The Nasal Valve Dilemma: Title and subTitle BreakThe Narrow Straw vs the Weak Wall

In its simplest anatomical definition, the nasal cavity may be viewed as a longitudinal set of cross-sectional area segments that act as resistors in series, with the overall resistance being dominated by a single flow-limiting region with the least cross-sectional area, ie, the narrowest segment of the “straw.” A great deal of attention has been placed on identification of this resistive segment. This is the region of the nasal valve—internal, external, and the area in between.

As air enters this constricted segment of the airway, acceleration of the airflow occurs. This results in a drop in intraluminal pressure by the Bernoulli principle. The pressure drop can lead to collapse of this segment of the airway during inspiration. Even minor structural deviations of the septum, inferior turbinate, or lateral nasal wall can constrict the nasal valve region and have a great effect on nasal airflow. In addition the intrinsic tensile strength of the “straw walls” affect the ability to withstand the pressure drop that drives the airflow. Given that the septum and turbinate are usually the more rigid structures, it is usually the lateral nasal wall that is the determinant of the nasal valve rigidity.

Surgical correction of 1 or all 3 anatomic deviations (septum, turbinate, and lateral nasal wall) can lead to symptomatic improvement in nasal obstruction. However, it can be difficult to differentiate which of the 3 elements is the most responsible component for the nasal airway obstruction symptoms for any given patient.¹ The surgical philosophies usually fall into the following broad categories:

Available diagnostic tools are limited in the information that is provided to the surgeons in their preoperative assessment and planning. In the ideal setting, the algorithm would allow for the least complex surgery to progress to the more complex ones, eg, would addressing the septum alone be sufficient to increase the diameter of the straw without the need to lateralize and/or increase the rigidity or lateral wall?

The study by Zoumalan et al² provides a context for these questions. With the application of a simulated pressure drop, the nasal valve resistor was tested for its increased diameter and/or the lateral wall strength. It is a simple yet elegant objective measure of improvement that provides feedback in real time and is easily available during surgery at no additional cost. To some extent, the authors also illustrate an algorithmic use of this tool in deciding not to progress from cephalic turn-in flaps to grafts in 2 patients when lateral wall stability was deemed sufficient.

In addition to presenting these features of the method, this study also raises some interesting questions about airflow and pressure effects. As the authors note, the method uses reversed flow through the nose, inducing collapse in a nonphysiologic way. While this aspect of the method does not invalidate its usefulness, it is interesting to note that the natural passage of expired air dilates the nasal vestibule rather than collapsing it. The authors' assessment that depression induced by suction appeared identical to depression seen on strong inspiration was based on external examination. It would be interesting to know if the motion is similar internally as well.

Zoumalan et al² report that the suction used had a minimum pressure of −80 kPa, which is vastly more negative than the pressure that is naturally present in the nose, even during deep breathing. A drawback of the method is an inability to quantify the actual amount of negative pressure applied. In using this method, the surgeon would likely need to develop a feel for the attenuation of this pressure, possibly by adjusting the proximity of the tubing to the nostrils. Because the level of pressure applied is unknown, is it possible that the use of overly negative pressure to judge the sufficiency of repair may lead to overcorrection or overstabilization in some way?

The authors also report that airflow through the suction tubing was set to 50 L/min. This is high for normal nasal airflow, as would be expected from the overly negative pressure in the tubing. While 50 L/min is consistent with physiological airflow rates induced by breathing during exercise, many people switch at such rates from nasal to oronasal breathing, reducing the amount of airflow passing through the nose and thus the nasal resistance. Again, forcing more airflow through the nasal passages than would normally be withstood may be leading to an underestimation of the adequacy of repair.

The study by Zoumalan et al² suggests some interesting avenues to explore further. Control of the pressure applied would provide consistency and allow additional study of the amount and variations of pressure needed in different cases to induce depression. Gradation of surgical effects would also be possible. Internal as well as external examination of applied pressure-induced depression would provide information on the strength of other aspects of vestibular anatomy. This information might provide a way to separate septal and lateral wall contributions to the repair so that maneuvers making the most important changes could be discriminated.

Nevertheless, this study objectively affirms that existing intraoperative surgical techniques for treatment of the nasal valve region improve the ability to overcome a negative pressure drop. Whether that is due to increasing the diameter of the straw or increasing the rigidity of the wall or both is unclear. Also, as noted by the authors, an additional limitation of the study is the lack of patient symptomatology correlation with the final postoperative outcome. However, this study highlights that even the simplest of tools are powerful in providing objective evidence that surgical techniques are effective in addressing the constricted nasal airflow problem. The challenge moving forward is to further refine the evidence to match the intricacies of this surgical problem.