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This study aimed to explore the variability in nasal airflow patterns among different sexes and populations using computational fluid dynamics (CFD). We focused on evaluating the universality and applicability of dimensionless parameters R (bilateral nasal resistance) and ϕ (nasal flow asymmetry), initially established in a Caucasian Spanish cohort, across a broader spectrum of human populations to assess normal breathing function in healthy airways. In this retrospective study, CT scans from Cambodia (20 males, 20 females), Russia (20 males, 18 females), and Spain (19 males, 19 females) were analyzed. A standardized CFD workflow was implemented to calculate R‐ϕ parameters from these scans. Statistical analyses were conducted to assess and compare these parameters across different sexes and populations, emphasizing their distribution and variances. Our results indicated no significant sex‐based differences in the R parameter across the populations. However, moderate sexual dimorphism in the ϕ parameter was observed in the Cambodian group. Notably, no geographical differences were found in either R or ϕ parameters, suggesting consistent nasal airflow characteristics across the diverse human groups studied. The study also emphasized the importance of using dimensionless variables to effectively analyze the relationships between form and function in nasal airflow. The observed consistency of R‐ϕ parameters across various populations highlights their potential as reliable indicators in both medical practice and further CFD research, particularly in diverse human populations. Our findings suggest the potential applicability of dimensionless CFD parameters in analyzing nasal airflow, highlighting their utility across diverse demographic and geographic contexts. This research advances our understanding of nasal airflow dynamics and underscores the need for additional studies to validate these parameters in broader population cohorts. The approach of employing dimensionless parameters paves the way for future research that eliminates confounding size effects, enabling more accurate comparisons across different populations and sexes. The implications of this study are significant for the advancement of personalized medicine and the development of diagnostic tools that accommodate individual variations in nasal airflow. [ABSTRACT FROM AUTHOR]

Objectives: Ecogeographic variation in human nasal anatomy has historically been analyzed on skeletal morphology and interpreted in the context of climatic adaptations to respiratory air‐conditioning. Only a few studies have analyzed nasal soft tissue morphology, actively involved in air‐conditioning physiology. Materials and Methods: We used in vivo computer tomographic scans of (N = 146) adult individuals from Cambodia, Chile, Russia, and Spain. We conducted (N = 438) airflow simulations during inspiration using computational fluid dynamics to analyze the air‐conditioning capacities of the nasal soft tissue in the inflow, functional, and outflow tract, under three different environmental conditions: cold–dry; hot–dry; and hot–humid. We performed statistical comparisons between populations and sexes. Results: Subjects from hot–humid regions showed significantly lower air‐conditioning capacities than subjects from colder regions in all the three conditions, specifically within the isthmus region in the inflow tract, and the anterior part of the internal functional tract. Posterior to the functional tract, no differences were detected. No differences between sexes were found in any of the tracts and under any of the conditions. Discussion: Our statistical analyses support models of climatic adaptations of anterior nasal soft tissue morphology that fit with, and complement, previous research on dry skulls. However, our results challenge a morpho‐functional model that attributes air‐conditioning capacities exclusively to the functional tract located within the nasal cavity. Instead, our findings support studies that have suggested that both, the external nose and the intra‐facial soft tissue airways contribute to efficiently warming and humidifying air during inspiration. This supports functional interpretations in modern midfacial variation and evolution. [ABSTRACT FROM AUTHOR]

This paper presents an updated view on the morphological and functional significance of the human respiratory system in the context of human evolutionary anatomy. While usually the respiratory system is treated either from a craniofacial perspective, mostly in the context of nasal evolution and air-conditioning, or from a postcranial perspective featuring on overall thoracic shape changes, here we pursue a holistic perspective on the form, function, integration, and evolutionary change of the entire organismal system in hominins. We first present a brief review of the most important morphological structures, their function, and its potential integration and interaction with the nasal cavity and thoracic skeleton. This is followed by an overview of the most important improvements in methods for the comparative study in recent humans and fossil hominins. We then overview and list a compendium of hominin fossil material currently available for the study. We propose four functional categories of hominin respiratory system configurations that differ potentially with respect to size, shape, biomechanics and/or bioenergetics. Finally, we discuss these and speculate on possible ways for future research into an anatomical system that, despite its under-investigated status, is central to the understanding of the form and functions of the hominin organism and its paleobiology.

The facial differences between recent Pan troglodytes and Homo sapiens can be used as a proxy for the reduction of facial prognathism that happened during evolutionary transition between Australopithecines and early Homo. The projecting nasal morphology of Homo has been considered both a passive consequence of anatomical reorganization related to brain and integrated craniofacial evolution as well as an adaptation related to air-conditioning during physiological and behavioral shifts in human evolution. Yet, previous research suggested impaired air-conditioning in Homo challenging respiratory adaptations based on computational fluid dynamics (CFD) and airflow simulations. Here we improved CFD model at the inflow region and also carried out three-dimensional (3D) geometric morphometrics to address the hypothesis of impaired air-conditioning in humans and species differences in airway shape. With the new CFD model we simulated pressure, velocity, and temperature changes in airflow of six adult humans and six chimpanzees and analyzed 164 semi-landmarks of 10 humans and 10 chimpanzees for 3D size and shape comparisons. Our finding shows significantly different internal 3D nasal airways. Also, species means of pressure, velocity, and temperature differed statistically significantly. However, form-related differences in temperature exchanges seem subtle and may question adaptive disadvantages. We rather support a hypothesis of craniofacial changes in the Australopithecus-Homo transition that are related to brain evolution and craniofacial integration with facial and nasal modifications that contribute to maintain respiratory adaptations related to air conditioning., (© 2021 The Authors. The Anatomical Record published by Wiley Periodicals LLC on behalf of American Association for Anatomy.)