A Mass Transport Model of Olfaction
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Abstract:
A theoretical model of olfaction involving all the major mechanisms in the mass transport of odorant molecules from inspired air to the olfactory receptors is developed. The mechanisms included are: (i) convective bulk flow of odorant molecules to the olfactory region of the nasal cavity by inhaled air, (ii) lateral transport of odorant molecules from the flowing gas stream in the olfactory region onto the olfactory mucus surface, (iii) sorption of odorant molecules into the mucus at the air-mucus interface, (iv) diffusion of odorant molecules through the mucus layer, and (v) interaction of odorant molecules with the olfactory receptor cells. The model is solved to yield the olfactory response as a function of various physical variables such as the inspiratory flow rate, the mass transfer coefficient, the initial concentration of odorant molecules in the inhaled air, the length of the olfactory mucosa, the thickness of the olfactory mucosa, and the air-mucus partitioning (or solubility in the mucus) of odorant molecules. It was determined that the flow rate of the odorant carrier gas, length of the olfactory mucus surface, and the solubility of odorant molecules in the olfactory mucus should play important roles in determining the odor intensity for these odorants. The model predicts that, given adequate mucus surface for sorption, increase in the flow rate results in an increase in perceived odor intensity for the readily sorbed or highly soluble odorants (such as carvone) and a decrease in odor intensity for the poorly sorbed or insoluble odorants (such as octane). With a substantial decrease in the mucus surface for sorption, increase in the flow rate results in a decrease in perceived odor intensity for all odorants. The theoretical results show good agreement with various experimental data obtained from both psychophysical and electrophysiological studies of olfaction using animals and human subjects.Keywords:
Olfactory mucosa
Objectives Olfaction is frequently impaired in chronic rhinosinusitis with nasal polyps (CRSwNP) and often improves after endoscopic sinus surgery (ESS). Data about dynamics of olfactory changes after ESS are lacking, and little information is available concerning whether preoperatively administered glucocorticosteroids predict postoperative olfaction. Therefore, the aim of this study was to examine dynamics of olfaction after ESS in relation to the effect of preoperative administration of glucocorticosteroids in CRSwNP. Methods This prospective study included 52 CRSwNP patients (30 men, 22 women, mean age 54 ± 14 years) divided into a control group (n = 31) subjected to ESS without preoperative steroids and a treatment group (n = 21) receiving orally administered glucocorticosteroids preoperatively. Self‐ratings of olfaction and olfactory testing using the extended Sniffin’ Sticks test battery (threshold, discrimination and identification [TDI] score) were performed. Olfaction was measured preoperatively; after termination of glucocorticosteroid treatment (only treatment group); and 2 weeks, 1 month, and 3 months postoperatively. Results After glucocorticosteroids, TDI score significantly improved in 57% of patients, and olfactory function remained unchanged in 43%. In addition, improvement in TDI score after steroids and 3 months postoperatively were significantly correlated (r = 0.66, P = 0.01). Patients whose olfaction did not improve after glucocorticosteroids did not benefit from surgery. Regarding postoperative olfactory dynamics, TDI score reached its maximum 1 month postoperatively and decreased again approximately 3 months after surgery. Conclusion Glucocorticosteroids improved olfaction in CRSwNP comparable to surgery. In addition, changes in relation to steroids predicted olfactory outcome postoperatively. Regarding the olfactory dynamics, it could be demonstrated that olfactory function increased 1 month after surgery and decreased 3 months postoperatively. Level of Evidence 2 Laryngoscope , 130:1616–1621, 2020
Chronic Rhinosinusitis
Endoscopic sinus surgery
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Trigeminal Nerve
Olfactory nerve
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Olfactory mucosa
Histopathology
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This study investigated the role of prion infection of the olfactory mucosa in the shedding of prion infectivity into nasal secretions. Prion infection with the HY strain of the transmissible mink encephalopathy (TME) agent resulted in a prominent infection of the olfactory bulb and the olfactory sensory epithelium including the olfactory receptor neurons (ORNs) and vomeronasal receptor neurons (VRNs), whose axons comprise the two olfactory cranial nerves. A distinct glycoform of the disease-specific isoform of the prion protein, PrPSc, was found in the olfactory mucosa compared to the olfactory bulb, but the total amount of HY TME infectivity in the nasal turbinates was within 100-fold of the titer in the olfactory bulb. PrPSc co-localized with olfactory marker protein in the soma and dendrites of ORNs and VRNs and also with adenylyl cyclase III, which is present in the sensory cilia of ORNs that project into the lumen of the nasal airway. Nasal lavages from HY TME-infected hamsters contained prion titers as high as 103.9 median lethal doses per ml, which would be up to 500-fold more infectious in undiluted nasal fluids. These findings were confirmed using the rapid PrPSc amplification QuIC assay, indicating that nasal swabs have the potential to be used for prion diagnostics. These studies demonstrate that prion infection in the olfactory epithelium is likely due to retrograde spread from the olfactory bulb along the olfactory and vomeronasal axons to the soma, dendrites, and cilia of these peripheral neurons. Since prions can replicate to high levels in neurons, we propose that ORNs can release prion infectivity into nasal fluids. The continual turnover and replacement of mature ORNs throughout the adult lifespan may also contribute to prion shedding from the nasal passage and could play a role in transmission of natural prion diseases in domestic and free-ranging ruminants.
Vomeronasal organ
Olfactory mucosa
Olfactory marker protein
Olfactory ensheathing glia
Olfactory nerve
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Human brain
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Neuromorphic engineering
Antennal lobe
Olfactory nerve
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Abstract Olfactory dysfunction (OD) in Parkinson’s disease (PD) appears several years before the presence of motor disturbance. Olfactory testing has the potential to serve as a tool for early detection of PD, but OD is not specific to PD as it affects up to 20% of the general population. Olfaction includes an orthonasal and a retronasal components; in some forms of OD, retronasal olfactory function is preserved. We aimed to evaluate whether combined testing components allows for discriminating between PD-related OD and non-Parkinsonian OD (NPOD). The objective of this study is to orthonasal and retronasal olfactory function in PD patients and compare them to a NPOD group and to healthy controls. We hypothesized that this combined testing allows to distinguish PD patients from both other groups. We included 32 PD patients, 25 NPOD patients, and 15 healthy controls. Both olfactory components were impaired in PD and NPOD patients, compared with controls; however, NPOD patients had significantly better orthonasal scores than PD patients. Furthermore, the ratio of retronasal/orthonasal score was higher in PD than in both other groups. In the NPOD group, orthonasal and retronasal scores were significantly correlated; no such correlation could be observed in PD patients. In summary, PD patients seem to rely on compensatory mechanisms for flavor perception. Combined orthonasal and retronasal olfactory testing may contribute to differentiate PD patients from patients with NPOD.
Hyposmia
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Hyposmia
Anosmia
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The pre- and postnatal development of human olfaction is described. Data from animal experiments a partially reviewed as a base for understanding of the results of olfactory testing of babies and children. In rat fetuses the vomero-nasal-organ is used as detector of molecules in the amnion fluid. The perinatal aeration of the nasal cavity allows the adequate stimulation of the olfactory epithelium. The early postnatal olfaction is a brainstem function; later the olfactory cortical area are used for the discrimination between odorants. There are only a few investigations about the olfactory function in childhood, so that the testing of olfaction for detecting abnormal brain developments is just in the beginning.
Olfactory mucosa
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The olfaction is related to flow in the olfactory cleft. However, There is a lack of studies on the relationship between flow characteristics of the olfactory cleft and olfactory function. In this study, the anatomical structure of the olfactory cleft was reconstructed in three dimensions using the raw data obtained from the CT scans of sinuses of 32 enrolled volunteers. The Sniffin' Sticks test was used to examine the olfaction. We investigated the correlation between airflow parameters and olfactory function of the olfactory cleft in healthy adults by the computational fluid dynamics method. We found that three parameters, airflow, airflow velocity, and airflow ratio, were highly positively correlated with olfactory function. The mean pressure was not correlated with the olfactory function. Furthermore, there is the strongest correlation between air flow through the olfactory cleft and olfactory function. The correlation between the mean velocity in the anterior olfactory cleft region and olfaction was relatively poor, while the airflow velocity at the posterior olfactory cleft region was enhanced gradually. The correlation between the airflow ratio and olfaction was optimal in the initial position of superior turbinate. The flow parameters in the posterior olfactory cleft area were more stable.
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