Retronasal Olfaction Research Articles

Orthonasal and retronasal olfactory function in patients with chronic rhinosinusitis without nasal polyps undergoing endoscopic sinonasal surgery.

Olfactory dysfunction (OD) is a key symptom of chronic rhinosinusitis (CRS). Although extensively studied in CRS with nasal polyps (CRSwNP), OD in CRS without nasal polyps (CRSsNP) remains under-researched. This study aims to assess the prevalence of OD and its evolution in surgically naïve patients with CRSsNP undergoing endoscopic sinus surgery (ESS). This prospective study included 97 participants with CRSsNP (mean age, 46.5 years; 70.1% men) and 97 healthy controls (mean age, 46.5 years; 70.1% men). Participants underwent psychophysical evaluations of orthonasal (using the Sniffin' Sticks test) and retronasal olfaction (using powdered aromas) at enrolment and 6 months post-ESS. Out of 97 patients, 81 (83.5%) completed all assessments. At enrolment, 23 (28.4%) CRSsNP patients had OD based on composite threshold, discrimination, identification scores, compared with 7 (8.6%) controls (absolute % difference, 19.8% [95% CI, 8.2-31.4]). Retronasal olfactory function was also significantly worse in CRSsNP patients. Six months post-ESS, 30 patients (37.0%) experienced a clinically significant improvement in olfactory, whereas nonsignificant changes were observed in retronasal olfactory score, and 3.7% of patients experienced a deterioration of the olfactory function. In conclusion, although 37% of patients experienced a clinically significant improvement in their sense of smell following ESS, the overall prevalence of OD in this surgically naive population appears relatively low, especially when compared to that observed in patients with CRSwNP. Therefore, ESS may offer some benefits for enhancing orthonasal olfactory function, but the extent of these improvements appears to be limited.

Adherence to olfactory training improves orthonasal and retronasal olfaction in post-COVID-19 olfactory loss.

Olfactory loss (OL) has emerged as one of the most prevalent and debilitating symptoms of SARS-CoV-2 infection and long-COVID-19. The present prospective observational study aimed to evaluate the efficacy of olfactory training (OT) on orthonasal and retronasal olfactory function in a cohort of individuals with persistent post-COVID-19 OL. Participants with post-COVID-19 olfactory impairment underwent 4 months of OT, self-assessing their smell perception and undergoing comprehensive psychophysical evaluation of orthonasal and retronasal olfaction at baseline and after training. Orthonasal olfactory function was assessed using the extended Sniffin' Sticks test battery. Retronasal olfactory function was tested with powdered aromas. Among 114 participants with post-COVID-19 olfactory loss, adherence to OT was 60%. In adherents, the average increase in composite TDI score was 6.0 points compared to 2.6 points in non-adherents. Fifty-seven percent of adherent participants achieved a clinically significant improvement in TDI score (≥5.5 points), compared to 22% of non-adherents. In retronasal olfactory identification, 56% of adherents achieved a clinically significant improvement (≥4 points), compared to 16% of non-adherents. Adherence to a 4-month OT regimen can yield clinically meaningful improvements in both orthonasal and retronasal olfactory function among individuals with persistent post-COVID-19 olfactory dysfunction.

A practical test for retronasal odor identification based on aromatized tablets

BackgroundOlfactory perceptions elicited by odors originating from within the body (retronasal olfaction) play a crucial role in well-being and are often disrupted in various medical conditions. However, the assessment of retronasal olfaction in research and the clinical practice is impeded by the lack of commercially available tests and limited standardization of existing testing materials. New MethodThe novel ThreeT retronasal odor identification test employs 20 flavored tablets that deliver a standardized amount of odorous stimuli. The items represent common food- and non-food-related odors. ResultsThe ThreeT test effectively distinguishes patients with olfactory dysfunction from healthy controls, achieving a specificity of 86% and sensitivity of 73%. Its scores remain stable for up to 3 months (r=.79). Comparison with existing methodThreeT test exhibits a strong correlation with “Tasteless powders” measure of retronasal olfaction (r=.78) and classifies people into healthy and patient groups with similar accuracy. Test-retest stability of ThreeT is slightly higher than the stability of “Tasteless powders” (r=.79 vs r=.74). ConclusionsThreeT is suitable for integration into scientific research and clinical practice to monitor retronasal odor identification abilities.

Can humans smell tastants?

Although studies have shown that olfaction may contribute to the perception of tastant, literature is scarce or circumstantial, especially in humans. This study aims to (i) explore whether humans can perceive solutions of basic prototypical tastants through orthonasal and retronasal olfaction and (ii) to examine what volatile odor compounds (VOCs) underlie this ability. Solutions of 5 basic tastants (sucrose, sodium chloride, citric acid, monosodium glutamate [MSG], quinine) dissolved in water, and 2 fatty acids (oleic and linoleic acid) dissolved in mineral oil were prepared. Triangle discrimination tests were performed (n = 41 in duplicate) to assess whether the tastant solutions can be distinguished from blanks (solvents) through ortho- and retronasal olfaction. Participants were able to distinguish all tastant solutions from blank through orthonasal olfaction. Only sucrose, sodium chloride, oleic acid, and linoleic acid were distinguished from blank by retronasal olfaction. Ethyl dichloroacetate, methylene chloride, and/or acetone were identified in the headspace of sucrose, MSG, and quinine solutions but not in the headspace of water, sodium chloride, and citric acid solutions. Fat oxidation compounds such as alcohols and aldehydes were detected in the headspace of the oleic and linoleic acid solutions but not the mineral oil. We conclude that prototypical tastant solutions can be discriminated from water and fatty acid solutions from mineral oil through orthonasal olfaction. Differences in the volatile headspace composition between blanks and tastant solutions may have facilitated the olfactory discrimination. These findings can have methodological implications for future studies assessing gustatory perception using these prototypical taste compounds.

Taste and odor interactions after metabolic surgery.

Most patients report "taste" changes after undergoing metabolic surgeries. Yet, most studies that used validated sensory evaluation techniques, including ours, found no changes in perceived taste intensity from before to after surgery. However, we assessed participants with pure gustatory stimuli and after an overnight fast, which raises questions about whether patients' self-reported "taste" changes are due to conflating changes in retronasal smell/"flavor" with taste changes or whether they only manifest during the fed state. To investigate this, we conducted a cross-sectional study comparing sensory responses in women who underwent metabolic surgery 2 to 6 yr ago (n = 15) with 2 nonoperated control groups: one with a body mass index (BMI) equivalent (n = 15) and one with a healthy BMI (n = 15). Participants attended 2 sessions, one fed and one fasted. Using a sip-and-spit method, women tasted liquid samples containing gustatory and olfactory stimuli and puddings with varying fat content with and without nose clips. They used separate general labeled magnitude scales to rate their perceived intensity of taste, smell, flavor, and liking. Mixed ANOVAs indicated that the surgery and BMI equivalent groups rated retronasal smell intensity of coffee stronger than the healthy BMI group (P ≤ 0.015). However, there were no differences in taste/flavor intensity or liking ratings among groups. Additionally, feeding conditions did not significantly affect perceived intensity ratings. Our findings suggest that changes in the sensory-discriminatory component of taste or taste-odor interactions are not significant contributors to dietary modifications following metabolic surgery.

Heterogeneous Damage to the Olfactory Epithelium in Patients with Post-Viral Olfactory Dysfunction.

Post-viral olfactory dysfunction (PVOD) is a neurogenic disorder caused by a common cold virus. Based on the homology of deduced amino acid sequences, olfactory sensory neurons (OSNs) in both mice and humans express either class I or class II odorant receptor genes encoding class I and class II OSNs. The purpose of this study was to determine whether OSN damage in PVOD occurs uniformly in both neuron types. The characteristics of PVOD patients were compared with those of patients with chronic rhinosinusitis (CRS) or post-traumatic olfactory dysfunction (PTOD). Briefly, subjects underwent orthonasal olfaction tests using five different odors (T&T odors) and a retronasal olfaction test using a single odor (IVO odor). The regions in the mouse olfactory bulb (OB) activated by the T&T and the IVO odors were also examined. Multivariate analysis of 307 cases of olfactory dysfunction (PVOD, 118 cases; CRS, 161 cases; and PTOD, 28 cases) revealed that a combination of responses to the IVO odor, but not to the T&T odors, is characteristic of PVOD, with high specificity (p < 0.001). Imaging analysis of GCaMP3 mice showed that the IVO odor selectively activated the OB region in which the axons of class I OSNs converged, whereas the T&T odors broadly activated the OB region in which axons of class I and class II OSNs converged. A response to T&T odors, but not IVO odor, in PVOD suggests that class I OSNs are injured preferentially, and that OSN damage in PVOD may occur heterogeneously in a neuron-type-dependent manner.

Enhancing Olfactory Loss in COVID-19: The Impact of Body Position

Objective: To understand that COVID-19-induced hyposmia may fluctuate with spatial position. Introduction: COVID-19-induced hyposmia, exacerbated by supination, has yet to heretofore been described. Methods: Case Study: A 52-year-old right-handed woman was ansate until two years before presentation when she developed cold symptoms and sudden onset of loss of smell and taste, with a positive Reverse Transcription-Polymerase Chain Reaction test for COVID-19. Over three weeks, her smell and taste gradually returned to 85% of normal. She reported that her smell and taste would markedly worsen when she would lie down, to 30% of normal, but would improve with standing, moving, and sitting. Even reclining for a short nap would cause her sense of smell to drop, requiring her to stand for hours before her smell would recover, which caused her to fear sleeping and forced her to move around constantly. She markedly altered her lifestyle because of her fear of sleeping and assiduously avoided lying down: when so overwhelmed by tiredness that she must sleep, she would sleep sitting up. Results: Chemosensory Testing: Olfaction: Brief Smell Identification Test: 9 (normosmia). Alcohol Sniff Test: 3 (anosmia). Dirhinus amyl (pentyl) acetate Test: -7.0 (hyperosmia). Retronasal Olfaction: Retronasal Index: 8 (normosmia). Gustation: Phenylthiocarbamide Taste Test: 10 (normogeusia). Discussion: Despite cerebral autoregulation, recumbency may function to decrease venous return, altering calcium concentrations and hence olfactory ability. In the supine orientation, intrathoracic pressure increases, thus mimicking the Valsalva maneuver. This further increases intracranial pressure, decreases cerebral blood flow, and increases cerebral carbon dioxide. Perhaps this causes increased gamma-aminobutyric acid, an inhibitory neurotransmitter within the olfactory bulb, which reduces associated olfactory ability. Peradventure assuming the supine position induces general relaxation and stage. One sleep. Sleep reduces the intensity of perceptual experiences of all the senses, including the olfactory sense [1]. On the other hand, the supine and relaxed state may induce a positive effect. Based on Wolpe's reciprocal inhibition principle, such a relaxed effect causes fear inhibition, whereby there cannot be coexistent simultaneous opposite emotions [2]. Since fear has been demonstrated to improve olfactory ability, assuming the supine position induces relaxation and thus reduces fear-induced increased olfactory ability (Yakov, 2013; Keedwel, 2005). On the other hand, assuming the supine position may induce a kinesthetic distraction, changing the focus of attention away from chemosensation to a change in position. Lying in the lateral decubitus position possibly causes a modification in the olfactory cycle with greater engorgement in the inferiorly situated nostril, which may have a lesser olfactory ability [1]. In those with olfactory deficits after COVID-19 or other conditions, a reduced olfactory ability with lying down may have significant health risks. Further investigation into the impact of position on those with olfactory deficits from all sources, including COVID-19, is warranted.

Correlations between gustatory, trigeminal, and olfactory functions and nasal airflow

PurposeTo determine the relationship of chemosensory screening and nasal airflow tests among the same set of participants, and to determine other factors that are related to the outcomes of these tests.MethodsParticipants had no chemosensory complaints. Structured medical history was taken. Participants underwent 5 screening tests: q-sticks (orthonasal olfaction), q-powders (retronasal olfaction), trigeminal lateralization test, taste sprays, and peak nasal inspiratory flow (PNIF). Ratings of smell/taste ability and nasal airflow were obtained using visual analogue scales (VAS). Composite sinusitis symptoms and significance of olfaction questionnaire scores were also determined.ResultsFour hundred participants were included in the study, 156 men, 244 women; aged 18–82 years (mean: 46). The q-powders and taste spray scores were weakly positively correlated with all the other chemosensory tests and PNIF. However, chemosensory test scores were not correlated with VAS, composite sinusitis symptoms, and significance of olfaction questionnaire scores. Various tests showed significant decrease starting at specific ages (in years, PNIF and trigeminal lateralization: 40, q-powders: 60, and q-sticks: 70).ConclusionChemosensory screening tests and self-rated chemosensory function showed no correlation in participants without chemosensory complaints. In addition, gustatory function appeared to be correlated with olfactory and trigeminal function but also with nasal airflow, and nasal airflow was related not only to olfactory but also to trigeminal and taste function. Over all, the results suggest that chemosensory functions (orthonasal olfactory, trigeminal, retronasal olfactory, gustatory) and nasal airflow are correlated with each other, which we propose may be possibly mediated, at least in part, through central nervous system interactions.

COVID-19 Induced Elimination of First Taste Phenomenon (P5-10.002)

<h3>Objective:</h3> Correlation of First Taste Phenomenon elimination with COVID-19 infection <h3>Background:</h3> First Taste Phenomenon, whereby perception of flavor occurs at first bite and then dissipates is associated with chemosensory loss (Hirsch, 2018). Elimination of this Phenomenon associated with COVID-19 has not been described. <h3>Design/Methods:</h3> This 62 year old right handed man presented with upper respiratory tract infection induced chemosensory loss that resolved after treatment of 9 g of phosphatidylcholine. His smell declined to 50% of normal. Taste was lost but he retained his first taste phenomenon. He tested positive for COVID-19 presenting with loss of chemosensation which did not resolve despite treatment with nirmatrelvir/ ritonavir. Symptoms of COVID-19 improved after infection resolution, but First Taste Phenomenon never returned. <h3>Results:</h3> Neurological Abnormalities: Gustatory Testing: Taste threshold: Hypogeusia of 10–30% to sucrose. Electrogustometry Testing: left (L) posterior tongue: 34 (abnormal), right (R) posterior tongue: 34 (abnormal), L anterior tongue: 34 (abnormal), R anterior tongue: 30 (abnormal). Right palate: &gt;32 (abnormal), left palate: &gt;32 (abnormal). Taste Quadrant Testing: Front to back: decreased anteriorly to Sodium Chloride, Sucrose, Quinine Hydrochloride. <h3>Conclusions:</h3> The semiology of First Taste Phenomenon includes Classic First Taste Syndrome with full flavor of food followed by rapid, less than 1 minute, decrement in flavor of food (Hirsch, 2018). Retronasal smell inducing flavor perception as nidus to First Taste Syndrome (Djordjevic, 2004) could be eliminated after COVID-19 infection, which reduces retronasal smell, and induce perceived taste loss (Parma, 2020). This First Taste Phenomenon attributes to temporal decrement in saliva as a consequence of persisted mandibulation-reducing taste threshold sensitivity (Weiffenbach, 1995). COVID-19 worsens such hyposalivation (da Mota Santana, 2021). COVID-19 may eliminate first taste and cause CNS dysfunction via ACE type 2 taste receptor cells dysfunction, (Mastrangelo, 2021) and cytokine storm respectively (Hintschich, 2021). Those with preexisting chemosensory dysfunction, association of COVID on remaining chemosensation is warranted. <b>Disclosure:</b> Miss Birwatkar has nothing to disclose. Mrs. Kalita has nothing to disclose. Dr. Hirsch has nothing to disclose.

Ortho‐ and Retronasal stimulations with specific food odours: Hedonic and familiarity ratings are related to chemosensory pleasure scale (CPS) scores

AbstractVolatile compounds can reach olfactory epithelium though the nose (orthonasal olfaction) or the mouth (retronasal olfaction). Although differences have been found between these two pathways in terms of odour sensitivity and identification, few studies have examined ortho‐ and retronasal differences taking into consideration the three main dimensions of olfactory perception (i.e. hedonicity, intensity and familiarity). Olfactory perception, and particularly odour hedonic perception, is influenced by several factors such as sex or age. Another variability factor worth considering, especially regarding food‐related odours, is the ability to experience pleasure simulated by smell or taste, which can be measured with the Chemosensory Pleasure Scale (CPS). Thus, the aims of this study were (1) to compare odour sensory ratings in response to ortho‐ and retronasal presentation and (2) to examine the relationship between CPS scores and odour sensory ratings in ortho‐ and retronasal pathways. Participants rated ten food odours in ortho‐ and retronasal conditions using visual analogue scales and were divided into two subgroups based on the median CPS score (CPS+ and CPS− groups). Results revealed similar sensory responses to food odours between ortho‐ and retronasal pathways for the three main dimensions of olfactory perception. Interestingly, when CPS scores were considered, clear differences in odour familiarity and hedonicity were shown, particularly for the retronasal pathway (i.e. odours were perceived as more pleasant and more familiar in CPS+ group than in CPS− group). Overall, these findings suggest that differences in odour perception between ortho‐and retronasal pathways may be related to specific individual characteristics such as chemosensory hedonic capacity.

Too Sweet to Eat: Delusional Hypergeusia

AbstractIntroductionDelusional hypergeusia has not heretofore been reported.Methods: Case reportA 62-year-old right-handed woman described a plethora of complaints after exposure to a solvent aroma, including headaches, diffuse weakness, fatigue, hallucinated smells and tastes, burning mouth syndrome, and panic attacks. The apogee of her symptoms was that salty taste was 800% of normal, making food taste disgustingly salty. She was unable to tolerate potato chips, pizza, spaghetti sauce, Coca Cola, root beer, Sprite, 7 Up, and even bottled water. Sugar was also too sweet, 600% of normal. Foods which were unbearably sweet included cookies, sugar, and breakfast cereals. Sour and bitter were normal.ResultsAbnormalities in Neurological Examination: Mental Status Examination: hyperverbal, loud, overly inclusive, irritable with pressured speech; disheveled, racing thoughts, and tangential. Motor Examination: Drift Test: right pronator drift with right abductor digiti mini sign. Gait Examination: heel walking with bilateral decreased arm swing. Reflexes: bilateral quadriceps femoris 3+, positive left (L) Hoffman’s reflex. Chemosensory Testing: Olfaction: Brief Smell Identification Test: 12 (normosmia). Retronasal Olfactory Testing: Retronasal Smell Index: 1 (Anosmia). Gustatory Testing: Propylthiouracil Disc Taste Test: 10 (normogeusia). Waterless Empirical Taste Test: sweet: 4, sour: 3, salty: 7, bitter: 5, brothy: 0, total: 30 (ageusia to umami, otherwise normogeusia). Neuropsychiatric Testing: Go-No-Go Test: 2/6 (abnormal).DiscussionPerhaps hypergeusia may not have been true hypergeusia but a misperception of retronasal smell associated hyperosmia with physiologic synesthesia manifested as taste. Peradventure, the perceived hypergeusia, is just one component of a generalized delusional paradigm, where many sensory perceptions are intensified. The perceived delusional hyperosmia may be intensification of the sensory misperception due to an underlying dysgeusia. This may represent a variant of the two-factor hypothesis of delusions whereby a distorted sensory perception is then misrepresented in a delusion. Dysfunction of the right hemisphere, which normally acts to censor the left, allows the delusion to manifest. While two different anatomical abnormalities (one left and one right hemisphere) have been postulated to be the foundation of such delusions, it is distinctly possible that a single lesion of the inferior parietal lobule may be sufficient for both sensory distortions to be produced as well as loss of inhibition of delusional interpretation of distorted sensation of the frontal lobe by the right parietal lobe, yclept the sensorialist hypothesis. In those who present with hypergeusia, search for delusional origin is warranted and in those who present with delusions, query as to perceived hypergeusia may be revealing.FundingNo Funding

Treatment of Olfactory Disorders After SARS - CoViD 2 Virus Infection.

The benefit of a nasal corticosteroid in the treatment of persistent post-infectious smell disorders is not as clear in previous studies as is assumed for olfactory training. This study would therefore like to describe the treatment strategies using the example of a persistent olfactory dysfunction as a result of a proven infection with SARS-CoViD-2-virus. Twenty patients (average age of 33.9 ± 11.9years) with hyposmia were included in this study from December 2020 to July 2021. Every second patient received additionally a nasal corticosteroid. The two resulting randomized groups of equal size were screened with the TDI test, a 20-item taste powder test for the assessment of retronasal olfaction and otorhinolaryngological examination. The patients were asked to train twice daily using a standardized odor training kit and followed up after 2months and 3months, respectively. We documented a significant overall improvement in olfactory ability over the investigation period in both groups. While the TDI score steadily increased on average under the combination therapy, the rise under olfactory training alone was initially steeper. This short-term interaction effect over mean two months was not statistically significant. According to Cohen, however, a moderate effect (eta2 = 0.055, Cohen`s d = 0.5) can still be assumed. This effect could be explained by a possibly higher compliance at the beginning of the sole olfactory training due to the lack of further drug treatment offers. When the training intensity decreases, the recovery of the sense of smell stagnates. Adjunctive therapy ultimately outweighs this short-term benefit. The results reinforce the recommendation of early and consistent olfactory training on patients with dysosmia due to COVID-19. For continuous improvement of the sense of smell, an accompanying topical treatment seems at least to be worth consideration. The results should be optimized with larger cohorts and using new objective olfactometric methods.

Decreased retronasal olfaction and taste perception in obesity are related to saliva biochemical and microbiota composition

Understanding the individual factors that modulate flavor perception is a central issue for the development of personalized diets strategies to fight obesity. This study aimed to investigate differences in flavor perception between adults with normal weight and those with obesity, as well as some potential biological factors related to these differences. To do that, liking and flavor perception intensity were measured against retronasal olfactory (pineapple, butter, tropical and chocolate) and taste attributes (sweetness, umami and bitter) in 77 individuals grouped as normalweight or obese, according to their body mass index (BMI). Unstimulated saliva was collected from all participants and characterized in terms of salivary flow, total protein content, total antioxidant capacity, total esterase activity and bacterial composition through 16S rDNA amplicon sequencing. The results showed that participants displayed differences in flavor perception according to their BMI group. Thus, the group with obesity showed significant lower liking and intensity scores for low calorie related food aroma (pineapple and tropical), lower taste intensity scores for sweet and umami, and a higher acceptability for umami than the group with normal weight. Significant differences between BMI groups were observed for salivary biochemical variables and specific bacterial taxa, some of which were significantly correlated to flavor intensity. This work suggests for the first time the existence of an oral-brain axis that might contribute to the development or perpetuation of obesity, which opens new and interesting avenues of research.

Retronasal Olfaction Stimulation and its Implication for Health: A Commentary on the Available Evidence.

Retronasal olfaction is the perception of odors emanating from the oral cavity during eating and drinking, as opposed to orthonasal olfaction, which occurs during sniffing (Rozin, 1982). The retronasal olfactory pathway contributes to the perceived flavor of foods and drinks. Retronasal and orthonasal function are distinct physiologic processes, with evidence identifying divergent neurobiological mechanisms (Small et al., 2005). A diminished quality of life has been reported from dysfunctions of both retronasal and orthonasal olfaction, especially when adversity occurs with the identification of food and drinks (Oleszkiewicz et al., 2019). Until recently, interest in retronasal olfaction extended only to food-related questions, with its clinical significance being limited to a means for detecting malingerers in a medicolegal setting (Hummel et al., 1999). With the development of olfactory sciences and the field of aromachology, health implications that may arise from targeted stimulation of the retronasal olfactory pathway have come into the forefront of research.

Scent-Triggered Cerebral Activity: How Retronasal Olfaction Influences the Food-Reward Feedback System

The flavour of foods and drinks is influenced by perceptual interactions between genuine taste and odour active compounds that are sensed retronasally. Interdisciplinary teams of plant and sensory experts have identified specific flavour changes that influence overall favour profiles. Currently, it is unknown how retronasal sensations might vary with measures of taste phenotype and taste function, and how such differences might influence liking and intake of certain foods and drinks over others. Given that neural response depends not only on the type of stimuli, but also in large part on the cognitive context, focus and state of the individual, a conclusive determination of the food reward response triggered by retronasal olfaction is warranted.

Enhancement of taste by retronasal odors in patients with Wolfram syndrome and decreased olfactory function.

Wolfram syndrome is a rare disease characterized by diabetes, neurodegeneration, loss of vision, and audition. We recently found, in a young sample of participants (mean age 15 years), that Wolfram syndrome was associated with impairment in smell identification with normal smell sensitivity and whole-mouth taste function. However, these senses were assessed separately, and it is unknown whether smell-taste interactions are altered in Wolfram syndrome, which was the focus of this study. Participants with Wolfram syndrome (n = 36; 18.2 ± 6.8 years) and sex-age-equivalent healthy controls (n = 34) were assessed with a battery of sensory tests. Using sip-and-spit methods, participants tasted solutions containing gustatory and olfactory stimuli (sucrose with strawberry extract, citric acid with lemon extract, sodium chloride in vegetable broth, and coffee) with and without nose clips, and rated perceived taste and retronasal smell intensities using the generalized Labeled Magnitude Scale. Participants also completed n-butanol detection thresholds and the University of Pennsylvania Smell Identification Test (UPSIT). Retronasal smell increased taste intensity of sucrose, sodium chloride, and coffee solutions similarly in both groups (P values <0.03). Compared with the control group, participants in the Wolfram group had lower UPSIT scores and reduced smell sensitivity, retronasal intensity, and saltiness (P values <0.03), but rated other taste intensities similarly when wearing the nose clip. Despite impairments in orthonasal smell identification, odor-induced taste enhancement was preserved in participants with Wolfram syndrome who still had some peripheral olfactory function. This finding suggests that odor-induced taste enhancement may be preserved in the presence of reduced olfactory intensity.

Impact of Metabolic Syndrome on Retronasal Olfaction

As rates of metabolic syndrome (MS) rise globally, it is unclear how and if the risk factors associated with this condition impact flavor perception via the retronasal pathway, which is critical for experiencing the flavor of foods and drinks. This commentary discusses existing literature on the possible impacts of MS on retronasal olfaction by examining primary diagnostic criteria, including hypertension, hyperglycemia, hypertriglyceridemia, hypoalphalipoproteinemia, and excess visceral adipose tissue. Risk factors for MS including hypertension, obesity, and hyperglycemia appear to have a negative impact on the sensitivity of retronasal olfaction. Although most of the work cited in this communication affirms that MS does negatively affect the functionality of the olfactory system, it is important to note that research is divided on this determination. Although retronasal dysfunction is not considered a life threating condition, it drastically changes the landscape of sensory information perceived and impacts an individual’s quality of life. Further clinical research on the impact of MS on retronasal olfaction is warranted to provide insights into the intricacies of these pathways.

Chemosensory Functions After Glossectomy-A Cross-Sectional Pilot Study.

To evaluate potential interactions and compensatory mechanisms of subjectively impaired taste function with ortho- and retronasal olfaction after glossectomy. In this cross-sectional pilot study, chemosensory functions were assessed in 25 patients with tongue carcinomas after glossectomy. The orthonasal-, retronasal-, and gustatory functions were tested with a mean time of 25 months after surgery with the Sniffin' Sticks odor identification test kit (ISST), the Candy Smell-27 test (CST-27) and the Taste strip test (TST). Visual analog scales (VAS) were additionally used for self-assessment of taste, flavor perception, and odor ranging from 0 (no perception) to 10 (excellent perception) and further correlated with our psychophysical evaluated outcome measures. The TST, ISST, and CST-27 tests revealed that only eight (32%) and 13 (52%) glossectomy patients had normal taste and orthonasal function, e 21 (84%) patients showed normal retronasal function. Importantly, neither extent of resection and reconstruction nor prior radiotherapy affected chemosensory functions. Contrary, 20 (80%) patients rated their taste and flavor perception as acceptable (VAS >5). Results of the TST, ISST, and CST-27 tests did not correlate with the equivalent self-assessments of taste (p=0.260, r=0.234), odor (p=0.588, r=-0.114), and flavor (p=0.728, r=0.073) perception. There was a significant discrepancy between self-perception of taste and flavor and assessed gustatory function after glossectomy. A contribution of the intact retronasal olfactory system could be a possible explanation of our results. 4 Laryngoscope, 133:375-382, 2023.

Olfactory rehabilitation via retronasal olfaction using atracheoesophageal voice prosthesis after total laryngectomy. German version

Despite the variety of existing methods for olfactory rehabilitation after total laryngectomy, olfactory disability remains one of the main factors limiting quality of life for laryngectomees. Considering theneed for asocially acceptable rehabilitation method that is suitable for everyday use, this study sought to elucidate whether retronasal olfaction during phonation through atracheoesophageal voice prosthesis is possible. The odor identification of 22laryngectomees was assessed using the Sniffin' Sticks test battery (12 odors), while performing an established method of olfactory rehabilitation-"polite yawning"-or while transnasal expiration or phonation through the tracheoesophageal fistula (TF). To facilitate the latter, anovel Expiratory Nasal Airflow M‑Maneuver (ENAMM) was developed. All 21non-anosmic laryngectomees included in the study were able to identify odors retronasally. While only 6of 22patients (27.3%) could perform the nasal expiration through the TF, all patients could easily perform phonation using ENAMM after proper instruction. The odor identification scores with the ENAMM technique did not statistically differ from ones with "polite yawning" (5.4 ± 3.1 vs. 6.4 ± 3.2, p = 0.279). The ENAMM was easy to learn and showed atendency of increasing olfactory scores over time, possibly due to a learning effect. Study results show that retronasal olfaction using avoice prosthesis after total laryngectomy is possible and suggest the potential of ENAMM as amethod of olfactory rehabilitation for laryngectomy patients.

Characterization of Retronasal Airflow Patterns during Intraoral Fluid Discrimination Using a Low-Cost, Open-Source Biosensing Platform.

Nasal airflow plays a critical role in olfactory processes, and both retronasal and orthonasal olfaction involve sensorimotor processes that facilitate the delivery of volatiles to the olfactory epithelium during odor sampling. Although methods are readily available for monitoring nasal airflow characteristics in laboratory and clinical settings, our understanding of odor sampling behavior would be enhanced by the development of inexpensive wearable technologies. Thus, we developed a method of monitoring nasal air pressure using a lightweight, open-source brain–computer interface (BCI) system and used the system to characterize patterns of retronasal airflow in human participants performing an oral fluid discrimination task. Participants exhibited relatively sustained low-rate retronasal airflow during sampling punctuated by higher-rate pulses often associated with deglutition. Although characteristics of post-deglutitive pulses did not differ across fluid conditions, the cumulative duration, probability, and estimated volume of retronasal airflow were greater during discrimination of perceptually similar solutions. These findings demonstrate the utility of a consumer-grade BCI system in assessing human olfactory behavior. They suggest further that sensorimotor processes regulate retronasal airflow to optimize the delivery of volatiles to the olfactory epithelium and that discrimination of perceptually similar oral fluids may be accomplished by varying the duration of optimal airflow rate.