Discussion
The present study focused on relationships between nasal morphological variations due to inter- and intra-racial differences and gender, which differs from previously published studies by our group investigating nasal morphological variations.2, 18 Unlike this study that categorizes nasal index by subjects’ race/ethnicity with gender, and gender separately; Patki and Frank-Ito2 explored the relationship between nasal index and CFD simulated airflow-related variables, such as nasal resistance, wall shear stress, and heat flux.
Although Keeler et al.18 modeled deposition patterns of individuals across the same four race/ethnic groups as the present study, as well as briefly reported results of SAV ratio, nasal resistance and nasal index across races/ethnicities; the present student conducted an in-depth analysis of both anatomical and airflow-related variables in the same race/ethnic groups with gender as a factor. Additionally, Keeler et al.18 included the paranasal sinuses in their CFD models while the present study excluded the paranasal sinuses are they have negligible effects on physiological functions pertaining to the main nasal cavities.
Nasal index results are in agreement with reports on climate-related variation in human nose, suggesting that individuals that evolved from colder and drier climates tended to have smaller nasal index than individuals from warmer and more humid climates.2, 12, 18, 19 Results in this study pertaining to nasal index and gender are consistent with those previously reported by Ravichandran et al.20 In their paper, Ravichandran and colleagues found that nasal index is a reliable parameter for the estimation of gender difference, noting that the average value of nasal indices of South Indian males was greater than South Indian females.20 Additionally, in a study examining the nasal index of the Kosovo Albanian population, males had a significantly higher nasal index than females (p < 0.001).21 While similar conclusions can be made with the Caucasian population from the present study, it should be noted that the difference in median nasal index between Caucasian males and females was 0.66. Additionally, when comparing nasal index and gender by race, East Asian and Black females had larger average nasal index than their male counterparts.
The current literature is sparse regarding the relationship between nasal resistance and race/ethnicity. Keeler et al.18reported that average nasal resistance for African Americans and Caucasians were lowest and highest, respectively. Other studies have reported no significant differences in nasal resistance between African descents and Caucasians.19, 22, 23 Babatola measured nasal resistance of African descents from Nigeria and concluded that nasal resistance in this population was similar to those of Caucasians and Asians.22 Calhoun et al. and Ohki et al.19, 23 also arrived at similar conclusions in their studies. Our results suggest that median nasal resistance was highest among Caucasians, followed by Blacks before Latinos, and East Asians had the lowest median nasal resistance values. Nonetheless, it should be noted that the IQR values for Blacks and East Asians were particularly larger than those of Caucasians and Latinos, implying there could be possible overlap among the groups, which may indicate non-significant differences among groups.
Our findings indicate females have a larger nasal resistance than males. This trend was seen within every race except for Caucasians when comparing between nasal resistance and race and gender. A study conducted by Warren et al.24 revealed no significant difference in resistances for males and females with normal nasal anatomy. However, Ren et al.25 reported that mean nasal resistance in males were significantly lower than females among a cohort of healthy subjects in China.
The main limitation from the present study pertains to our relatively small sample size. Although there were 16 subjects, each race had 4 subjects, and after further stratification by race and gender, there were 2 subjects per group. In conclusion, this study investigated the relationships between normal nasal morphological variations due to inter- and intra-racial and gender differences in subject-specific nasal airway models from 16 subjects across 4 racial groups. Findings from the present work indicate that there is an association between normal nasal anatomical variabilities across race and gender. However, these variabilities may not discriminate proper functioning of the nasal cavity across race and gender.