasal surface (mucosal coverage of the airow channel). The larger the endonasal surface, the larger the nasal resistance:

Turbulent ow sections also have an inuence on the resistance. In turbulence, lateral movements cause the owing air particles to bump against one another and against the wall of the channel. This leads to a high loss of energy and thus to an increase in resistance:

−

Within the nose, nasal resistance increases exponentially with increasing ow due to the increasing sections of turbulent airow. Figure20.2 indicates the development of resistance in relation to nasal airow during in- and expiration in a patient with pathologic high resistance at nasal obstruction on the right side and physiological low nasal resistance on the left side.

20.2.1 Physiological

andPathological Nasal Airow Resistance

A physiologically low resistance in the nasal

ow channel enables an unhindered airow.

For the deeper airways, it has the function of

an upstream resistor to protect the mucosa

against excessive ow. In patients with pathologically low nasal resis-

tance, this effect as protective upstream resis-

tor is insufcient. A physiologically increased nasal resistance is

observed due to congestion during the resting

phase of the nasal cycle (see Sect. 20.5). Nasal

obstruction is only perceived, if the contralat-

3.0

2.5

2.0

1.5

1.0

0.5

Inspiration

0.0

Fig. 20.2 Exponential increase of nasal resistance with increasing ow due to increasing turbulent ow portions during in- and expiration. Red line indicates the right side: pathological increased resistance due to lots of turbulent

Expiration Inspiration Expiration

3.0

2.5

2.0

1.5

1.0

0.5

0.0

portions with complaints of nasal obstruction. Blue line indicates the left side: physiological low nasal resistance due to low portions of turbulence without subjective nasal obstruction

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Resistance

Cross-sectional area

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Fluid dynamic causes of nasal obstruction

Narrowing

by mucosal

swelling

Fig. 20.3 Flow dynamic aetiologies of nasal obstruction

by skeletal

deformity

by pathological

valve collapse

eral side in its working phase does not allow a sufcient airow for oxygen supply within the physiological breathing range.

Pathologically increased nasal resistance may

uni- or bilaterally cause the symptom of nasal obstruction due to several ow dynamic aetiologies (Fig.20.3):

• Stenosis due to – Swelling due to inammation, trauma,

or tumour.

– Skeletal constricting deformations, such

as septal deviation, isthmus stenosis, or other.

– Pathological nasal inspiratory collapse

(see Sect. 20.2.2).

• Pathological turbulence (see Sect. 20.5).

In narrowings, the friction is increased because the owing particles become more compressed. The relationship of resistance and cross-sectional area is not linear, but exponential (Fig.20.4). As a result, in a wide ow channel, a large reduction in cross-sectional area only leads to a slight increase of resistance, but in case of an already narrow cross-sectional area, even a small reduction in size causes a large increase of resistance.

20.2.2 Short-Time Regulation

ofNasal Airway Resistance

The short-time regulation of the nasal respiratory ow by changing the resistance is the suction (Bernoulli phenomenon) of the nasal valve in the

Pathological

turbulence

by small diffuser

inflow opening

Internal

ostium

Fig. 20.4 Different effects of narrowing of the crosssectional area within the nasal airow channel on nasal resistance in the internal ostium (blue area) and the middle of the nasal cavum (red area)

by large diffuser

opening angle

Middle of the cavum

nasal entrance rst described by Mink [2] with the effect of increasing resistance. There are two physiological narrowings with a movable lateral wall: the internal ostium (“Isthmus “or “inner nasal valve”) and the external ostium (“outer nasal valve”). The local ow velocity increases in the constrictions of a ow channel. According to the Bernoulli phenomenon, this results in negative pressure on the wall of the ow channel (principle of the water jet pump). When the ow rate is high, the mobile lateral nasal wall is sucked in and moves medially, thus considerably increasing the resistance in a fraction of a second. This mechanism is only possible during inspiration, because during expiration the pressure in the vestibulum is positive.

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This physiological nasal valve collapse is a protective passive mechanism for the respiratory mucosa of the nose and the subsequent airways, preventing pathologically increased airow velocities and possible damage due to shear forces.

In contrast, pathological nasal valve collapse is observed if medial movement of the lateral nasal wall already occurs at lower nasal airow velocities. This can be caused not only by an additional pathological narrowing of the already physiologically narrow ow channel but also by a loss of stability of the lateral vestibular wall.

20.2.3 Long-Term Regulation

oftheNasal Resistance

For long-term regulation of the nasal resistance, cross-sectional diameter of the nasal airow channel is modulated via change of endonasal mucosal congestion. Changes take minutes and may persist for hours during inand expiration. It is controlled by the vegetative nervous system and is the basis for the physiological regulation of resistance in the nasal cycle (see Sect. 20.5).

20.3 Nasal Functional Architecture: TheCorrelation oftheStructure andRespiratory Function

From a functional and uid dynamic perspective, the nose is a very complicated structure. Researchers have been attempting to investigate the nasal ow channel for more than 100years [2–20].

For understanding the respiratory function of the nose in connection with the aerodynamics, it is helpful to divide the nose into different areas and to compare anatomical structures of the nose with form elements, whose impact on ow is known from uid physics (Fig. 20.5 and Table20.1).

The schema presented in Fig.20.5 is derived from Bachmann [12, 13] and was then rened after we conducted extensive ow experimental studies [20–22].

The functional area with the turbinates is the principal location for the respiratory function. Here, the air is warmed up, moistened, and cleansed [23, 24]. In inspiratory direction, the inow area is made up of the nasal vestibulum, the nasal isthmus (“internal valve”), and the ante-

Aerodynamic area:

Anatomical nomenclature:

Vestibulum

Aerodynamic form element:

Fig. 20.5 Schematic presentation of dividing the nose into aerodynamic areas and comparative aerodynamic form elements in the inspiratory ow direction

Bend and nozzle

Inflow area

Isthmus

Concave opening

Functional area

Region of turbinates

Anterior cavum

Diffuser Slit space Nozzle

Nasopharyngeal meatus

Outflow area

Chona

Convex

opening

Nasopharynx

Bend an nozzle

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Table 20.1 Fluid dynamic effects of aerodynamic form elements that may be compared to anatomical structures in the nose

Aerodynamic form element Effect on airow

Bend Changing of ow direction Concave opening Divergence of ow paths Convex opening Convergence of ow paths Nozzle Decreasing turbulence, accelerating

ow velocity

Diffuser Increasing turbulence, decelerating

ow velocity

Slit-shaped space Facilitates exchange of heat,

humidity, and cleansing between the mucosa and the respiratory airow

rior cavum with the head of the inferior turbinate and the erectile tissue of the septum. The nasopharyngeal meatus, the choanae, and the epipharynx constitute to the outow area.

20.3.1 Inow Area

The function of the inow area is to congure the airstream in a way to facilitate sufcient contact with the mucosa in the functional area. Figure20.6 illustrates the course and character of ow in the inspiratory airow direction in the inow area of a nasal model [20].

20.3.1.1 Nasal Vestibulum

The nasal vestibulum is shaped like a short, bent tube, and thereby, it acts equivalent to a bend. The curvature is caused by the relative position of the external and internal openings: The ostium externum (inow opening of the bend) is approximately horizontal, and the ostium internum (outow opening of the bend) is more vertically located. The uid dynamic effect of this bend redirects the inspiratory airow from anterior and inferior towards the area of turbinates (Fig.20.6).

In this process, the relative position of the vestibulum to the cavum is of signicance. In a drooping nose with a small nasolabial angle, the vestibulum is rotated with the alar cartilages pointing downwards. During inspiration, this leads to a

A. G. Beule et al.

Fig. 20.6 Flow experimental representation of inspiratory ow in the inow area. White dotted arrows: local ow direction. Laminar ow: only forward movements, turbulent ow: increasing sideways movements. The ow is directed towards the turbinate region (bend effect) and is preserved laminar (nozzle effect). Laminar ow can be recognized from the sharp demarcation between the owing medium and the coloured particles added for visualization. With increasing turbulence, a diffuse colouration develops as a result of lateral movements of the owing particles

very high ow course within the cavum (Fig.20.7b). As a result, the mucosa of the inferior turbinate cannot contribute to the respiratory function. If the nasolabial angle is too large, the vestibulum and the alar cartilage are rotated upwards. As a consequence, the airstream runs very low through the cavum, and thus, the mucosa of the upper turbinate is not capable of contributing to respiratory and olfaction function (Fig.20.7c).

When the vestibulum is malpositioned, the entire nasal ow channel is not employed for the respiratory function of the nose. This results in a functional airstream constriction, similar to an anatomical constriction. It results in an increased airway resistance as well. Therefore, correction of an inadequate or excessive nasolabial angle is necessary not only for aesthetic reasons but also from a functional point of view.

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