Changes in nasal airflow and heat transfer correlate with symptom improvement after surgery for nasal obstruction
Introduction
Nasal airway obstruction (NAO) is a common affliction (Jessen and Malm, 1997). Surgeries to correct anatomic deformities contributing to NAO are often successful, but many such procedures have less desirable outcomes (Andre et al., 2006, Dinis and Haider, 2002, Illum, 1997, Singh et al., 2006). Studies investigating non-desirable outcomes have noted a lack of clinical tools providing consistent, objective measures of nasal physiology. In addition, difficulties correlating measurements with patient-reported symptoms indicate that new tools and measures are needed (Kjaergaard et al., 2008, Lam et al., 2006, Pawar et al., 2010, Rhee, 2009, Schumacher, 2002).
Computational fluid dynamics (CFD) is a tool that can fill this need. CFD modeling of nasal physiology has evolved from two-dimensional airflow simulations in simplified channels (Tarabichi and Fanous, 1993) to three-dimensional models of airflow, heat, water vapor, and inhaled material transport in anatomically-accurate reconstructions of the nasal passages based on medical images (Chen et al., 2009, Frank et al., 2013, Garcia et al., 2007, Kimbell et al., 2007, Lindemann et al., 2006, Rhee et al., 2012, Subramaniam et al., 1998, Wexler et al., 2005). Nasal CFD models can estimate many physiologically relevant variables in exquisite anatomical detail, and are the focus of an increasing number of studies (Leong et al., 2010, Wang et al., 2012).
For CFD to be useful to nasal surgeons, variables must be identified that reflect surgical changes and correlate with symptoms, e.g., feelings of congestion, blockage, breathing difficulties, sleep disturbance, and air hunger (Rhee and McMullin, 2008). Nasal resistance is affected by reduction in airway cross-sectional area and may relate to congestion and blockage. Abnormal patterns of airflow may disrupt normal sensation stimuli (Garcia et al., 2007) so that airflow and wall shear stress may relate to congestion, breathing difficulties, air hunger, irritation, and pain that disturbs sleep. The nose is a finely-tuned heat regulator and contains densely distributed thermoreceptors in the nasal vestibule (Jones et al., 1989). Disruption of these systems may lead to extreme mucosal drying and/or cooling with compensatory excesses in blood flow and mucus production, or lack of airflow sensation with increased feelings of congestion. Such disruptions can be inferred from CFD simulations.
CFD models have been used to estimate surgical effects on some of these variables but studies are lacking that test the discriminatory capability of these variables with respect to surgery, or relate these variables to patient symptoms. As part of a prospective study designed to fill these gaps, we developed methods to compare CFD-derived nasal resistance (CFD-NR) with validated patient-reported measures of NAO symptoms before and after surgery. In a preliminary application of these methods to two NAO patients, no relationship was evident between bilateral CFD-NR and symptom severity but a positive trend emerged when bilateral CFD-NR was replaced with unilateral CFD-NR on the most obstructed nasal side (Kimbell et al., 2012).
The goals of the present study were to expand these results to a larger cohort of NAO patients and compute airflow, wall shear stress, and heat flux in addition to CFD-NR pre- and post-surgery. The results were used to test the hypotheses that these variables can (1) discriminate between pre-surgery and post-surgery states, and (2) correlate with scores from symptom surveys administered before and after surgery.
Section snippets
Patient reported measures
The patient-reported measures of NAO symptoms used here were the Nasal Obstruction Symptom Evaluation (NOSE) scale to assess general symptomology and quality of life, and a 0-to-10 visual analog scale (VAS) for unilateral airflow sensation. The NOSE scale has been validated for NAO symptoms (Stewart et al., 2004a, Stewart et al., 2004b) and consists of patient ratings, over the past month, of feelings of (1) nasal congestion or stuffiness, (2) nasal blockage or obstruction, (3) trouble
Surveys
NOSE scores (Table 2) improved with surgery in nine subjects and were the same pre- and post-operatively in one subject. On average, post-surgery NOSE scores were lower than pre-surgery scores (Fig. 4A). As expected, since the NOSE instrument has been validated for assessing NAO symptoms (Stewart et al., 2004a), pairwise differences between pre- and post-surgery NOSE scores were statistically significant (Table 3). VAS scores on the most obstructed nasal side (VAS-OS) improved with surgery in
Discussion
In order to improve the success rate of NAO surgery using CFD, biophysical variables need to be identified that can be markers for symptoms of NAO so that these variables can eventually help guide virtual surgeries. Nasal airflow, resistance, heat flux, and wall shear were selected for this report due to the symptom relevance of airway constriction (Garcia et al., 2010), correlation of heat flux with perceived patency ratings (Zhao et al., 2011), and the potential mechanoreceptor stimulator
Conflict of interest statement
To the best of our knowledge, no conflicts of interest exist for any of the authors.
Acknowledgments
The authors thank Nikki Stelse, Sachin Pawar and Daniel Cannon for contributions to this work. This research was funded by Grants R01EB009557 and R01EB009557-01S1 from the National Institutes of Health/National Institute of Biomedical Imaging and Bioengineering to the Medical College of Wisconsin (MCW) and by subcontract from MCW to the University of North Carolina at Chapel Hill. This description of results from this research is solely the responsibility of the authors and does not represent
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