Menthol: effects on nasal sensation of airflow and the drive to breathe

Chief Complaint: Nasal Congestion

Nasal obstruction is the subjective perception and objective state of insufficient airflow through the nose. Nasal congestion, conversely, describes a state of not just inadequate airflow or obstructive phenomena but also pressure- and mucus-related states to the patient. Nasal receptors belonging to the transient receptor potential (TRP) protein family mediate the sense of nasal patency via the trigeminal nerve. The transient receptor potential melastatin-8 (TRPM8) responds to temperatures around 8°C to 22°C, and is stimulated by menthol and other cooling agents. The radiant effects of airflow create heat loss to activate these receptors and humans perceive this as nasal patency rather than the direct detection of airflow. The thermovascular state of the mucosa, in conditions such as rhinitis, influence TRPM8 activation. Nasal endoscopy can show signs of rhinitis and should be considered an essential part of the workup of nasal congestion. Efforts to relieve nasal congestion need to manage the mucosal state and surgery needs to ensures that the nasal cavity mucosa is exposed to the cooling effects of airflow rather than simply creating a passage to the nasopharynx.

Menthol mouth rinsing and performance in elite football referees in the heat: A study protocol for a randomized crossover trial

Background

Within professional European competitions, matches can be played in extreme environmental temperatures, ranging from -5 °C to +30 °C in different countries. Furthermore, the World Cups are usually played in the summer months, when temperatures can exceed 35 °C, increasing physiological stress. Practical and cost-effective cooling strategies may be implemented to help players and referees to cope with exercising in the heat. No study has evaluated the effect of non-thermal internal cooling techniques regarding performance responses on elite football referees, so far. This study aims to analyse the effects of a menthol mouth rinse regarding physical, physiological, and perceptual performance in elite male football referees, during a 90-min football protocol in the heat.

Methods

At least thirteen male football referees will be recruited to perform two intermittent football protocols, separated by no less than 7 days. After passing the eligibility criteria, the participants will be randomly assigned to 1 of 2 beverages: (1) intervention - menthol solution 0.01% and (2) placebo - noncaloric berry-flavored solution, both at room temperature. The beverages will be given before warm-up (pre-cooling) and at the half-time (per-cooling). The trials will follow a randomized counterbalanced crossover design, single blinded, and will take place in indoor facilities, with Wet Bulb Globe Temperature (WBGT) > 30 °C, at the same time of the day to control for circadian variations.

Impact of the project

The results of this study are expected to determine whether mouth rinsing a menthol solution before and during a football exercise protocol performed in the heat will alter perceptual measures and help ease physiological strain and attenuate performance decrements in elite male football referees, comparing to a non-cooling strategy. Thus, we can be closer to defining nutritional strategies of internal cooling that may be an advantage for the performance of the football referees in the heat.

Trial registration

www.ClinicalTrials.gov NCT05632692 registered on 20 November 2022.

Distinguishing science from pseudoscience in commercial respiratory interventions: an evidence-based guide for health and exercise professionals

Respiratory function has become a global health priority. Not only is chronic respiratory disease a leading cause of worldwide morbidity and mortality, but the COVID-19 pandemic has heightened attention on respiratory health and the means of enhancing it. Subsequently, and inevitably, the respiratory system has become a target of the multi-trillion-dollar health and wellness industry. Numerous commercial, respiratory-related interventions are now coupled to therapeutic and/or ergogenic claims that vary in their plausibility: from the reasonable to the absurd. Moreover, legitimate and illegitimate claims are often conflated in a wellness space that lacks regulation. The abundance of interventions, the range of potential therapeutic targets in the respiratory system, and the wealth of research that varies in quality, all confound the ability for health and exercise professionals to make informed risk-to-benefit assessments with their patients and clients. This review focuses on numerous commercial interventions that purport to improve respiratory health, including nasal dilators, nasal breathing, and systematized breathing interventions (such as pursed-lips breathing), respiratory muscle training, canned oxygen, nutritional supplements, and inhaled L-menthol. For each intervention we describe the premise, examine the plausibility, and systematically contrast commercial claims against the published literature. The overarching aim is to assist health and exercise professionals to distinguish science from pseudoscience and make pragmatic and safe risk-to-benefit decisions.

Impact of trigeminal and/or olfactory nerve stimulation on measures of inspiratory neural drive: Implications for breathlessness

The perception of breathlessness is mechanistically linked to the awareness of increased inspiratory neural drive (IND). Stimulation of upper airway cold receptors on the trigeminal nerve (TGN) with TGN agonists such as menthol or cool air to the face/nose has been hypothesized to reduce breathlessness by decreasing IND. The aim of this systematic scoping review was to identify and summarize the results of studies in animals and humans reporting on the impact of TGN stimulation or blockade on measures of IND. Thirty-one studies were identified, including 19 in laboratory animals and 12 in human participants. Studies in laboratory animals consistently reported that as TGN activity increased, measures of IND decreased (e.g., phrenic nerve activity). In humans, stimulation of the TGN with a stream of cool air to the face/nose decreased the sensitivity of the ventilatory chemoreflex response to hypercapnia. Otherwise, TGN stimulation with menthol or cool air to the face/note had no effect on measures of IND in humans. This review provides new insight into a potential neural mechanism of breathlessness relief with selected TGN agonists.

Nasal Airway Function After Prophylactic Intranasal Surgery for Excessive Maxillary Superior Repositioning: A Retrospective Cohort Study Using the Nasal Obstruction Symptom Evaluation Scale

PURPOSE

The purpose of this study is to evaluate the degree of nasal airway function after simultaneous intranasal corrective surgery and bimaxillary surgery in patients with excessive superior maxillary repositioning.

MATERIALS AND METHODS

A retrospective cohort study was conducted on consecutive LeFort I superior repositioning patients who also underwent simultaneous intranasal surgery to prevent airway obstruction between 2015 and 2019. The Nasal Obstruction Symptom Evaluation (NOSE) scale was administered to all participants before the operation and after 1 year.

RESULTS

Fifteen patients (n=12 females; n=3 males) among 440 bimaxillary orthognathic surgery patients were enrolled with inclusion criteria of maxillary impaction between 8 and 12 mm. All subjects underwent at least LeFort I osteotomy, septoplasty, bilateral inferior turbinectomy, and bilateral sagittal split osteotomy. Two patients received custom-made total joint prosthesis. The primary outcome variable investigated was nasal function. The mean preop Nasal Obstruction Symptom Evaluation score was 24.33 and the mean postop score was 5.

CONCLUSIONS

Intranasal procedures performed simultaneously with 8 mm or more maxillary impaction improves postoperative functional outcome in terms of nasal airway patency and breathing. Partial inferior turbinectomies and septoplasty should be performed consistently to avoid nasal obstruction if the impaction of upper jaw exceeds 8 mm.

Essential Oils and COVID-19

Herbal products are a major source of herbal medicines and other medicines. Essential oils have shown various pharmacological activities, such as antiviral activity, and therefore are proposed to have potential activity against SARS-CoV-2. Due to their lipophilicity, essential oils can easily penetrate the viral membrane and cause the viral membrane to rupture. In addition, crude essential oils usually have many active constituents that can act on different parts of the virus including its cell entry, translation, transcription, and assembly. They have further beneficial pharmacological effects on the host's respiratory system, including anti-inflammatory, immune regulation, bronchiectasis, and mucolytics. This review reported potential essential oils which could be promising drugs for COVID-19 eradication. Essential oils have many advantages because they are promising volatile antiviral molecules, making them potential drug targets for the prevention and treatment of COVID-19, whether used alone or in combination with other chemotherapeutic drugs. The aim of the current review is to shed light on the potential essential oils against enveloped viruses and their proposed activity against SARS-CoV-2 which is also an enveloped virus. The objectives were to present all data reflecting the promising activities of diverse essential oils against enveloped viruses and how they could contribute to the eradication of COVID disease, especially in indoor places. The data collected for the current review were obtained through the SciFinder database, Google scholar, PubMed, and Mendeley database. The data of the current review focused on the most common essential oils which are available in the pharmaceutical market and showed noticeable activities against enveloped viruses such as HSV and influenza.

Reference equations for oscillometry and their differences among populations: a systematic scoping review

Respiratory oscillometry is gaining global attention over traditional pulmonary function tests for its sensitivity in detecting small airway obstructions. However, its use in clinical settings as a diagnostic tool is limited because oscillometry lacks globally accepted reference values. In this scoping review, we systematically assessed the differences between selected oscillometric reference equations with the hypothesis that significant heterogeneity existed between them. We searched bibliographic databases, registries and references for studies that developed equations for healthy adult populations according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. A widely used Caucasian model was used as the standard reference and compared against other models using Bland-Altman and Lin's concordance correlational analyses. We screened 1202 titles and abstracts, and after a full-text review of 67 studies, we included 10 in our analyses. Of these, three models had a low-to-moderate agreement with the reference model, particularly those developed from non-Caucasian populations. Although the other six models had a moderate-to-high agreement with the standard model, there were still significant sex-specific variations. This is the first systematic analysis of the heterogeneity between oscillometric reference models and warrants the validation of appropriate equations in clinical applications of oscillometry to avoid diagnostic errors.

Menthol Mouth Rinsing Maintains Relative Power Production during Three-Minute Maximal Cycling Performance in the Heat Compared to Cold Water and Placebo Rinsing

Previous menthol studies have demonstrated ergogenic effects in endurance-based activity. However, there is a need for research in sports whose physiological requirements exceed maximal aerobic capacity. This study assessed the effects of 0.1% menthol mouth-rinsing upon a modified three-minute maximal test in the heat (33.0 ± 3.0 °C; RH 46.0 ± 5.0%). In a randomised crossover single blind placebo-controlled study, 11 participants completed three modified maximal tests, where each trial included a different mouth rinse: either menthol (MEN), cold water (WAT) or placebo (PLA). Participants were asked to rate their thermal comfort (TC), thermal sensation (TS) and rating of perceived exertion (RPE) throughout the test. Heart rate, core temperature, oxygen uptake (VO₂), ventilation (VE) and respiratory exchange ratio (RER) were monitored continuously throughout the test, alongside cycling power variables (W; W/kg). A blood lactate (BLa) level was taken pre- and post- test. Small to moderate effects (Cohen's d and accompanying 90% confidence intervals) between solutions MEN, WAT and PLA were observed towards the end of the test in relation to relative power. Specifically, from 75-105 s between solutions MEN and WAT (ES: 0.795; 90% CI: 0.204 to 1.352) and MEN and PLA (ES: 1.059; 90% CI: 0.412 to 1.666), this continued between MEN and WAT (ES: 0.729; 90% CI: 0.152 to 1.276) and MEN and PLA (ES: 0.791; 90% CI: 0.202 to 1.348) from 105-135 s. Between 135-165 s there was a moderate difference between solutions MEN and WAT (ES: 1.058; 90% CI: 0.411 to 1.665). This indicates participants produced higher relative power for longer durations with the addition of the menthol mouth rinse, compared to cold water or placebo. The use of menthol (0.1%) as a mouth rinse showed small performance benefits for short duration high intensity exercise in the heat.

The prevalence of complementary and alternative medicines (CAM) usage among allergic rhinitis patients in Malaysia

PURPOSE

We conducted this study to estimate the prevalence of complementary and alternative medicines (CAM) usage among allergic rhinitis (AR) patients in Malaysia and understand the practice of CAM usage among them. We also included a literature review on the commonly used CAM for AR.

METHODS

A cross-sectional study which included a questionnaire-based study and information of allergic rhinitis from patient's clinic records. Patients with AR who attended the ORL-HNS department in Hospital Universiti Sains Malaysia and Hospital Sultanah Aminah, Malaysia were enrolled after consented, on a first-come first-serve basis as convenience sampling from July 2020 until February 2021. A pre-tested self-administered, 16-item questionnaire in Malay language was distributed to the participants. The questionnaire consists of a set of 16 questions with subsets to enquire about the sociodemographic data and pattern of usage of CAM and its effectiveness.

RESULTS

372 patients were enrolled in this study consisting of 217 (58.3%) female and 155 (41.7%) male patients. 231 (62.1%) participants had used CAM for AR in the past 10 years. A higher proportion of females (p = 0.015) and those with higher income (p = 0.004) had used CAM. Among the users, 87.9% found CAM to be effective. No differences were found in terms of age (p = 0.888) and education level (p = 0.057) for CAM usage.

CONCLUSION

CAM is widely used in Malaysia to alleviate AR symptoms, with a large proportion of users think it is effective. Therefore, more researches should be conducted to provide evidence and guidance to integrate CAM into AR management.

An integrative review on the uses of plant-derived bioactives formulated in conventional and innovative dosage forms for the local treatment of damaged nasal cavity

Plants and their derivates have been used as medicines for centuries and today is being re-discovered their usefulness for the human health. The therapeutic properties of phytochemicals are re-evaluated under the light of medical and pharmacological research, pushed by a constantly growing market demand, where consumers trust more natural products than synthetic drugs. New studies are enlightening the effectiveness of phytochemicals against a wide range of ailments, nevertheless very few evaluate the efficacy of topical formulations based on natural bioactive molecules in the treatment of nasal mucosal diseases. This review aims at exploring this little covered topic. An overview on the properties and functionality of the nasal mucosa and the different diseases affecting it has been provided. We summarized various nasal dosage forms containing natural bioactive and explored how innovative delivery systems loading phytochemicals can improve the treatment results. Finally, the potential use of novel nanocarriers for the treatment of nasal ailments has been covered as well.

Middle turbinate resection is unlikely to cause empty nose syndrome in first year postoperatively

PURPOSE

Empty nose syndrome (ENS) is characterized by nasal dryness, crusting, and paradoxical nasal obstruction most commonly after inferior turbinate resection. ENS has also been reported to occur after middle turbinate resection (MTR), and concern for causing ENS is a possible reason surgeons preserve the MT during endoscopic sinus surgery (ESS). The objective was to determine whether MTR during ESS led to ENS.

MATERIALS AND METHODS

This was a prospective case series of 95 consecutive patients that underwent bilateral subtotal MTR during ESS with either Draf IIB or Draf III frontal sinusotomies, for chronic rhinosinusitis with or without nasal polyps, and frontal sinus inverted papillomas. Demographic data and postoperative Empty Nose Syndrome 6-item Questionnaire (ENS6Q) scores were obtained. Nasal crusting was also documented on last postoperative nasal endoscopy.

RESULTS

Pathologies included chronic rhinosinusitis with nasal polyps (69), without nasal polyps (12), and inverted papillomas (14). Fifty-six patients underwent subtotal MTRs during ESS with Draf IIB, and 39 with Draf III. Mean follow-up was 19.4 months (range 12-49). Mean postoperative ENS6Q score was 2.1. Only 2.1% had ENS6Q scores ≥ 11, and 6.3% had nasal crusting at last follow-up. None of the patients with ENS6Q scores ≥ 11 had nasal crusting at last follow-up. There were no significant differences in outcomes between ages, genders, surgery types, or pathologies.

CONCLUSIONS

Patients who underwent bilateral subtotal MTR during ESS were unlikely to develop ENS by at least 1 year postoperatively, based on patients rarely experiencing ENS6Q scores ≥ 11 or persistent nasal crusting.

Trigeminal impairment in treatment-refractory chronic nasal obstruction

BACKGROUND

Patients with anatomically unexplained, chronic nasal obstruction (CNO) that is refractory to medical treatment pose a challenge for clinicians. A surgical solution, addressing mechanical obstacles, is unsuited for these patients. CNO may result from disrupted airflow perception due to activation of the intranasal trigeminal system; therefore, aim of this study is to evaluate if intranasal trigeminal function of these CNO patients is decreased.

METHODS

In this retrospective cross-sectional study, we compared 143 CNO patients and 58 healthy volunteers, between 18 to 80 years old. We assessed nasal patency by means of rhinomanometry (RM) and measured susceptibility of intranasal trigeminal system by the trigeminal lateralization task (TLT).

RESULTS

TLT scores were significantly lower in CNO patients compared to controls (p less than 0.001), but RM scores were not different between groups. Accordingly, TLT allowed to identify CNO patients with an accuracy of the area under the curve (AUC) of 0.78, while the value for RM was at chance (AUC=0.47). CNO patients showed normal reaction to vasoconstrictive agents with significantly lower RM values after Xylomethazoline application.

CONCLUSION

Results suggest that reported nasal obstruction in CNO patients without any obvious anatomical obstacle and resistant to medical treatment may be linked to decreased perception of nasal airflow rather than physical obstruction. In this sub-set of CNO patients, trigeminal testing more adequately reflects the reported obstruction than nasal resistance assessment does. In future studies, the relation of the trigeminal status and the subjective sensation of nasal obstruction needs to be addressed with validated patient rated outcome measures (PROMs).

Appropriate use of essential oils and their components in the management of upper respiratory tract symptoms in patients with COVID-19

Introduction

The involvement of the upper respiratory tract is common in COVID-19, and the majority of patients are treated at home with a mild-to-moderate form of the disease. Many approaches based on essential oils have been proposed for the symptomatic treatment of COVID-19. This work aims to outline the potential and safe evidence-based uses of essential oils and their major components for the clinical management of mild respiratory symptoms caused by uncomplicated coronavirus infections, including SARS-CoV-2. Due to their wide use, a focus on the constituents eucalyptol and menthol has been provided.

Methods

An overview of the scientific literature with a critical discussion of retrieved evidence and clinical recommendations.

Results

In general, eucalyptol and essential oils or blends whose content is rich in it, may be used as an integrative remedy for the symptomatic improvement of patients with mild and uncomplicated infections caused by coronaviruses. Menthol is not recommended in patients with COVID-19, due to a potential reduction of the self-perception of dyspnea, which can lead infected patients to underestimate the actual disease severity and to delay medical attention.

Discussion

Based on available evidence, symptomatic remedies for COVID-19, such as essential oils and their isolated compounds, can be useful, but are not an alternative to standard medical therapy and do not exempt patients from following precautionary measures issued by health authorities. Clinical recommendations on the appropriate use of essential oils for the management of upper airway symptoms of COVID-19 are provided. Further studies on the topic are advised.

COVID-19 and therapy with essential oils having antiviral, anti-inflammatory, and immunomodulatory properties

Coronavirus disease of 2019 (COVID-19) has emerged as a global health threat. Unfortunately, there are very limited approved drugs available with established efficacy against the SARs-CoV-2 virus and its inflammatory complications. Vaccine development is actively being researched, but it may take over a year to become available to general public. Certain medications, for example, dexamethasone, antimalarials (chloroquine/hydroxychloroquine), antiviral (remdesivir), and IL-6 receptor blocking monoclonal antibodies (tocilizumab), are used in various combinations as off-label medications to treat COVID-19. Essential oils (EOs) have long been known to have anti-inflammatory, immunomodulatory, bronchodilatory, and antiviral properties and are being proposed to have activity against SARC-CoV-2 virus. Owing to their lipophilic nature, EOs are advocated to penetrate viral membranes easily leading to membrane disruption. Moreover, EOs contain multiple active phytochemicals that can act synergistically on multiple stages of viral replication and also induce positive effects on host respiratory system including bronchodilation and mucus lysis. At present, only computer-aided docking and few in vitro studies are available which show anti-SARC-CoV-2 activities of EOs. In this review, role of EOs in the prevention and treatment of COVID-19 is discussed. A discussion on possible side effects associated with EOs as well as anti-corona virus claims made by EOs manufacturers are also highlighted. Based on the current knowledge a chemo-herbal (EOs) combination of the drugs could be a more feasible and effective approach to combat this viral pandemic.

Can taste be ergogenic?

Taste is a homeostatic function that conveys valuable information, such as energy density, readiness to eat, or toxicity of foodstuffs. Taste is not limited to the oral cavity but affects multiple physiological systems. In this review, we outline the ergogenic potential of substances that impart bitter, sweet, hot and cold tastes administered prior to and during exercise performance and whether the ergogenic benefits of taste are attributable to the placebo effect. Carbohydrate mouth rinsing seemingly improves endurance performance, along with a potentially ergogenic effect of oral exposure to both bitter tastants and caffeine although subsequent ingestion of bitter mouth rinses is likely required to enhance performance. Hot and cold tastes may prove beneficial in circumstances where athletes' thermal state may be challenged. Efficacy is not limited to taste, but extends to the stimulation of targeted receptors in the oral cavity and throughout the digestive tract, relaying signals pertaining to energy availability and temperature to appropriate neural centres. Dose, frequency and timing of tastant application likely require personalisation to be most effective, and can be enhanced or confounded by factors that relate to the placebo effect, highlighting taste as a critical factor in designing and administering applied sports science interventions.

Enhanced Decision Making and Working Memory During Exercise in the Heat With Crushed Ice Ingestion

PURPOSE

To examine the effects of precooling via crushed ice ingestion on cognitive function during exercise in the heat.

METHODS

Eleven active men ingested either 7 g·kg-1 of crushed ice (ICE) or thermoneutral water (CON) 30 minutes before running 90 minutes on a treadmill at a velocity equivalent to 65% VO2peak in hot and humid conditions (35.0°C [0.5°C], 53.1% [3.9%] relative humidity). Participants completed 3 cognitive tasks to investigate decision making (8-choice reaction time [CRT]), working memory (serial seven [S7]), and executive control (color multisource interference task [cMSIT]) on arrival, after precooling, and after running.

RESULTS

Precooling significantly decreased preexercise core (Tcore) and forehead skin temperature in ICE compared with CON, respectively (Tcore 0.8°C [0.4°C], -0.2°C [0.1°C]; Thead -0.5°C [0.4°C], 0.2°C [0.8°C]; P ≤ .05). Postrun, ICE significantly reduced errors compared with CON for CRT (P ≤ .05; d = 0.90; 90% confidence interval, 0.13-1.60) and S7 (P ≤ .05; d = 1.05; 90% confidence interval, 0.26-1.75). Thermal sensation was lower after precooling with ICE (P ≤ .05), but no significant differences were recorded between conditions for cMSIT errors, skin temperature, heart rate, or ratings of perceived exertion or perceived thirst (P > .05).

CONCLUSIONS

Precooling via ICE maintained cognitive accuracy in decision making and working memory during exercise in the heat. Thus, ICE may have the potential to improve sporting performance by resisting deleterious effects of exercise in a hot and humid environment on cognitive function.

Menthol-induced facilitation of cerebrocortical excitatory propagation induced by air puff stimulation of the nasal cavity in the rat: An optical imaging study

Temperature plays a critical role in the sensation of airflow in the nasal mucosa. Neural activities of the ethmoidal nerve, a trigeminal afferent, responding to airflow are suppressed by warm airflow, whereas cold airflow enhances the ethmoidal nerve activities, which is mimicked by application of menthol, a cold-sensitive TRPM8 receptor agonist. However, it has been an open issue how menthol modulates the spatiotemporal profiles of neural activities of somatosensory cortical neurons. In this study, we assessed neural responses to an air puff stimulation (100 ms) to the nasal cavity in the absence or presence of l-menthol using an optical imaging technique with a voltage-sensitive dye in the primary cortex (S1) of urethane-anesthetized rats. A weak air puff application (15 psi) without l-menthol induced neural excitation in a part of the contralateral S1. The air puff stimulation with l-menthol significantly increased the optical signal intensity, expanded the activated area, and shortened the latency, compared to those in the absence of l-menthol. These results suggest that activation of cold-sensitive TRPM8 receptors sharpens airflow sensation in the nasal cavity and expands the receptive field, especially toward the pharynx, which may contribute to enhanced flavor perception.

Drugs Affecting TRP Channels

Chronic obstructive pulmonary disease (COPD) and asthma are both common respiratory diseases that are associated with airflow reduction/obstruction and pulmonary inflammation. Whilst drug therapies offer adequate symptom control for many mild to moderate asthmatic patients, severe asthmatics and COPD patients symptoms are often not controlled, and in these cases, irreversible structural damage occurs with disease progression over time. Transient receptor potential (TRP) channels, in particular TRPV1, TRPA1, TRPV4 and TRPM8, have been implicated with roles in the regulation of inflammation and autonomic nervous control of the lungs. Evidence suggests that inflammation elevates levels of activators and sensitisers of TRP channels and additionally that TRP channel expression may be increased, resulting in excessive channel activation. The enhanced activity of these channels is thought to then play a key role in the propagation and maintenance of the inflammatory disease state and neuronal symptoms such as bronchoconstriction and cough. For TRPM8 the evidence is less clear, but as with TRPV1, TRPA1 and TRPV4, antagonists are being developed by multiple companies for indications including asthma and COPD, which will help in elucidating their role in respiratory disease.

TRPV1 and TRPM8 in Treatment of Chronic Cough

Chronic cough is common in the population, and among some there is no evident medical explanation for the symptoms. Such a refractory or idiopathic cough is now often regarded as a neuropathic disease due to dysfunctional airway ion channels, though the knowledge in this field is still limited. Persistent coughing and a cough reflex easily triggered by irritating stimuli, often in combination with perceived dyspnea, are characteristics of this disease. The patients have impaired quality of life and often reduced work capacity, followed by social and economic consequences. Despite the large number of individuals suffering from such a persisting cough, there is an unmet clinical need for effective cough medicines. The cough treatment available today often has little or no effect. Adverse effects mostly follow centrally acting cough drugs comprised of morphine and codeine, which demands the physician's awareness. The possibilities of modulating airway transient receptor potential (TRP) ion channels may indicate new ways to treat the persistent cough "without a reason". The TRP ion channel vanilloid 1 (TRPV1) and the TRP melastin 8 (TRPM8) appear as two candidates in the search for cough therapy, both as single targets and in reciprocal interaction.

Menthol tobacco use is correlated with mental health symptoms in a national sample of young adults: implications for future health risks and policy recommendations

Background

Depression and anxiety are correlated with greater nicotine dependence, smoking persistence, and relapse back to smoking after a quit attempt. Menthol cigarette smoking, which is prevalent in young adults, is associated with nicotine dependence, progression to regular smoking, and worse cessation outcomes than non-menthol smoking. Few have established a link between menthol tobacco use, beyond just smoking, with mental health in this high-risk age group. This study examined the association of menthol tobacco use to anxiety and depression in a national sample of young adults.

Methods

Data were from Waves 1 through 7 (n = 9720, weighted) of the Truth Initiative Young Adult Cohort, a national sample of men and women aged 18 to 34 assessed every 6-months. Demographics, past 30-day use of non-menthol and menthol tobacco products, and current alcohol, marijuana, and other drug use were assessed among those with depression and anxiety.

Results

Thirty nine percent of current tobacco users used menthol as their preferred brand. Using a cross-sectional analysis (collapsed across waves), past 30-day menthol tobacco was uniquely associated with greater odds of both depression and anxiety, beyond the effects of demographic and substance correlates and non-menthol tobacco product use.

Conclusions

Menthol is disproportionately used among young adults tobacco users with mental health problems, above and beyond the impact of a variety of other mental health and tobacco use risk factors. Findings suggest a strong link between menthol tobacco use and poor health outcomes. Policies should be developed to deter menthol tobacco use in vulnerable groups.

The physiological mechanism for sensing nasal airflow: a literature review

BACKGROUND

Nasal obstruction is a common otolaryngologic complaint, yet the mechanism of sensing airflow is not commonly understood. The objective of this work was to review current knowledge on the physiological mechanism for sensing nasal airflow.

METHODS

Current literature pertaining to nasal sensation to airflow was retrieved using PubMed and Google Scholar searches.

RESULTS

The primary physiological mechanism that produces the sensation of ample nasal airflow is activation of trigeminal cool thermoreceptors, specifically transient receptor potential melastatin family member 8 (TRPM8), by nasal mucosal cooling. The dynamic change in temperature is ultimately sensed. Nasal mucosal cooling is a result of conductive heat loss, driven by temperature gradient, and evaporative heat loss, driven by humidity gradient. The perception of ample nasal airflow is dependent on the overall nasal surface area stimulated by mucosal cooling, which is mainly governed by air flow patterns. Cool thermoreceptors in the nasal mucosa are connected to the respiratory centers and consequently can alter respiration patterns. Mechanoreceptors do not seem to play a role in sensing nasal airflow. Computational fluid dynamics (CFD) modeling could be a valuable objective tool in evaluating patients with nasal congestion.

CONCLUSION

Understanding the physiological mechanism of how the nose senses airflow can aid in diagnosing the cause behind patient symptoms, which allows physicians to provide better treatment options for patients.

Effects of caffeine and menthol on cognition and mood during simulated firefighting in the heat

This study examined the separate effects of caffeine and menthol on cognition and mood during simulated firefighting in the heat. Participants (N = 10) performed three trials in a counterbalanced order, either with 400 mg caffeine, menthol lozenges, or placebo. The simulated firefighting consisted of 2 bouts of 20-min treadmill exercise and one bout of 20-min stepping exercise in the heat with two brief 15-min rest periods between each exercise phase. Exercise induced significant dehydration (>3%) and elevated rectal temperature (>38.9 °C), for all three conditions. Neither caffeine nor menthol reduced perceived exertion compared to placebo (p > 0.05). Mood ratings (i.e., alertness, hedonic tone, tension) significantly deteriorated over time (p < 0.05), but there was no difference among the three conditions. Simple reaction time, short-term memory, and retrieval memory did not alter with treatments or repeated evaluations. Reaction accuracy from a math test remained unchanged throughout the experimental period; reaction time from the math test was significantly faster after exposure to the heat (p < 0.05). It is concluded that, exhaustive exercise in the heat severely impacted mood, but minimally impacted cognition. These treatments failed to show ergogenic benefits in a simulated firefighting paradigm in a hot environment.

Transient receptor potential (TRP) channels in the airway: role in airway disease

Over the last few decades, there has been an explosion of scientific publications reporting the many and varied roles of transient receptor potential (TRP) ion channels in physiological and pathological systems throughout the body. The aim of this review is to summarize the existing literature on the role of TRP channels in the lungs and discuss what is known about their function under normal and diseased conditions. The review will focus mainly on the pathogenesis and symptoms of asthma and chronic obstructive pulmonary disease and the role of four members of the TRP family: TRPA1, TRPV1, TRPV4 and TRPM8. We hope that the article will help the reader understand the role of TRP channels in the normal airway and how their function may be changed in the context of respiratory disease.

TRP modulation by natural compounds

The use of medicinal plants or other naturally derived products to relieve illness can be traced back over several millennia, and these natural products are still extensively used nowadays. Studies on natural products have, over the years, enormously contributed to the development of therapeutic drugs used in modern medicine. By means of the use of these substances as selective agonists, antagonists, enzyme inhibitors or activators, it has been possible to understand the complex function of many relevant targets. For instance, in an attempt to understand how pepper species evoke hot and painful actions, the pungent and active constituent capsaicin (from Capsicum sp.) was isolated in 1846 and the receptor for the biological actions of capsaicin was cloned in 1997, which is now known as TRPV1 (transient receptor potential vanilloid 1). Thus, TRPV1 agonists and antagonists have currently been tested in order to find new drug classes to treat different disorders. Indeed, the transient receptor potential (TRP) proteins are targets for several natural compounds, and antagonists of TRPs have been synthesised based on the knowledge of naturally derived products. In this context, this chapter focuses on naturally derived compounds (from plants and animals) that are reported to be able to modulate TRP channels. To clarify and make the understanding of the modulatory effects of natural compounds on TRPs easier, this chapter is divided into groups according to TRP subfamilies: TRPV (TRP vanilloid), TRPA (TRP ankyrin), TRPM (TRP melastatin), TRPC (TRP canonical) and TRPP (TRP polycystin). A general overview on the naturally derived compounds that modulate TRPs is depicted in Table 1.

The effect of inhaled menthol on upper airway resistance in humans: a randomized controlled crossover study

BACKGROUND

Menthol (l-menthol) is a naturally-occurring cold receptor agonist commonly used to provide symptomatic relief for upper airway congestion. Menthol can also reduce the sensation of dyspnea. It is unclear whether the physiological action of menthol in dyspnea reduction is through its cold receptor agonist effect or whether associated mechanical changes occur in the upper airway.

OBJECTIVE

To determine whether menthol inhalation alters upper airway resistance in humans.

METHODS

A randomized, sham-controlled, single-blinded crossover study of inhaled menthol on upper airway resistance during semirecumbent quiet breathing in healthy subjects was conducted. Ten healthy participants (eight female) with a mean (± SD) age of 21±1.6 years completed the study.

RESULTS

Nasal resistance before testing was similar on both occasions. No differences were found in respiratory frequency (mean ± SEM) (menthol 17.0±1.1 cmH2O⁄L⁄s; sham 16.9±0.9 cmH2O⁄L⁄s), minute ventilation (menthol 7.7±0.5 cmH2O⁄L⁄s; sham 7.9±0.5 cmH2O⁄L⁄s) or total inspiratory time⁄total breath time (menthol 0.4±0.1 cmH2O⁄L⁄s; sham 0.4±0.1 cmH2O⁄L⁄s). The upper airway resistance was similar during menthol (3.47±0.32 cmH2O⁄L⁄s) and sham (3.27±0.28 cmH2O⁄L⁄s) (P=0.33) inhalation.

CONCLUSION

Inhalation of menthol does not alter upper airway resistance in awake human subjects.

Acoustic rhinometry, rhinomanometry and visual analogue scale before and after septal surgery: a prospective 10-year follow-up

OBJECTIVES

The aim of the study was to compare rhinomanometry, acoustic rhinometry and subjective estimation of the nasal obstruction before and after septoplasty and to evaluate the long-term results of septal surgery.

DESIGN

Prospective long-term follow-up, before and after septoplasty.

SETTING

University tertiary-care hospital, referral centre.

PARTICIPANTS

The study included 30 adult patients who were operated on because of septal deviation.

MAIN OUTCOME MEASURES

Pre-operatively, acoustic rhinometry and active anterior rhinomanometry were performed on each subject after decongestion of the nose. A visual analogue scale for unilateral nasal obstruction was filled in by the patients. The measurements were repeated both 6 months and 10 years post-operatively.

RESULTS

A significant change in acoustic values was found during the long-term follow-up of 10 years. The mean minimal cross-sectional area on the more obstructive side was 0.35 cm(2) pre-operatively. Six months after operation, it was 0.52 cm(2), and 10 years after operation, it was 0.68 cm(2). The mean resistance fell from pre-operative 1.16 Pa/mL/s to 0.41 Pa/mL/s during the first 6 months, but rose again to 1.21 Pa/mL/s after 10 years. Despite a tendency of improvement, no statistically significant change was found between pre-operative and postoperative values in VAS. Six months after operation 69% of the patients were satisfied with the result, and after ten years the amount of satisfied patients was 83%.

CONCLUSIONS

We found an increase in acoustic values, but an increase in nasal resistance in the long-term follow-up. Other factors than nasal area may have an impact on nasal resistance and the feeling of nasal obstruction. The small size on the sample interfered with the results.

The role of trigeminal nasal TRPM8-expressing afferent neurons in the antitussive effects of menthol

The cold-sensitive cation channel TRPM8 is a target for menthol, which is used routinely as a cough suppressant and as an additive to tobacco and food products. Given that cold temperatures and menthol activate neurons through gating of TRPM8, it is unclear how menthol actively suppresses cough. In this study we describe the antitussive effects of (-)-menthol in conscious and anesthetized guinea pigs. In anesthetized guinea pigs, cough evoked by citric acid applied topically to the tracheal mucosa was suppressed by menthol only when it was selectively administered as vapors to the upper airways. Menthol applied topically to the tracheal mucosa prior to and during citric acid application or administered continuously as vapors or as an aerosol to the lower airways was without effect on cough. These actions of upper airway menthol treatment were mimicked by cold air delivered to the upper airways but not by (+)-menthol, the inactive isomer of menthol, or by the TRPM8/TRPA1 agonist icilin administered directly to the trachea. Subsequent molecular analyses confirmed the expression of TRPM8 in a subset of nasal trigeminal afferent neurons that do not coincidently express TRPA1 or TRPV1. We conclude that menthol suppresses cough evoked in the lower airways primarily through a reflex initiated from the nose.

Effects of chewing menthol gum on the alertness of healthy volunteers and those with an upper respiratory tract illness

Recent research has shown that chewing gum increases subjective alertness. Upper respiratory tract illnesses (URTIs) lead to reduced alertness, and it has been shown that stimulants such as caffeine can reverse this effect. It is now important to determine whether menthol chewing gum can produce a similar effect. Young adults with an URTI (N = 16) and a healthy control group (N = 12) rated their mood and symptoms on two occasions (the first when those with a URTI were ill and the second when both groups were healthy). During each session, volunteers provided a rating while chewing gum and when they were not chewing. Those with a URTI reported reduced alertness, which persisted into convalescence. Chewing gum was associated with greater alertness in both those with URTIs and the healthy group. Chewing gum reduced the severity of nasal symptoms in those with a cold. The effects of the URTI and menthol gum may reflect changes in trigeminal stimulation.

Inhalation of menthol reduces capsaicin cough sensitivity and influences inspiratory flows in chronic cough

INTRODUCTION

Chronic cough is a common clinical problem and there is a shortage of effective treatments for it. Within the group of transient receptor potential ion channels a receptor for the cooling substance menthol has been identified. This study aimed to assess whether pre-inhalation of dissolved, nebulised menthol could increase capsaicin cough thresholds and influence spirometric values.

METHODS

Fourteen patients with chronic cough and airway sensitivity to environmental irritants and 15 control subjects were tested on three occasions. Each one inhaled a 1 mL of nebulised menthol solution of 0.5% or 1% or placebo (saline with 0.05% menthol) at each visit in a randomized and double-blind order. They were then provoked by capsaicin inhalation.

RESULTS

Patients' cough thresholds differed significantly from the controls' on all three provocations (P < 0.0001). After inhalation of 1% menthol, the patients' cough thresholds were significantly higher (P < 0.02) compared to after placebo inhalation and to after 0.5% menthol inhalation (P < 0.05). The patients' peak inspiratory flows were significantly reduced after inhalation of the placebo (saline) (P < 0.05) but not after inhalation of 0.5% or 1% menthol. Forced inspiratory flows 50% were lowered after inhalation of placebo and of 0.5% menthol (P < 0.05) but not after 1% menthol. Among the controls, forced inspiratory flows 50% were lowered after only placebo inhalation (P < 0.05).

CONCLUSIONS

In patients with chronic cough, pre-inhalation of menthol reduces cough sensitivity to inhaled capsaicin and influences inspiratory flows. The findings may provide scientific support for the common practice of using menthol as a reliever for variant airway discomfort. The use of menthol in different cigarette brands could be questioned since it could conceal the natural irritation following smoking.

Modulation of cough response by sensory inputs from the nose - role of trigeminal TRPA1 versus TRPM8 channels

Background

Cough, the most important airways defensive mechanism is modulated by many afferent inputs either from respiratory tussigenic areas, but also by afferent drive from other organs. In animal models, modulation of cough by nasal afferent inputs can either facilitate or inhibit the cough response, depending on the type of trigeminal afferents stimulated.

Methods

In this study we addressed the question of possible bidirectional modulation of cough response in human healthy volunteers by nasal challenges with TRPA1 and TRPM8 agonists respectively. After nasal challenges with isocyanate (AITC), cinnamaldehyde, (−) menthol and (+) menthol (all 10^-3 M) nasal symptom score, cough threshold (C2), urge to cough (Cu) and cumulative cough response were measured).

Results

Nasal challenges with TRPA1 relevant agonists induced considerable nasal symptoms, significantly enhanced urge to cough (p<0.05) but no statistically significant modulation of the C2 and cumulative cough response. In contrast, both TRPM8 agonists administered to the nose significantly modulated all parameters including C2 (p<0.05), Cu (p<0.01) and cumulative cough response (p <0.01) documenting strong anti irritating potential of menthol isomers.

Conclusions

In addition to trigeminal afferents expressing TRP channels, olfactory nerve endings, trigemino – olfactoric relationships, the smell perception process and other supramedullar influences should be considered as potential modulators of the cough response in humans.

TRP channels as therapeutic targets in airway disorders: a patent review

INTRODUCTION

Chronic respiratory diseases, such as asthma and chronic obstructive pulmonary disease, affect millions of patients worldwide. New therapeutic approaches to these conditions are urgently needed since current treatment options provide only symptomatic relief. Transient receptor potential (TRP) ion channels are emerging molecular target candidates for the development of novel, disease-modifying drugs addressing airway diseases.

AREAS COVERED

The authors review the patent literature on novel molecules targeting TRP channels (in particular TRPA1, TRPV1, TRPM8 and TRPC6) that are currently studied in clinical trials or are candidates for future clinical evaluation in the management of respiratory diseases.

EXPERT OPINION

The patent literature highlights TRPA1 and TRPV1 channels as the most advanced therapeutic targets in respiratory disorders. TRPV1 antagonists relieve cough in preclinical studies. TRPA1 antagonists not only are anti-tussive but also show efficacy in allergic asthma models. However, to date, only minimal clinical data are available regarding the effects of selective, small-molecule TRPV1 and TRPA1 blockers in respiratory disorders. Clearly, long-term clinical studies are required to confirm the expectations based on preclinical data. In conclusion, the current status of this rapidly expanding research area raises cautious optimism for TRPA1 (and possibly also TRPV1) antagonists as promising anti-tussive/anti-asthma drug candidates.

Use of rhinomanometry in common rhinologic disorders

Rhinomanometry is a functional test of nasal aerodynamics that measures transnasal airflow and the pressure gradient allowing nasal resistance to be calculated from these data. Three methods of rhinomanometry that are currently in use are anterior rhinomanometry, posterior (peroral) rhinomanometry and postnasal (pernasal) rhinomanometry. The usefulness of this method has increased owing to the development of technology and use of microcomputers connected to the measuring devices. Rhinomanometry can be used for: clinical evaluation of the symptom of nasal obstruction; research in nasal physiology; allergy challenge testing; pre- and post-treatment assessments of surgical or medical therapy; and evaluation of patients with sleep apnea.

Empty nose syndrome: limbic system activation observed by functional magnetic resonance imaging

OBJECTIVES/HYPOTHESIS

Empty nose syndrome (ENS) patients have a persistent sense of impaired nasal patency despite radical resection of nasal turbinates. The aim of this study was to elucidate differences in cerebral activation during free breathing and after inhalation of a fragrance (lemonene) and a pseudodecongestant (menthol) over a nasofacial mask. Our hypothesis was that menthol would be perceived as beneficial and that cerebral activation would show differences in areas corresponding to emotional suffering and air hunger in ENS patients.

STUDY DESIGN

Prospective, controlled intervention with lemonene and menthol during functional magnetic resonance imaging (f-MRI) experiment.

METHODS

Ten right-handed ENS patients were compared to 15 controls using f-MRI and fully automated data analysis with SPM software. Nasal patency was measured with rhinomanometry and rated on a four-point scale.

RESULTS

Despite similar objective nasal flow, ENS patients rated nasal patency significantly worse than did controls. Menthol was perceived to increase nasal patency. In patients, f-MRI data showed different activation of temporal cortex areas after inhalation of menthol. The comparison of patients and controls showed ENS-specific activation of temporal and cerebellar areas and amygdala during the rating task itself.

CONCLUSIONS

Our experiments showed different cerebral processing of the feeling of nasal patency in ENS patients with prominent activation of areas belonging to the limbic system. The beneficial effect of menthol seems to correspond to activation differences in the temporal pole. These results demonstrate a neuronal substrate for both symptoms and their relief in ENS patients.

TRPM8 and dyspnea: from the frigid and fascinating past to the cool future?

The transient receptor potential melastatin 8 (TRPM8) ion channel is gated by cool and noxious cold temperatures. The activation threshold is in the range of ≈25-28°C, which aligns well with the discharge of airway afferents. TRPM8 is widely expressed across species and evolutionary changes in the TRPM8 amino acid sequence may tune the temperatures at which it is gated. The discovery of TRPM8 and its molecular/biophysical characterization provides a robust candidate for airway afferents responding to cool/cold temperatures. TRPM8 may provide a mechanistic link for the manipulation of respiratory sensations such as dyspnea or mechanisms leading to cold-induced asthma and cough.

The impact of menthol cigarettes on smoking initiation among non-smoking young females in Japan

Japan presents an excellent case-study of a nation with low female smoking rates and a negligible menthol market which changed after the cigarette market was opened to foreign competition. Internal tobacco industry documents demonstrate the intent of tobacco manufacturers to increase initiation among young females through development and marketing of menthol brands. Japanese menthol market share rose rapidly from less than 1% in 1980 to 20% in 2008. Menthol brand use was dominated by younger and female smokers, in contrast with non-menthol brands which were used primarily by male smokers. Nationally representative surveys confirm industry surveys of brand use and provide further evidence of the end results of the tobacco industry’s actions—increased female smoking in Japan. These findings suggest that female populations may be encouraged to initiate into smoking, particularly in developing nations or where female smoking rates remain low, if the tobacco industry can successfully tailor brands to them. The Japanese experience provides a warning to public health officials who wish to prevent smoking initiation among young females.

Pathophysiology of nasal congestion

Nasal congestion is a common symptom in rhinitis (both allergic and nonallergic), rhinosinusitis and nasal polyposis. Congestion can also be caused by physical obstruction of nasal passages and/or modulation of sensory perception. Mucosal inflammation underlies many of the specific and interrelated factors that contribute to nasal congestion, as well as other symptoms of both allergic rhinitis and rhinosinusitis. A wide range of biologically active agents (eg, histamine, tumor necrosis factor-α, interleukins, cell adhesion molecules) and cell types contribute to inflammation, which can manifest as venous engorgement, increased nasal secretions and tissue swelling/edema, ultimately leading to impaired airflow and the sensation of nasal congestion. Inflammation-induced changes in the properties of sensory afferents (eg, expression of peptides and receptors) that innervate the nose can also contribute to altered sensory perception, which may result in a subjective feeling of congestion. Increased understanding of the mechanisms underlying inflammation can facilitate improved treatment selection and the development of new therapies for congestion.

Treatment of congestion in upper respiratory diseases

Congestion, as a symptom of upper respiratory tract diseases including seasonal and perennial allergic rhinitis, acute and chronic rhinosinusitis, and nasal polyposis, is principally caused by mucosal inflammation. Though effective pharmacotherapy options exist, no agent is universally efficacious; therapeutic decisions must account for individual patient preferences. Oral H₁-antihistamines, though effective for the common symptoms of allergic rhinitis, have modest decongestant action, as do leukotriene receptor antagonists. Intranasal antihistamines appear to improve congestion better than oral forms. Topical decongestants reduce congestion associated with allergic rhinitis, but local adverse effects make them unsuitable for long-term use. Oral decongestants show some efficacy against congestion in allergic rhinitis and the common cold, and can be combined with oral antihistamines. Intranasal corticosteroids have broad anti-inflammatory activities, are the most potent long-term pharmacologic treatment of congestion associated with allergic rhinitis, and show some congestion relief in rhinosinusitis and nasal polyposis. Immunotherapy and surgery may be used in some cases refractory to pharmacotherapy. Steps in congestion management include (1) diagnosis of the cause(s), (2) patient education and monitoring, (3) avoidance of environmental triggers where possible, (4) pharmacotherapy, and (5) immunotherapy (for patients with allergic rhinitis) or surgery for patients whose condition is otherwise uncontrolled.

Bepotastine besilate OD tablets suppress nasal symptoms caused by Japanese cedar pollen exposure in an artificial exposure chamber (OHIO Chamber)

OBJECTIVE

To investigate the efficacy and safety of bepotastine, we conducted a randomized, investigator-blind, placebo-controlled and parallel study to evaluate the allergic symptoms and the cognitive function of the subjects with Japanese cedar (JC) pollinosis in response to JC pollen exposure in an artificial exposure chamber.

METHODS

Twenty-four volunteers with JC pollinosis were enrolled in this study. The subjects were randomly divided into two groups: a bepotastine group and a placebo group (12 subjects each). Subjects received either a 10-mg bepotastine OD (orally disintegrating) tablet or a placebo 10 min before entering the chamber for a 3-h exposure. The nasal and ocular symptoms were evaluated by each patient at regular intervals. The amount of nasal discharge was measured and the number of sneezes recorded. To evaluate the cognitive function, a digit cancellation test (D-CAT), in which the subjects have to eliminate certain numbers within a fixed time, was conducted.

RESULTS

Twelve subjects in the placebo group developed nasal and/or ocular symptoms, whereas six subjects in the bepotastine group showed none of the symptoms during exposure. Mean secretion weights and number of sneezes were significantly lower in the bepotastine group than in the placebo group. In D-CAT, no deterioration of work performance was observed in the bepotastine group. No adverse effects were observed in either group.

CONCLUSION

Bepotastine treatment is effective and well tolerated in patients with allergen-induced symptoms exposed to JC pollen in an exposure chamber.

A natural history of botanical therapeutics

Plants have been used as a source of medicine throughout history and continue to serve as the basis for many pharmaceuticals used today. Although the modern pharmaceutical industry was born from botanical medicine, synthetic approaches to drug discovery have become standard. However, this modern approach has led to a decline in new drug development in recent years and a growing market for botanical therapeutics that are currently available as dietary supplements, drugs, or botanical drugs. Most botanical therapeutics are derived from medicinal plants that have been cultivated for increased yields of bioactive components. The phytochemical composition of many plants has changed over time, with domestication of agricultural crops resulting in the enhanced content of some bioactive compounds and diminished content of others. Plants continue to serve as a valuable source of therapeutic compounds because of their vast biosynthetic capacity. A primary advantage of botanicals is their complex composition consisting of collections of related compounds having multiple activities that interact for a greater total activity.

Impact of Menthol Inhalation on Nasal Mucosal Temperature and Nasal Patency

Background

Menthol is a natural herbal compound. Its isomer L-menthol presents the characteristic peppermint scent and is also responsible for the cooling sensation when applied to nasal mucosal surfaces because of stimulation of trigeminal cold receptors. The aim of this study was to assess the effect of menthol inhalation on end-inspiratory nasal mucosa temperature and nasal patency.

Methods

Eighteen healthy volunteers with a mean age of 30 years were enrolled in this study. Objective measurements included the septal mucosal temperature within the nasal valve area by using a miniaturized thermocouple as well as active anterior rhinomanometry before and after inhalation of l-menthol vapor. All subjects completed a visual analog scale (VAS; range, 1–10) evaluating nasal patency before and after menthol.

Results

The mean end-inspiratory mucosal temperature ranged from 27.7°C (±4.0) before menthol inhalation to 28.5°C (±3.5) after menthol inhalation. There were no statistically significant differences between the temperature values before and after menthol inhalation (p > 0.05). In addition, no statistically significant differences between the rhinomanometric values before and after menthol inhalation were observed. Sixteen of the 18 subjects reported an improvement of nasal breathing after menthol inhalation by means of the VAS.

Conclusion

Menthol inhalation does not have an effect on nasal mucosal temperature and nasal airflow. The subjective impression of an improved nasal airflow supports the fact that menthol leads to a direct stimulation of cold receptors modulating the cool sensation, entailing the subjective feeling of a clear and wide nose.