Impaired Air Conditioning within the Nasal Cavity in Flat-Faced Homo

Beyond skeletal studies: A computational analysis of nasal airway function in climate adaptation

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.

Nasal anatomy and sniffing in respiration and olfaction of wild and domestic animals

Animals have been widely utilized as surrogate models for humans in exposure testing, infectious disease experiments, and immunology studies. However, respiratory diseases affect both humans and animals. These disorders can spontaneously affect wild and domestic animals, impacting their quality and quantity of life. The origin of such responses can primarily be traced back to the pathogens deposited in the respiratory tract. There is a lack of understanding of the transport and deposition of respirable particulate matter (bio-aerosols or viruses) in either wild or domestic animals. Moreover, local dosimetry is more relevant than the total or regionally averaged doses in assessing exposure risks or therapeutic outcomes. An accurate prediction of the total and local dosimetry is the crucial first step to quantifying the dose-response relationship, which in turn necessitates detailed knowledge of animals' respiratory tract and flow/aerosol dynamics within it. In this review, we examined the nasal anatomy and physiology (i.e., structure-function relationship) of different animals, including the dog, rat, rabbit, deer, rhombus monkey, cat, and other domestic and wild animals. Special attention was paid to the similarities and differences in the vestibular, respiratory, and olfactory regions among different species. The ventilation airflow and behaviors of inhaled aerosols were described as pertinent to the animals' mechanisms for ventilation modulation and olfaction enhancement. In particular, sniffing, a breathing maneuver that animals often practice enhancing olfaction, was examined in detail in different animals. Animal models used in COVID-19 research were discussed. The advances and challenges of using numerical modeling in place of animal studies were discussed. The application of this technique in animals is relevant for bidirectional improvements in animal and human health.

Exploring the influence of nasal vestibule structure on nasal obstruction using CFD and Machine Learning method

Motivated by clinical findings about the nasal vestibule, this study analyzes the aerodynamic characteristics of the nasal vestibule and attempt to determine anatomical features which have a large influence on airflow through a combination of Computational Fluid Dynamics (CFD) and machine learning method. Firstly, the aerodynamic characteristics of the nasal vestibule are detailedly analyzed using the CFD method. Based on CFD simulation results, we divide the nasal vestibule into two types with distinctly different airflow patterns, which is consistent with clinical findings. Secondly, we explore the relationship between anatomical features and aerodynamic characteristics by developing a novel machine learning model which could predict airflow patterns based on several anatomical features. Feature mining is performed to determine the anatomical feature which has the greatest impact on respiratory function. The method is developed and validated on 41 unilateral nasal vestibules from 26 patients with nasal obstruction. The correctness of the CFD analysis and the developed model is verified by comparing them with clinical findings.

In-silico decongested trial effects on the impaired breathing function of a bulldog suffering from severe brachycephalic obstructive airway syndrome

BACKGROUND AND OBJECTIVE

Brachycephalic obstructive airway syndrome (BOAS) susceptible dogs (e.g., French bulldog), suffer health complications related to deficient breathing primarily due to anatomical airway geometry. Surgical interventions are known to provide acceptable functional and cosmetic results; however, the long-term post-surgery outcome is not well known. In silico analysis provides an objective measure to quantify the respiratory function in postoperative dogs which is critical for successful long-term outcomes. A virtual surgery to open the airway can explore the ability for improved breathing in an obstructed airway of a patient dog, thus supporting surgeons in pre-surgery planning using computational fluid dynamics.

METHODS

In this study five surgical interventions were generated with a gradual increment of decongested levels in a bulldog based on computed tomography images. The effects of the decongested airways on the breathing function of a patient bulldog, i.e., airflow characteristics, pressure drop, wall shear stress, and air-conditioning capacity, were quantified by benchmarking against a clinically healthy bulldog using computational fluid dynamics (CFD) method.

RESULTS

Our findings demonstrated a promising decrease in excessive airstream velocity, pressure drop, and wall shear stress in virtual surgical scenarios, while constantly preserving adequate air-conditioning efficiency. A linear fit curve was proposed to correlate the reduction in the pressure drop and decongested level.

CONCLUSIONS

The in silico analysis is a viable tool providing visual and quantitative insight into new unexplored surgical techniques.

Relationships between the hard and soft dimensions of the nose in Pan troglodytes and Homo sapiens reveal the positions of the nasal tips of Plio-Pleistocene hominids

By identifying homogeneity in bone and soft tissue covariation patterns in living hominids, it is possible to produce facial approximation methods with interspecies compatibility. These methods may be useful for producing facial approximations of fossil hominids that are more realistic than currently possible. In this study, we conducted an interspecific comparison of the nasomaxillary region in chimpanzees and modern humans with the aim of producing a method for predicting the positions of the nasal tips of Plio-Pleistocene hominids. We addressed this aim by first collecting and performing regression analyses of linear and angular measurements of nasal cavity length and inclination in modern humans (Homo sapiens; n = 72) and chimpanzees (Pan troglodytes; n = 19), and then performing a set of out-of-group tests. The first test was performed on four subjects that belonged to the same genus as the training sample, i.e., Homo (n = 2) and Pan (n = 2), and the second test, which functioned as an interspecies compatibility test, was performed on Pan paniscus (n = 1), Gorilla gorilla (n = 3), Pongo pygmaeus (n = 1), Pongo abelli (n = 1), Symphalangus syndactylus (n = 3), and Papio hamadryas (n = 3). We identified statistically significant correlations in both humans and chimpanzees with slopes that displayed homogeneity of covariation. Prediction formulae combining these data were found to be compatible with humans and chimpanzees as well as all other African great apes, i.e., bonobos and gorillas. The main conclusion that can be drawn from this study is that our set of regression models for approximating the position of the nasal tip are homogenous among humans and African apes, and can thus be reasonably extended to ancestors leading to these clades.

Three-dimensional form and function of the nasal cavity and nasopharynx in humans and chimpanzees

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.

N95 respirator mask breathing leads to excessive carbon dioxide inhalation and reduced heat transfer in a human nasal cavity

Face masks and respirators are used to filter inhaled air, which may contain airborne droplets and high particulate matter (PM) concentrations. The respirators act as a barrier to the inhaled and exhaled air, which may change the nasal airflow characteristics and air-conditioning function of the nose. This study aims to investigate the nasal airflow dynamics during respiration with and without an N95 respirator driven by airflow through the nasal cavity to assess the effect of the respirator on breathing conditions during respiration. To achieve the objective of this study, transient computational fluid dynamics simulations have been utilized. The nasal geometry was reconstructed from high-resolution Computed Tomography scans of a healthy 25-year-old female subject. The species transport method was used to analyze the airflow, temperature, carbon dioxide (CO₂), moisture content (H₂O), and temperature distribution within the nasal cavity with and without an N95 respirator during eight consecutive respiration cycles with a tidal volume of 500 ml. The results demonstrated that a respirator caused excessive CO₂ inhalation by approximately 7 × greater per breath compared with normal breathing. Furthermore, heat and mass transfer in the nasal cavity was reduced, which influences the perception of nasal patency. It is suggested that wearers of high-efficiency masks that have minimal porosity and low air exchange for CO₂ regulation should consider the amount of time they wear the mask.

Common evolutionary patterns in the human nasal region across a worldwide sample

OBJECTIVES

Variation in the external nasal region among human populations has long been proposed in the literature to reflect adaptations to facilitate thermoregulation, air conditioning, and moisture retention in local climates and environments. More specifically, adaptations in populations living in colder climates have often been assumed due to correlational relationships found between variation in the nasal region and climatic variables. Here, we test this hypothesis by applying a quantitative genetics approach based on the Lande model to assess whether variation in the nasal region can be explained by random neutral processes (e.g., genetic drift) or if non-random forces (i.e., adaptation) have contributed significantly to its diversity.

MATERIALS AND METHODS

A mixed-sex sample representing 28 population groups from Howells' craniometric dataset were analyzed (n = 2504). Twenty standard measurements were chosen to reflect the external skeletal morphology of the nasal region. We apply statistical tests developed from evolutionary quantitative genetics theory to analyze patterns of within- and between-population divergence under a null hypothesis of genetic drift.

RESULTS

This study finds a rejection of genetic drift in all analyses, across tests that involve all 28 populations, exclusively cold-climate populations, and with cold-climate populations excluded, indicating that non-random evolutionary forces have contributed significantly to variation in the nasal region overall.

DISCUSSION

These results show that nasal region adaptation is not exclusive to cold-climate populations, which have often been implicated in the literature to drive nasal variation, instead suggesting that the propensity for adaptation in the nasal region is shared among all human populations.

Computational fluid dynamics comparison of impaired breathing function in French bulldogs with nostril stenosis and an examination of the efficacy of rhinoplasty

BACKGROUND

Brachycephalic obstructive airway syndrome (BOAS) in dogs indicates a particular set of upper airway abnormalities found in brachycephalic dogs (e.g., French bulldogs). Stenotic nares is one of the primary BOAS-related abnormalities restricting the functional breathing of affected dogs. For severe stenosis, rhinoplasty is required to increase the accessibility of the external nostril to air; however, the specific improvement from surgery in terms of respiratory physiology and uptake of inhaled air has not been fully elucidated METHOD: This study employed Computational Fluid Dynamics (CFD) simulations to evaluate the effects of different stenotic intensities on airflow patterns in a total of eight French bulldog upper airways. A bulldog with severe stenosis after surgery was included to examine the efficacy of the surgical intervention.

RESULTS

The results showed homogeneous airflow distributions in healthy and mild stenosis cases and significantly accelerated airstreams at the constricted positions in moderate and severe stenosis bulldogs. The airflow resistance was over 20-fold greater in severe stenosis cases than the healthy cases. After surgery, a decrease in airflow velocity was observed in the surgical region, and the percentage of reduced airflow resistance was approximately 4%.

CONCLUSIONS

This study suggests impaired breathing function in brachycephalic dogs with moderate and severe stenosis. The results also serve as a reference for veterinarians in surgical planning and monitoring bulldogs' recuperation after surgery.

Computational fluid dynamics simulation wall model predicting air temperature of the nasal passage for nonhuman primates

OBJECTIVES

Nasal passages adjust the temperature of inhaled air to reach the required body temperature for the lungs. The nasal regions of primates including humans are believed to have experienced anatomical modifications that are adaptive to effective conditioning of the atmospheric air in the habitat for a given species. Measurements of the nasal temperature are required to understand the air-conditioning performance for a given species. Unfortunately, repeated direct measurements within the nasal passage have been technically precluded in most nonhuman primates.

MATERIALS AND METHODS

Computational fluid dynamics (CFD) simulation is a potential approach for examining the temperature profile in the nasal passage without any direct measurements. The CFD simulation model mainly comprises a computational model to simulate physiological mechanisms and a wall model to simulate the nasal passage's anatomical and physical properties. We used a computational model developed for humans and examined corrections for the developed wall model based on human properties for predicting its performance in Japanese macaques.

RESULTS

This study confirmed that the epithelium layer thickness of the wall model affects the accuracy of the predictions for macaques. A convenient correction of the thickness based on body mass allows us to simulate the actual air temperature profile in macaques' nasal passage.

DISCUSSION

The CFD simulations of the wall model corrected with body mass can be applied to other nonhuman primates and mammals. This convenient corrective approach allows us to examine the functional contributions of a specific morphology to the air-conditioning performance without any direct measurements to improve our understanding of primates' functional morphology and physical adaptations to the temperature environment in their habitat.

Voxel-based simulation of flow and temperature in the human nasal cavity

The nasal airway is an extremely complex structure, therefore grid generation for numerical prediction of airflow in the nasal cavity is time-consuming. This paper describes the development of a voxel-based model with a Cartesian structured grid, which is characterized by robust and automatic grid generation, and the simulation of the airflow and air-conditioning in an individual human nasal airway. Computed tomography images of a healthy adult nose were used to reconstruct a virtual three-dimensional model of the nasal airway. Simulations of quiet restful inspiratory flow were then performed using a Neumann boundary condition for the energy equation to adequately resolve the flow and heat transfer. General agreements of airflow patterns, which were a high-speed jet posterior to the nasal valve and recirculating flow that occupied the anterior part of the upper cavity, and temperature distributions of the airflow and septum wall were confirmed by comparing in-vivo measurements with numerical simulation results.

Details of the physiology of the aerodynamic and heat and moisture transfer in the normal nasal cavity

Anatomically accurate 3D models of 10 healthy nasal cavities are developed from computerized tomography (CT) scan images. Considering anatomical and physiological importance of different parts of the nasal cavity, the surface of each nasal passage is divided to eleven anatomical surfaces. Also the coronal cross sections in the nasal passage are divided to six sub-sections that share the total nasal passage airflow. The details of the flow field, heat transfer and water-vapor transport are numerically investigated for resting and low activity conditions. The mean and standard deviation of the different anatomical and air conditioning parameters such as: surface area, wall shear stress, heat and moisture transfer on different parts of the nasal passage surfaces and volume flow rates through different sections are presented. Results show that the percentages of airflow for inferior, middle and superior meatuses are 11.3 ± 6.4, 36.5 ± 9.5, 1.9 ± 0.81 % respectively and 4.1 ± 2.1 % of air passes through olfactory area. The inhaled air passing from the remaining surface (main passage) is 46.2 ± 10 %. Heat and moisture fluxes are highest in the anterior part of the nasal cavity, turbinates and lower part of the septum respectively. The percentage of the heat transfer from turbinates is 25.7 ± 3.9 % of total nasal heat transfer.

THE EXPOSOME IN HUMAN EVOLUTION: FROM DUST TO DIESEL

Global exposures to air pollution and cigarette smoke are novel in human evolutionary history and are associated with about 16 million premature deaths per year. We investigate the history of the human exposome for relationships between novel environmental toxins and genetic changes during human evolution in six phases. Phase I: With increased walking on savannas, early human ancestors inhaled crustal dust, fecal aerosols, and spores; carrion scavenging introduced new infectious pathogens. Phase II: Domestic fire exposed early Homo to novel toxins from smoke and cooking. Phases III and IV: Neolithic to preindustrial Homo sapiens incurred infectious pathogens from domestic animals and dense communities with limited sanitation. Phase V: Industrialization introduced novel toxins from fossil fuels, industrial chemicals, and tobacco at the same time infectious pathogens were diminishing. Thereby, pathogen-driven causes of mortality were replaced by chronic diseases driven by sterile inflammogens, exogenous and endogenous. Phase VI: Considers future health during global warming with increased air pollution and infections. We hypothesize that adaptation to some ancient toxins persists in genetic variations associated with inflammation and longevity.

CFD analysis of the flow structure in a monkey upper airway validated by PIV experiments

Inhalation exposure to airborne contaminants has adverse effects on humans; however, related research is typically conducted using in vivo/in vitro tests on animals. Extrapolating the test results is complicated by anatomical and physiological differences between animals and humans and a lack of understanding of the transport mechanism inside their respective respiratory tracts. This study determined the detailed air-flow structure in the upper airway of a monkey. A steady computational fluid dynamics simulation, which was validated by previous particle image velocimetry measurements, was adopted for flow rates of 4 L/min and 10 L/min to analyze the flow structure from the nasal/oral cavities to the trachea region in a monkey airway model. The low Reynolds number type k-ε model provided a reasonably accurate prediction of the airflow in a monkey upper airway. Furthermore, it was confirmed that large velocity gradients were generated in the nasal vestibule and larynx regions, as well as increased turbulent air kinetic energy and wall sheer stress.

Temperature profile of the nasal cavity in Japanese macaques

The nasal cavity conditions respiratory air. The distribution of temperature within the nasal cavity has been examined in humans using various direct measurements. Macaques are a nonhuman primate species that are used as a model for understanding human physiology. They are widely distributed geographically in varied climate environments and they are expected to exhibit evolutionary anatomical and physiological adaptations in the air-conditioning. To provide basic data for developing an animal model in air-conditioning, we measured the distribution of temperature within the nasal cavity in Japanese macaques, Macaca fuscata. Inhaled air was well conditioned in the vestibular cavity and was almost fully conditioned before reaching the nasopharynx. This conditioning performance is better than that in humans. The anatomical and histological features of the nasal cavity are expected to explain this difference in physiological performance between the two species. These data will be helpful in establishing an animal model to understand and model airway air-conditioning performance in macaques and humans.

The navigational nose: a new hypothesis for the function of the human external pyramid

One of the outstanding questions in evolution is why Homo erectus became the first primate species to evolve the external pyramid, i.e. an external nose. The accepted hypothesis for this trait has been its role in respiration, to warm and humidify air as it is inspired. However, new studies testing the key assumptions of the conditioning hypothesis, such as the importance of turbulence to enhance heat and moisture exchange, have called this hypothesis into question. The human nose has two functions, however, respiration and olfaction. It is thus also possible that the external nose evolved in response to selection for olfaction. The genus Homo had many adaptations for long-distance locomotion, which allowed Homo erectus to greatly expand its species range, from Africa to Asia. Long-distance navigation in birds and other species is often accomplished by orientation to environmental odors. Such olfactory navigation, in turn, is enhanced by stereo olfaction, made possible by the separation of the olfactory sensors. By these principles, the human external nose could have evolved to separate olfactory inputs to enhance stereo olfaction. This could also explain why nose shape later became so variable: as humans became more sedentary in the Neolithic, a decreasing need for long-distance movements could have been replaced by selection for other olfactory functions, such as detecting disease, that would have been critical to survival in newly dense human settlements.

Air conditioning analysis among human nasal passages with anterior anatomical variations

A major functional role of the nasal cavity is air conditioning of the inspired environmental air to near alveolar conditions. It is well known that the anatomical disparities among nasal passages can change airflow patterns to a great extent. However, its effect on nasal air conditioning performance remains largely unexplored. This research investigated the nasal air conditioning performance among nasal models with distinct vestibule phenotypes, including subjects with and without vestibule notches. For the mass transfer, we used a two-film theory model to determine the species transport. Airflow patterns, heat and mass transfer between the inhaled airflow and the nasal mucosa were analysed and compared. Results showed that the nasal air conditioning performance is closely related to nasal passage structures. The anatomical variations, especially the geometry changes in the anterior vestibule region, can increase both heat and mass transfer rate between nasal mucous and respiratory air at the vicinity of the notched regions, while for other regions such as the anterior superior nasal cavity, the heat transfer is greatly reduced to even zero heat flux due to lack of active airflow passing.

Computer simulations show that Neanderthal facial morphology represents adaptation to cold and high energy demands, but not heavy biting

Three adaptive hypotheses have been forwarded to explain the distinctive Neanderthal face: (i) an improved ability to accommodate high anterior bite forces, (ii) more effective conditioning of cold and/or dry air and, (iii) adaptation to facilitate greater ventilatory demands. We test these hypotheses using three-dimensional models of Neanderthals, modern humans, and a close outgroup (Homo heidelbergensis), applying finite-element analysis (FEA) and computational fluid dynamics (CFD). This is the most comprehensive application of either approach applied to date and the first to include both. FEA reveals few differences between H. heidelbergensis, modern humans, and Neanderthals in their capacities to sustain high anterior tooth loadings. CFD shows that the nasal cavities of Neanderthals and especially modern humans condition air more efficiently than does that of H. heidelbergensis, suggesting that both evolved to better withstand cold and/or dry climates than less derived Homo We further find that Neanderthals could move considerably more air through the nasal pathway than could H. heidelbergensis or modern humans, consistent with the propositions that, relative to our outgroup Homo, Neanderthal facial morphology evolved to reflect improved capacities to better condition cold, dry air, and, to move greater air volumes in response to higher energetic requirements.

Physical and geometric constraints shape the labyrinth-like nasal cavity

The nasal cavity is a vital component of the respiratory system that heats and humidifies inhaled air in all vertebrates. Despite this common function, the shapes of nasal cavities vary widely across animals. To understand this variability, we here connect nasal geometry to its function by theoretically studying the airflow and the associated scalar exchange that describes heating and humidification. We find that optimal geometries, which have minimal resistance for a given exchange efficiency, have a constant gap width between their side walls, while their overall shape can adhere to the geometric constraints imposed by the head. Our theory explains the geometric variations of natural nasal cavities quantitatively, and we hypothesize that the trade-off between high exchange efficiency and low resistance to airflow is the main driving force shaping the nasal cavity. Our model further explains why humans, whose nasal cavities evolved to be smaller than expected for their size, become obligate oral breathers in aerobically challenging situations.

Nasal airflow simulations suggest convergent adaptation in Neanderthals and modern humans

Both modern humans (MHs) and Neanderthals successfully settled across western Eurasian cold-climate landscapes. Among the many adaptations considered as essential to survival in such landscapes, changes in the nasal morphology and/or function aimed to humidify and warm the air before it reaches the lungs are of key importance. Unfortunately, the lack of soft-tissue evidence in the fossil record turns difficult any comparative study of respiratory performance. Here, we reconstruct the internal nasal cavity of a Neanderthal plus two representatives of climatically divergent MH populations (southwestern Europeans and northeastern Asians). The reconstruction includes mucosa distribution enabling a realistic simulation of the breathing cycle in different climatic conditions via computational fluid dynamics. Striking across-specimens differences in fluid residence times affecting humidification and warming performance at the anterior tract were found under cold/dry climate simulations. Specifically, the Asian model achieves a rapid air conditioning, followed by the Neanderthals, whereas the European model attains a proper conditioning only around the medium-posterior tract. In addition, quantitative-genetic evolutionary analyses of nasal morphology provided signals of stabilizing selection for MH populations, with the removal of Arctic populations turning covariation patterns compatible with evolution by genetic drift. Both results indicate that, departing from important craniofacial differences existing among Neanderthals and MHs, an advantageous species-specific respiratory performance in cold climates may have occurred in both species. Fluid dynamics and evolutionary biology independently provided evidence of nasal evolution, suggesting that adaptive explanations regarding complex functional phenotypes require interdisciplinary approaches aimed to quantify both performance and evolutionary signals on covariation patterns.