Nasal 'flow' receptors of the rat

Which Nasal Airway Dimensions Correlate with Nasal Airflow and with Nasal Breathing Sensation?

Background: Rhinoplasty modifies the nasal pyramid, thereby also modifying the nasal airway. Objectives: To correlate the sensation of nasal breathing, as measured by patient-reported outcome measures, and nasal airflow, as assessed by peak nasal inspiratory flow (PNIF), with nasal airway dimensions, as measured on computed tomography (CT) images. Methods: Fifty Caucasian patients were studied through visual analogue scale (VAS), nasal obstruction symptom evaluation (NOSE) and PNIF. Measurements of the nasal airway were made on CT images: minimal distance between septum and inferior and middle turbinates, nasal valve angle, and nasal valve area. Results: There was a significant association between PNIF and nasal valve area, between VAS and the narrower nasal valve angle and between NOSE and minimal distance between septum and middle turbinate of the narrower side. Conclusions: This study suggests that the dimensions of the nasal valve and of the middle nasal airway have a substantial impact on nasal breathing capacity. It also highlights the importance of unilateral nasal airway obstruction to nasal breathing.

Algorithm for Nasal Breathing Impairment Evaluation

Assessing patients with complaints of nasal obstruction has traditionally been done by evaluation of the nasal airway looking for fixed or dynamic obstructive locations that could impair nasal airflow. Not infrequently, however, symptoms of nasal obstruction do not match the clinical examination of the nasal airway. Addressing this subset of patients may be a challenge to the surgeon. Evaluation of patients with symptoms of nasal obstruction should include a combination of a patient-reported assessment of nasal breathing and at least one objective method for measuring nasal airflow or nasal airway resistance or dimensions. This will allow distinction between patients with symptoms of nasal obstruction and low airflow or high nasal airway resistance and patients with similar symptoms but whose objective evaluation demonstrates normal nasal airflow or normal airway dimensions or resistance. Patients with low nasal airflow or high nasal airway resistance will require treatment to increase nasal airflow as a necessary step to improve symptoms, whereas patients with normal nasal airflow or nasal airway resistance will require a multidimensional assessment looking for less obvious causes of impaired nasal breathing sensation.

Overview of Nasal Airway and Nasal Breathing Evaluation

Several methods are available for evaluating nasal breathing and nasal airflow, as this evaluation may be made from several different perspectives.Physiologic methods for nasal airway evaluation directly measure nasal airflow or nasal airway resistance, while anatomical methods measure nasal airway dimensions. Subjective methods evaluate nasal breathing through several validated patient-reported scales assessing nasal breathing. Computational fluid dynamics evaluates nasal airflow through the analysis of several physics' variables of the nasal airway.Being familiar to these methods is of utmost importance for the nasal surgeon to be able to understand data provided by the different methods and to be able to choose the combination of evaluation methods that will provide the information most relevant to each clinical situation.

Objective measurement and patient-reported evaluation of the nasal airway: Is correlation dependent on symptoms or on nasal airflow?

BACKGROUND

Evidence has shown that the sensation of nasal breathing is related to variations in nasal mucosa temperature produced by airflow. An appropriate nasal airflow is necessary for changing mucosal temperature. Therefore, the correlation between objective measurements of nasal airflow and patient-reported evaluation of nasal breathing should be dependent on the level of nasal airflow.

OBJECTIVES

To find if the correlation between patient-reported assessment of nasal breathing and objective measurement of nasal airflow is dependent on the severity of symptoms of nasal obstruction or on the level of nasal airflow.

METHODS

The airway of 79 patients was evaluated using NOSE score and peak nasal inspiratory flow (PNIF). Three subgroups were created based on NOSE and three subgroups were created based on PNIF level to find if correlation was dependent on nasal symptoms or airflow.

RESULTS

The mean value of PNIF for the 79 patients was 92.6 L/min (SD 28.1 L/min). The mean NOSE score was 48.4 (SD 24.4). The correlation between PNIF and NOSE was statistically significant (P = .03), but with a weak association between the two variables (r = -.248). Evaluation of correlation based on symptoms demonstrated a weak or very weak association in each subgroup (r = -.250, r = -.007, r = -.104). Evaluation of correlation based on nasal airflow demonstrated a very weak association for the subgroups with middle-level and high PNIF values (r = -.190, r = -.014), but a moderate association for the subgroup with low PNIF values (r = -.404).

CONCLUSIONS

This study demonstrated a weak correlation between NOSE scores and PNIF values in patients non-selected according to symptoms of nasal obstruction or to airflow. It demonstrated that patients with symptoms of nasal obstruction have different levels of nasal airflow and that low nasal airflow prevents the sensation of good nasal breathing. Therefore, patients with symptoms of nasal obstruction may require improving nasal airflow to improve nasal breathing sensation.

An Overview of Computational Fluid Dynamics Preoperative Analysis of the Nasal Airway

Evaluation of the nasal airway is crucial for every patient with symptoms of nasal obstruction as well as for every patient with other nasal symptoms. This assessment of the nasal airway comprises clinical examination together with imaging studies, with the correlation between findings of this evaluation and symptoms reported by the patient being based on the experience of the surgeon. Measuring nasal airway resistance or nasal airflow can provide additional data regarding the nasal airway, but the benefit of these objective measurements is limited due to their lack of correlation with patient-reported evaluation of nasal breathing. Computational fluid dynamics (CFD) has emerged as a valuable tool to assess the nasal airway, as it provides objective measurements that correlate with patient-reported evaluation of nasal breathing. CFD is able to evaluate nasal airflow and measure variables such as heat transfer or nasal wall shear stress, which seem to reflect the activity of the nasal trigeminal sensitive endings that provide sensation of nasal breathing. Furthermore, CFD has the unique capacity of making airway analysis of virtual surgery, predicting airflow changes after trial virtual modifications of the nasal airway. Thereby, CFD can assist the surgeon in deciding surgery and selecting the surgical techniques that better address the features of each specific nose. CFD has thus become a trend in nasal airflow assessment, providing reliable results that have been validated for analyzing airflow in the human nasal cavity. All these features make CFD analysis a mainstay in the armamentarium of the nasal surgeon. CFD analysis may become the gold standard for preoperative assessment of the nasal airway.

Reflexes that impact spontaneous breathing of preterm infants at birth: a narrative review

Some neural circuits within infants are not fully developed at birth, especially in preterm infants. Therefore, it is unclear whether reflexes that affect breathing may or may not be activated during the neonatal stabilisation at birth. Both sensory reflexes (eg, tactile stimulation) and non-invasive ventilation (NIV) can promote spontaneous breathing at birth, but the application of NIV can also compromise breathing by inducing facial reflexes that inhibit spontaneous breathing. Applying an interface could provoke the trigeminocardiac reflex (TCR) by stimulating the trigeminal nerve resulting in apnoea and a reduction in heart rate. Similarly, airflow within the nasopharynx can elicit the TCR and/or laryngeal chemoreflex (LCR), resulting in glottal closure and ineffective ventilation, whereas providing pressure via inflations could stimulate multiple receptors that affect breathing. Stimulating the fast adapting pulmonary receptors may activate Head's paradoxical reflex to stimulate spontaneous breathing. In contrast, stimulating the slow adapting pulmonary receptors or laryngeal receptors could induce the Hering-Breuer inflation reflex or LCR, respectively, and thereby inhibit spontaneous breathing. As clinicians are most often unaware that starting primary care might affect the breathing they intend to support, this narrative review summarises the currently available evidence on (vagally mediated) reflexes that might promote or inhibit spontaneous breathing at birth.

Comparing the effect of two different interfaces on breathing of preterm infants at birth: A matched-pairs analysis

OBJECTIVE

Applying a face mask could provoke a trigeminocardiac reflex. We compared the effect of applying bi-nasal prongs with a face mask on breathing and heart rate of preterm infants at birth.

METHODS

In a retrospective matched-pairs study of infants <32 weeks of gestation, the use of bi-nasal prongs for respiratory support at birth was compared to the use of a face mask. Infants who were initially breathing at birth and subsequently received respiratory support were matched for gestational age (±4 days), birth weight (±300 g), general anaesthesia and gender. Breathing, heart rate and other parameters were collected before and after interface application and in the first 5 min thereafter.

RESULTS

In total, 130 infants were included (n = 65 bi-nasal prongs, n = 65 face mask) with a median (IQR) gestational age of 27⁺² (25⁺³-28⁺⁴) vs 26⁺⁶ (25⁺³-28⁺⁵) weeks. The proportion of infants who stopped breathing after applying the interface was not different between the groups (bi-nasal prongs 43/65 (66%) vs face mask 46/65 (71%), p = 0.70). Positive pressure ventilation was given more often when bi-nasal prongs were used (55/65 (85%) vs 40/65 (62%), p < 0.001). Heart rate (101 (75-145) vs 110 (68-149) bpm, p = 0.496) and oxygen saturation (59% (48-87) vs 56% (35-84), p = 0.178) were similar in the first 5 min after an interface was applied in the infants who stopped breathing.

CONCLUSION

Apnoea and bradycardia occurred often after applying either bi-nasal prongs or a face mask on the face for respiratory support in preterm infants at birth.

Computational fluid dynamic analysis of aggressive turbinate reductions: is it a culprit of empty nose syndrome?

BACKGROUND

Empty nose syndrome (ENS) remains highly controversial, with aggressive inferior turbinate reduction (ITR) or mucociliary dysfunction frequently implicated. However, the appropriate degree of ITR is highly debatable.

METHODS

We applied individual computed tomography (CT)-based computational fluid dynamics (CFD) to 5 patients receiving relatively aggressive ITR but with no ENS symptoms, and compared them to 27 symptomatic ENS patients who all had histories of aggressive ITRs, and 42 healthy controls. Patients' surgical outcomes were confirmed with 22-item Sino-Nasal Outcome Test (SNOT-22) (ITR: 6.40 ± 4.56; ENS: 58.2 ± 15.9; healthy: 13.2 ± 14.9), Nasal Obstruction Symptom Evaluation (NOSE) scores (ITR: 4.00 ± 2.24; ENS: 69.4 ± 17.1; healthy: 11.9 ± 12.9), and Empty Nose Syndrome 6-Item Questionnaire (ENS6Q) (≥11 for ENS).

RESULTS

Both aggressive ITR without ENS symptoms and symptomatic ENS patients had significantly lower nasal resistance (ITR: 0.059 ± 0.020 Pa·s/mL; ENS: 0.052 ± 0.015 Pa·s/mL; healthy: 0.070 ± 0.021 Pa·s/mL) and higher cross-sectional areas surrounding the inferior turbinate (ITR: 0.94 ± 0.21 cm² ; ENS: 1.19 ± 1.05 cm² ; healthy: 0.42 ± 0.22 cm² ) than healthy controls. The lack of significant differences among patient groups indicated similar degrees of surgeries between ITR with and without ENS symptom cohorts. However, symptomatic ENS patients have paradoxical significantly less airflow in the inferior meatus (ITR: 47.7% ± 23.6%; ENS: 25.8% ± 17.6%; healthy: 36.5 ± 15.9%; both p < 0.01), but higher airflow around the middle meatus (ITR: 49.7% ± 22.6%; ENS: 66.5% ± 18.3%; healthy: 49.9% ± 15.1%, p < 0.0001) than aggressive ITR without symptoms and controls. Aggressive ITR patients have increased inferior meatus airflow as expected (p < 0.05). This imbalanced airflow produced less inferior wall-shear-stress distribution among symptomatic ENS patients only (ITR: 42.45% ± 11.4%; ENS: 32.2% ± 12.6%; healthy: 49.7% ± 9.9%). ENS patients (n = 12) also had impaired nasal trigeminal function, as measured by menthol lateralization detection thresholds (ITR: 15.2 ± 1.2; ENS: 10.3 ± 3.9; healthy: 13.8 ± 3.09, both p < 0.0001). Surprisingly, aggressive ITR patients without ENS symptoms have better menthol lateralization detection thresholds (LDTs) than healthy controls.

CONCLUSION

Although turbinate tissue loss is linked with ENS, the degree of ITR that might distinguish postoperative patient satisfaction in their nasal breathing vs development of ENS symptoms is unclear. Our results suggest that a combination of distorted nasal aerodynamics and loss of mucosal sensory function may potentially lead to ENS symptomology.

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.

The Effects of Nasal Flow Stimulation on Central Respiratory Pattern

The purpose of this study was to analyze the functional role of nasal afferents on central respiratory mechanisms. The electromyographic activity of the diaphragm and the neuronal activities of respiratory neurons within the brainstem were recorded during nasal flow stimulation, using decerebrate cats. Flow stimulation delivered to the nose prolonged the respiratory cycle time and decreased the amplitude of diaphragmatic activity. The respiratory cycle time was prolonged due to prolongation of expiratory phase. Cool air flow stimulation was more effective for changing the respiratory pattern than was warm air. All recorded inspiratory neurons of the dorsal respiratory group decreased their firing rate during stimulation, but more than half of expiratory neurons of the ventral respiratory group did not change. These results suggest that nasal afferents which respond to temperature can modulate the central respiratory pattern and have a stronger suppressive effect on the activity of inspiratory neurons than that of expiratory neurons.

Somatotopic Organization and Temporal Characteristics of Cerebrocortical Excitation in Response to Nasal Mucosa Stimulation With and Without an Odor in the Rat: An Optical Imaging Study

Nasal mucosa has roles in warming and humidifying inspired air and is highly sensitive to mechanical stimuli. Moreover, the upper part of the nasal mucosa expresses olfactory receptors processing olfactory information. Although the somatosensory map of the face in the primary (S1) and secondary (S2) somatosensory cortices is clearly documented, the map of the nasal mucosa and the effect of odors on their activities are largely unknown. This study aimed to identify the cortical regions in S1 and their temporal features in response to somatosensory stimulation of the nasal mucosa using an optical imaging technique in urethane-anesthetized rats. An air puff application response to nasal mucosa first occurred in a part of contralateral S1 and subsequently, spread toward the rostrally and ventrally adjacent sites. Upper pharynx stimulation initially activated this rostrally expanded site and the excitatory propagation from the initially activated region toward ventral region likely represented S2. Signal intensity and activated area increased dependent on air pressure. Nasal tip stimulation initially excited S1 region caudally adjacent to that of nasal mucosa. Moreover, the amplitude of S1 excitation was similar between air puff stimulation with and without an odor, amyl acetate. In contrast to contralateral S1, air puff stimulation with the odor showed a faint optical signal increase in the ipsilateral piriform cortex. These results suggest that somatosensory information from the nasal mucosa and skin, and upper pharynx are processed in spatially continuous regions of S1, and interaction between somatosensory and olfactory systems is relatively small in contralateral S1.

Intranasal trigeminal sensitivity: measurements before and after nasal surgery

Nasal surgeries constitute an extensive manipulation of the nasal mucosa and therefore of structures related to trigeminal and olfactory sensitivity. While olfactory changes due to nasal surgery are relatively well investigated, there are only very few studies regarding trigeminal sensitivity. Aim of the present study was to investigate sensory changes after nasal surgery with special regard to the trigeminal sensitivity. In 38 patients prior to and around 12 weeks after nasal surgery the following psychophysical measures were performed: odor identification, odor discrimination, phenyl ethyl alcohol odor threshold, sensitivity to trigeminal stimuli, trigeminal detection thresholds and trigeminal pain thresholds. These results were compared to those of a control group (43 healthy volunteers). Psychophysical olfactory and trigeminal testing showed no major changes in patients after surgery compared to the control group. Independent from the time of measurement higher trigeminal detection thresholds were found in patients compared to healthy subjects, meaning that trigeminal thresholds were already increased before surgery. The present study revealed a decreased trigeminal sensitivity in patients already before surgery. It may be hypothesized that patients also exhibit a decreased sensitivity for nasal airflow, which may also contribute to the patients' impression of impaired nasal breathing.

Mechanophysical stimulations of mucin secretion in cultures of nasal epithelial cells

Nasal epithelial cells secret mucins and are exposed in vivo to airflow-induced mechanophysical stresses, including wall shear stress (WSS), temperature, and humidity. In this work, human nasal epithelial cells cultured under air-liquid interface conditions were subjected to fields of airflow-induced oscillatory WSS at different temperature and humidity conditions. Changes in mucin secretion due to WSS were measured and the role of the cytoskeleton in mucin secretion was explored. Mucin secretion significantly increased in response to WSS in a magnitude-dependent manner with respect to static cultures and independently of the airflow temperature and humidity. In static cultures, mucin secretion decreased at high humidity with or without elevation of the temperature with respect to cultures at a comfortable climate. In cultures exposed to WSS, mucin secretion increased at high temperature with respect to cultures at comfortable climate conditions. The polymerization of actin microfilaments was shown to increase mucin secretion under WSS, whereas the dynamics of microtubule polymerization did not affect secretion. In conclusion, the data in this study show that mucin secretion is sensitive to oscillatory WSS as well as high temperature and humidity conditions.

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.

Expression of Fos protein in brainstem after application of l-menthol to the rat nasal mucosa

There are two functional pathways for the nasotrigeminal reflex: the spinal nucleus of trigeminal nerve (SPV) to the Kölliker-Fuse (KF) nucleus and the nucleus of solitary tract (NTS) to the lateral parabrachial nucleus (PBl). Although stimulation of the nasal mucosa by cool temperature induces respiratory depression, it is still unknown whether these nuclei are activated. In the present study, we examined the expression of Fos protein in rat brainstem neurons after nasal application of l-menthol, which is known to activate cold-sensitive nasal receptors. Application of l-menthol, but not paraffin oil, decreased the respiratory rate from 99.7+/-15.6 to 78.5+/-7.3 min(-1). Furthermore, a significantly higher density of Fos-immunoreactive cells was observed in the SPV and KF in the l-menthol rats than in the controls. In the SPV, the density of Fos-immunoreactive cells was highest at approximately 0.5mm rostral to the obex in both the l-menthol (48.5+/-11.5 cells/section) and paraffin oil (26.0+/-9.6 cells/section) groups. In the KF, the mean density of Fos-immunoreactive cells was highest at approximately 5.0mm rostral to the obex in both groups (l-menthol: 67.8+/-14.0 cells/section, control: 41.0+/-12.7 cells/section). The present study suggests that the SPV-KF pathway is important for the cold-induced respiratory depression.

Effects of Nasal Surgery on Sleep Quality in Obstructive Sleep Apnea Syndrome with Nasal Obstruction

Background

The purpose of this study was to evaluate the effects of nasal surgery on nasal resistance, sleep apnea, and sleep quality in adult male patients with obstructive sleep apnea syndrome (OSAS). A prospective study was performed in OSAS patients who underwent isolated nasal surgery in a tertiary referral center.

Methods

During the 3-year study period, 49 OSAS patients suffering from symptomatic nasal obstruction/impaired nasal breathing underwent the standard polysomnography before and after surgery. Polysomnography along with measures of nasal resistance and daytime sleepiness (the Epworth sleepiness scale [ESS] scores) were reviewed also.

Results

Surgery decreased the nasal resistance (0.55 ± 0.37 Pa/cm3 per second versus 0.17 ± 0.19 Pa/cm3 per second; p < 0.001) and ESS scores (11.7 ± 4.1 versus 3.3 ± 1.3; p < 0.001), without changes in the apnea-hypopnea index (AHI; 44.6 ± 22.5 versus 42.5 ± 22.0). Surgery increased nadir oxygen saturation (76.2 ± 10.9% versus 78.8 ± 8.1%; p < 0.01), shortened apnea–hypopnea duration (averaged/maximum; 33.5 ± 7.3/61.1 ± 46.0 versus 28.8 ± 7.4/47.3 ± 36.1 second; p < 0.05/p < 0.01), and improved sleep quality.

Conclusion

The results suggest that nasal surgery is useful for lowering nasal resistance, ameliorating sleep-disordered breathing, and improving sleep quality and daytime sleepiness in OSAS.

Nasal mucosal temperature in relation to nasal airflow as measured by rhinomanometry

BACKGROUND

The aim of this study was to measure in vivo nasal mucosal temperature and assess its relationship to nasal patency.

METHODS

Nasal mucosal temperature of 30 nasal cavities was measured by means of a miniaturized thermocouple within the anterior turbinate area during respiration. Temperature values were compared with corresponding rhinomanometrical data.

RESULTS

The median mucosal temperature ranged from 30.2 degrees C (range, 28.9-31.7 degrees C) after inspiration to 32.2 degrees C (range, 31.0-33.9 degrees C) after expiration. The end-inspiratory (r = -0.85) and end-expiratory mucosal temperature values (r = -0.88) negatively correlated with the rhinomanometrical data.

CONCLUSION

This study supports the fact that there is a negative correlation between nasal mucosal temperature and nasal resistance. Changes in nasal patency seem to influence nasal mucosal temperature. Within this context, nasal thermoreceptors might play an important role concerning the perception of nasal patency.

Fos expression in the brainstem nuclei evoked by nasal air-jet stimulation in rats

BACKGROUND

Noxious stimulation of the nasal mucosa may induce protective reflexes in the upper airway in rats. Previously, we have reported that nasal air-jet stimulation increases the activities of the laryngeal muscles in decerebrate cats; however, the neuronal mechanism of this phenomenon still is not clarified.

METHODS

After the application of nasal air-jet stimulation for 2 hours, we investigated the distribution of Fos-positive cells (FPCs) throughout the medulla compared with sham-operated rats using Fos immunoreactivity.

RESULTS

FPCs in the spinal trigeminal nucleus, the parvocellular reticular nucleus, and the nucleus of the solitary tract were more frequent than the sham-operated rats.

CONCLUSION

These results suggest that the afferents induced by air-jet stimulation were conveyed to these FPCs and that some of these cells might participate in the augmentation of laryngeal muscle activities during nasal air-jet stimulation.

Nasal trigeminal inputs release the A5 inhibition received by the respiratory rhythm generator of the mouse neonate

Experiments were performed on neonatal mice to analyze why, in vitro, the respiratory rhythm generator (RRG) was silent and how it could be activated. We demonstrated that in vitro the RRG in intact brain stems is silenced by a powerful inhibition arising from the pontine A5 neurons through medullary alpha(2) adrenoceptors and that in vivo nasal trigeminal inputs facilitate the RRG as nasal continuous positive airway pressure increases the breathing frequency, whereas nasal occlusion and nasal afferent anesthesia depress it. Because nasal trigeminal afferents project to the A5 nuclei, we applied single trains of negative electric shocks to the trigeminal nerve in inactive ponto-medullary preparations. They induced rhythmic phrenic bursts during the stimulation and for 2-3 min afterward, whereas repetitive trains produced on-going rhythmic activity up to the end of the experiments. Electrolytic lesion or pharmacological inactivation of the ipsilateral A5 neurons altered both the phrenic burst frequency and occurrence after the stimulation. Extracellular unitary recordings and trans-neuronal tracing experiments with the rabies virus show that the medullary lateral reticular area contains respiratory-modulated neurons, not necessary for respiratory rhythmogenesis, but that may provide an excitatory pathway from the trigeminal inputs to the RRG as their electrolytic lesion suppresses any phrenic activity induced by the trigeminal nerve stimulation. The results lead to the hypothesis that the trigeminal afferents in the mouse neonate involve at least two pathways to activate the RRG, one that may act through the medullary lateral reticular area and one that releases the A5 inhibition received by the RRG.

The neuronal circuit of augmenting effects on intrinsic laryngeal muscle activities induced by nasal air-jet stimulation in decerebrate cats

We previously demonstrated that during nasal air-jet stimulation, both the activities of intrinsic laryngeal adductor and abductor muscles persistently increase, whereas the respiratory cycle prolongs and the activity of diaphragm decreases [Am. J. Rhinol. 9 (1995) 203-208; Neurosci. Res. 31 (1998) 137-146]. The purpose of this study was to clarify the neuronal circuit underlying the augmentation of intrinsic laryngeal muscles evoked by nasal air-jet stimulation. The immunohistologic analysis of Fos-expression was reported to determine the distribution of activated neurons in cat brainstem evoked by sneeze-inducing air puff stimulation of the nasal mucosa [Brain Res. 687 (1995) 143-154]. In sneezing cats, immunoreactivity was evoked in projection areas of the ethmoidal afferents, e.g. the subnuclei caudalis, interpolaris and in interstitial islands of the trigeminal sensory complex. Immunoreactivity was also enhanced in the solitary complex, the nucleus retroambiguus, the pontine parabrachial area and the lateral aspect of the parvocellular reticular formation [Brain Res. 687 (1995) 143-154]. In the present study, we focussed on the parvocellular reticular nucleus (PRN) as a relay of the neural circuit contributed to the augmentation of intrinsic laryngeal muscles evoked by nasal air-jet stimulation. We recorded the neuronal behavior of PRN during the nasal air-jet stimulation in precollicular-postmammillary decerebrate cats. As the results, 24% (17/71) of recorded neurons which were activated orthodromically by the electrical stimulation to anterior ethmoidal nerve, increased their firing rates in response to the nasal air-jet stimulation. Furthermore, spike-triggered averaging method revealed that four of these 17 PRN neurons activated intrinsic laryngeal muscles, suggesting that such neurons have excitatory projections to the intrinsic laryngeal muscle motoneurons in the nucleus ambiguus. These results suggest that the some of PRN neuron play a role in augmentation of the intrinsic laryngeal muscles activities during nasal air-jet stimulation.

Laryngeal muscle response to phasic and tonic upper airway pressure and flow

The hypothesis that respiratory modulation due to upper airway (UA) pressure and flow is dependent on stimulus modality and respiratory phase-specific activation was assessed in anesthetized, tracheotomized, spontaneously breathing piglets. Negative pressure and flow applied to the isolated UA at room or body temperature during inspiration only enhanced posterior cricoarytenoid muscle activity from that present without UA pressure and flow (baseline) by 15--20%. Time shifting the onset of UA flow relative to tracheal flow decreased this enhancement. The same enhancement was observed with oscillatory or constant airflow. UA positive pressure and flow at room or body temperature applied during expiration only enhanced thyroarytenoid muscle activity from baseline by 50--160%. The same enhancement was observed with oscillatory or constant airflow at body temperature. Constant positive pressure and flow enhanced thyroarytenoid muscle activity more than oscillatory pressure and flow at room temperature. We conclude that the respiratory modulation of UA afferents is processed in a phase-specific fashion and is dependent on stimulus modality (tonic vs. phasic).

Modulation of laryngeal and respiratory pump muscle activities with upper airway pressure and flow

The hypothesis that upper airway (UA) pressure and flow modulate respiratory muscle activity in a respiratory phase-specific fashion was assessed in anesthetized, tracheotomized, spontaneously breathing piglets. We generated negative pressure and inspiratory flow in phase with tracheal inspiration or positive pressure and expiratory flow in phase with tracheal expiration in the isolated UA. Stimulation of UA negative pressure receptors with body temperature air resulted in a 10--15% enhancement of phasic moving-time-averaged posterior cricoarytenoid electromyographic (EMG) activity above tonic levels obtained without pressure and flow in the UA (baseline). Stimulation of UA positive pressure receptors increased phasic moving-time-averaged thyroarytenoid EMG activity above tonic levels by 45% from baseline. The same enhancement of posterior cricoarytenoid or thyroarytenoid EMG activity was observed with the addition of flow receptor stimulation with room temperature air. Tidal volume and diaphragmatic and abdominal muscle activity were unaffected by UA flow and/or pressure, whereas respiratory timing was minimally affected. We conclude that laryngeal afferents, mainly from pressure receptors, are important in modulating the respiratory activity of laryngeal muscles.

Morphology of the glomerular nerve endings in the dorsal nasal ligament of the dog

The nasal atrium appears to be an important sensory site in the dog, yet no literature is available concerning its nerve supply. The present paper demonstrates the occurrence of glomerular nerve endings in the canine nasal atrium, using immunohistochemistry for neurofilament protein (NFP) and for glial fibrillary acidic protein (GFAP). Glomerular nerve endings occurred on the perichondrium of the septal and the dorsal lateral nasal cartilages, and their terminal portions were attached with dense collagen fibril strands of the dorsal nasal ligament. The glomerular endings were derived from a thick parent axon which branched repeatedly. Complicated winding nerve fibers gave rise to numerous thin filamentous terminals. Accumulations of GFAP immunoreactive glial cells were also observed. Immunoelectron microscopy for NFP revealed several axon terminals in the glomerular endings which contained numerous neurofilaments and mitochondria and were incompletely covered by Schwann cell sheaths. The glomerular endings in the dog nasal vestibule are suggested to perceive tensional changes in the nasal dorsal ligament caused by the opening of the nostrils and to be involved in the reflex regulating the activity of the nasal muscles.

Protective and defensive airway reflexes evoked by nasal exposure to wood smoke in anesthetized rats

We investigated the airway responses evoked by nasal wood smoke in anesthetized Sprague-Dawley rats. Wood smoke (5 ml, 1.4 ml/s) was delivered into an isolated nasal cavity while animals breathed spontaneously. In study 1, nasal wood smoke triggered either an apneic response (n = 26) or a sniff-like response (n = 16) within 1 s after smoke exposure in 42 normal rats. Both airway responses were abolished by trigeminal nerve denervation and by nasal application of a local anesthetic or a hydroxyl radical scavenger, but they were not significantly affected by removal of smoke particulates or nasal application of a saline vehicle. In study 2, nasal wood smoke only triggered a mild apneic response in two rats neonatally treated with capsaicin and had no effect on breathing in the other six; the treatment is known to chronically ablate C fibers and some Adelta fibers. In contrast, nasal wood smoke evoked an apneic response in six rats neonatally treated with the vehicle of capsaicin and elicited a sniff-like response in the other two. These results suggest that the apneic and sniff-like responses evoked by nasal wood smoke result from the stimulation of trigeminal nasal C-fiber and Adelta-fiber afferents by the gas-phase smoke and that hydroxyl radical is the triggering chemical factor.

Perceptual and physiologic effects of histamine challenge on nasal breathing

The purpose of this study is to determine the effect of histamine-induced nasal congestion on nasal airflow and the perception of externally applied resistance to nasal breathing. Nasal cross-sectional area and nasal airflow during free breathing were measured in 15 adult subjects before and after histamine challenge. The threshold for perception of resistance to nasal breathing was determined using a dynamic perturbator device, with both free breathing and controlled nasal air-flow. The average threshold for perception of nasal resistance was 0.383 Pa/cm3/s at baseline. After histamine application, there was a significant decrease in nasal cross-sectional area (p = 0.0001), associated with a decrease in nasal airflow (r = 0.6). The average threshold of perception increased to 1.373 Pa/cm3/s (p < 0.0001). When nasal airflow was controlled at the baseline rate, the threshold of perception improved to 0.638 Pa/cm3/s (p = 0.024). These findings indicate that nasal congestion causes a reduction in both nasal airflow and the perception of resistance to nasal breathing. The ability to detect nasal airway impairment is improved with increased nasal airflow. An improved understanding of the physiology of the subjective perception of nasal patency may lead to innovative methods for the treatment of nasal obstruction.

Age-related changes in the ventilatory response to inspired CO2 in neonatal rats

The objective of this study was to determine whether there is an age-related ventilatory response to transient increases in inspired CO2 in unanesthetized rat pups. Using plethysmography, ventilatory responses to 30 sec of 0, 2, 4, 6, and 8% inspired CO2 were measured in 21 rat pups from two litters. Recordings were made 1, 2, 3, 5, 7, 9 and 12 days after the day of birth (day 0). On day 1 there was a significant dose-related decrease in mean ventilatory frequency in response to each of the inspired CO2 concentrations. On day 2 there was no significant change in breathing frequency in response to 2 or 4% CO2 and a significant increase in frequency in response to 6 and 8% CO2. On days 3, 5, 7, 9 and 12 there was generally a significant increase in frequency in response to each of the inspired CO2 concentrations. Tidal volume was not significantly affected by the CO2 stimuli on any of the test days. Minute ventilation exhibited a significant decrease, on day 1, in response to 6 and 8% CO2. Litter, sex or weight of the rat pups was not correlated with the ventilatory depressions observed on day 1. These results show that in neonatal rats the ventilatory response to inspired CO2 is age-related and indicates a possible link between upper airway CO2 chemoreceptors, an inhibition of breathing, and SIDS.

The posterior nasal nerve plays an important role on cardiopulmonary reflexes to nasal application of capsaicin, distilled water and l-menthol in anesthetized dogs

The sensory innervation of the cardiopulmonary reflexes to nasal application of capsaicin (CAPS), distilled water (DW) and l-menthol (LM) was studied in anesthetized dogs breathing through tracheostomy. A marked cardiopulmonary reflex was observed by CAPS and DW into the nasal cavity, while a prolongation of expiration was induced by LM. All these reflexes were significantly decreased by bilateral section of the posterior nasal nerve (PNN) and completely abolished by topical nasal anesthesia with lidocaine. Responses of the whole nerve activity of the PNN to these substances corresponded to the magnitude of the reflexes. These results indicate that PNN afferents play an important role on the reflex elicitation of the noxious, water and cold stimuli from the nasal cavity.

Response of breathing pattern to flow and pressure in the upper airway of rats

The effects of upper airway (UAW) flows and pressures on breathing pattern and respiratory muscle activities were studied in anesthetized rats breathing through a tracheostomy. A steady flow (approximately 1000 ml/kg/min) of cold dry air, or cold wet air, or warm wet air was passed through the UAW, in the expiratory direction for approximately 20 sec (20-40 sec). In other trials positive or negative pressure was applied to the isolated UAW for a similar duration. There was a marked prolongation of the expiratory duration and decreases in peak inspiratory flow, tidal volume, and peak diaphragm electromyogram (EMG) activity in response to cold dry airflow. The responses to cold wet air were reduced but still significant. Warm wet air had no effect on breathing. These responses show that UAW cooling and drying depress breathing in the rat and that cooling itself could cause the inhibition of breathing. Negative pressure induced substantial increases in genioglossus and laryngeal inspiratory activity while positive pressure caused a decrease in genioglossus activity. Positive pressure also increased expiratory time while negative pressure increased inspiratory time. These results confirm the functional role of the UAW dilating muscles in preventing UAW from collapse in rats.

Nasal mechanoreceptors in guinea pigs

The characteristics of nasal mechanoreceptors in the ethmoidal nerve (EN) of guinea pigs were clarified by electrophysiological identification of their responsiveness to transmural pressure, i.e., the inspiratory effort induced by tracheal occlusion and probing of the nasal cavity, vestibule or alae nasi of the nose. A total of 73 mechanoreceptors were recorded from 18 guinea pigs breathing through the nose or a tracheostomy with an isolated nasal airway. Six receptors (6/22) in nasal-breathing animals were stimulated by upper airway occlusion, and 18 receptors (18/22) in tracheostomy-breathing animals were stimulated by maintained negative pressure in the nose. Mechanoreceptors responding to probing to the nose were found in both experimental set-ups. The mean threshold of 'pressure'-responsive receptors to negative pressure was very high (-3.87 +/- 0.95 kPa). Most of the receptors were also examined for response to ammonia vapour or instillation of distilled water; only three 'touch'-responsive receptors could be stimulated by ammonia and/or distilled water. These results suggest low sensitivity to pressure changes and noxious chemical stimuli of mechanoreceptors in the EN of guinea pigs.

The role of the temperature of the nasal lining in the sensation of nasal patency

The receptors and neural pathways involved in the common symptom of nasal blockage are of great interest. Studies to date suggest that the sensation of nasal patency may be related to the temperature of the nasal passages. Sixty-two subjects were asked to assess their own nasal patency subjectively and indicate this on a visual analogue scale. The temperature of the nasal lining was continuously recorded during quiet nasal respiration using a non-contact infrared thermometer. The cooler the nasal lining, the clearer the nose felt, and the greater the drop in temperature on inspiration again the clearer the nose felt. The study supports the previously proposed hypothesis that the sensation of nasal airflow is derived from a cooling of the nasal lining on inspiration, and this is probably detected by cold thermoreceptors in the mucosa.

Nasal receptors responding to cold and l-menthol airflow in the guinea pig

The aim of this study was to demonstrate the presence of nasal 'cold' receptors, through recordings of action potentials from the ethmoidal nerve (EN), in guinea pigs and to characterize their responsiveness to l-menthol and capsaicin. Constant flows (400 ml/min) of room air (20 degrees C), warm air (45 degrees C), room air containing l-menthol, and cold air (-5 degrees C) were directed into the nasal cavity in the inspiratory direction via a nasopharyngeal catheter in the anesthetized guinea pigs breathing spontaneously through a tracheostomy. The ethmoidal afferent activity was increased by cold air, and to a greater extent by l-menthol but hardly by warm air. After topical anesthesia of the nasal cavity with 2% lidocaine, cold air and l-menthol no longer stimulated the EN. L-menthol noticeably stimulated the EN even after repeated capsaicin instillation into the nose, but these values were lower than those following the l-menthol stimulus before the 1st capsaicin treatment. These results suggest that the ethmoidal nerve in guinea pigs has cold-sensitive receptors which consist of both small myelinated fibers and C-fiber endings.

Sensory information from the upper airway: role in the control of breathing

The functional integrity of extrathoracic airways critically depends on the proper orchestration of the activities of a set of patency-maintaining muscles. Recruitment and control of these muscles is regulated by a laryngeal and trigeminal affects that originate from pressure sensing endings. These sensors are particularly numerous among laryngeal receptors and, indeed, they constitute the main element in the respiration-modulated activity of the superior laryngeal nerve. Considering that the most compliant region of the upper airway, and thus more vulnerable to inspiratory collapse, lies cranially to the larynx, the laryngeal pressure-sensing endings seem to be ideally located for detecting collapsing forces and initiating reflex mechanisms for the preservation of patency. This process operates by activating upper airway dilating muscles and by decreasing inspiratory drive: both actions limit t he effect of the collapsing forces. Cold reception is differently represented in various mammalian species within nasal and laryngeal segments. Cooling of the upper airway has an inhibitory influence on breathing, especially in newborns, and a depressive effect on upper airway dilating muscles. The latter response is presumably mediated through the inhibitory effect of cooling on laryngeal pressure endings. These responses could be harmful during occlusive episodes. Powerful defensive responses with distinct characteristics can be elicited through the simulation of laryngeal and nasal irritant type receptors. Sneezing is elicited through the stimulation of trigeminal afferents, cough through the stimulation of laryngeal vagal endings. Changes in osmolality and ionic composition of the mucosal surface liquid can lead to conspicuous alterations in receptor activity and related reflexes.

Ventilatory and upper-airway resistance responses to upper-airway cooling and CO2 in anaesthetised rats

The effects of upper airway (UA) cool air and CO2 on breathing and on laryngeal and supraglottic resistances were studied in anaesthetised rats breathing spontaneously through a tracheostomy. Warm, humidified air containing 0, 5 and 9-10% CO2 and cool, room-humidity air were delivered at constant flow to either the isolated larynx to exit through a pharyngotomy or to the supraglottic UA to exit through the mouth and/or nose (nose open or sealed). Spontaneous tracheal airflow and UA airflows, temperatures and pressures were recorded. CO2 had no effect on breathing but caused a slight increase in laryngeal resistance which was abolished by cutting the superior laryngeal nerves (SLN). Cool air caused a decrease in respiratory frequency and/or peak inspiratory flow when applied to the isolated larynx or to the supraglottic airway with the nose closed. These effects were abolished by SLN section. With the nose open, the ventilatory inhibition was not abolished by SLN section. Cool air also caused substantial decreases in laryngeal and supraglottic resistances which were attenuated by SLN section and which persisted following recurrent laryngeal nerve section. In conclusion, whilst UA cooling inhibits breathing and decreases UA resistances, UA CO2 has minimal effects.

Nasal receptors responding to noxious chemical irritants

This study was performed to investigate the chemoreception of trigeminal afferents in the nose. Single unit activity was recorded from the anterior ethmoidal nerve in the anesthetized guinea pig breathing through a tracheostomy during nasal instillation of capsaicin (0.3 mM), nicotine (6 mM) and ammonia (1.5 M) solutions or with distilled water. Out of 36 fibers recorded, nineteen were stimulated by capsaicin, six by nicotine and seventeen by ammonia. Among those fibers, two were stimulated by both capsaicin and nicotine, six by both capsaicin and ammonia and one nicotine-responsive fiber was also stimulated by ammonia. A large proportion of capsaicin- and nicotine-responsive fibers exhibited long lasting discharges (170.4 +/- 17.7 sec and 120.7 +/- 29.3 sec, respectively), and were not stimulated by the second application of the same substance. However, fibers responding to ammonia discharged for a shorter time (31.5 +/- 6.5 sec), indicating a rapid adaptation. These results indicate that the ethmoidal nerve possesses a well-developed responsiveness to noxious stimuli. The nociceptive component of this nerve may be related to the various cardiorespiratory responses that can be elicited from the nasal cavity and also to local axonal reflexes (neurogenic inflammation) due to the release of chemical mediators from C-fiber endings.

Effect of route of breathing on the ventilatory and arousal responses to hypercapnia in awake and sleeping dogs

1. The influence of the upper airway on the ventilatory and arousal responses to hypercapnia in wakefulness and sleep was investigated using a chronic animal model. 2. Experiments were performed in five unrestrained dogs trained to sleep naturally in the laboratory. The animal rebreathed through a chronic tracheostoma (thus excluding the upper airway from the breathing circuit), or through the snout (intact upper airway). Resistance to breathing and volume of dead space during quiet tracheal breathing were matched to those in quiet nasal breathing during wakefulness and sleep. CO2 rebreathing tests were performed during wakefulness, rapid eye movement (REM) and non-REM (NREM) sleep, during nasal and tracheal breathing. 3. The ventilatory response to hypercapnia was significantly lower in nasal breathing compared with tracheal breathing, in all behavioural states. This was due to a smaller tidal volume and lower breathing frequency. 4. The ventilatory response to CO2 was lowest during REM sleep, irrespective of route used for breathing. 5. Alveolar partial pressure of CO2 (PA,CO2) level at arousal was identical in NREM nasal and tracheal rebreathing tests. Differences in PA,CO2 levels at arousal between NREM and REM sleep were not significant in nasal tests and only marginally different during tracheal breathing. 6. We conclude that nasal breathing influences the hypercapnic ventilatory response in wakefulness and sleep, and that the presence of CO2 in the upper airway does not affect arousal in NREM and REM sleep.

Nasal airflow receptors: the relative importance of temperature and tactile stimulation

The receptors responsible for the nasal sensation of airflow have not been identified with certainty. Although both mechanoreceptors and thermoreceptors have been implicated, evidence suggests that the nose is more sensitive to cold air than to air at body temperature. The present study was designed to investigate the relationship between the velocity and the temperature of an airjet as regards its ability to stimulate the nasal lining. Both the nasal vestibule and the nasal cavum are more sensitive to cold air than to air at mean intranasal temperature (P < 0.001). A similar effect is seen with warm air which is as stimulating as cold air. The nasal vestibule is twice as sensitive as the nasal cavum to an airjet at mean intranasal temperature (P < 0.001). It is concluded that the nasal vestible is very sensitive to the tactile stimulation of an airjet. This effect is highly temperature dependent being much more pronounced for air temperatures above or below the mean intranasal temperature. The temperature effect is relatively more important in the nasal cavum which is very much less sensitive to stimulation than the vestibule.

Menthol in the upper airway depresses ventilation in newborn dogs

Upper airway cooling depresses ventilation in the newborn dog. Since airway cooling stimulates laryngeal cold receptors and inhibits laryngeal mechanoreceptors, the type of afferent ending responsible for this reflex cannot be easily identified. l-menthol, a specific stimulant of cold receptors in the absence of any cooling, has been used to ascertain the discrete role of upper airway cold receptors in this ventilatory depression. Experiments were carried out in 8 anesthetized 7-14-day-old dogs breathing through a tracheostomy with the upper airway functionally isolated. Constant flows of warm air (37 degrees C), with and without addition of l-menthol, and cold air (25 degrees C) were delivered through the upper airway in the expiratory direction. As compared to warm air trials, cold air and warm air + l-menthol trials greatly reduced ventilation (57.5 +/- 10.7% and 52.8 +/- 11.7% of control, respectively; P less than 0.01) mostly due to a prolongation of Te (291.2 +/- 106.4% and 339.2 +/- 90.0%, respectively, P less than 0.01). Section of the superior laryngeal nerve abolished the response to cold air. However, a residual depressive effect of l-menthol was still present in 3 of 5 animals and was abolished by nasal anesthesia, suggesting the involvement of nasal cold receptors. The results suggest that in the newborn dog stimulation of laryngeal cold receptors, without any concurrent inhibition of laryngeal mechanoreceptors, is a sufficient stimulus to cause respiratory depression.

Airflow receptors in the lip and buccal mucosa

Airflow receptor afferents in the oral mucosa responding to changes in intraoral air pressure during blowing were found to be innervated by the infraorbital nerve. They provided one response corresponding to the onset of blowing, a second related to an increase in air pressure, a third corresponding to the cessation of blowing, and a fourth that exhibited little change throughout sustained blowing. Intraoral air pressure in the cavity between the lips and the velopharyngeal portal may be monitored by these receptors, and the data they provide may contribute to the control of phonation.

A comparative HRP study of the neuronal supply to the inferior and superior nasal meatus in the cat

Neurons supplying the nasal mucosa in the cat were retrogradely labelled with horseradish peroxidase. Sensory trigeminal neurons to the inferior and superior nasal meati are somatotopically organized, according to the ophthalmic or maxillary origin of the afferents studied. Whatever their relative location, the cell bodies from nasal afferents were, on average, smaller than the overall cell population in the ganglion, in keeping with the high proportion of nasal receptors innervated by thin fibers. Postganglionic neurons from parasympathetic origin could be labelled in the sphenopalatine ganglion. These neurons probably supply mucosal secretory glands. They are in the same size range as the bulk of neurons in the same ganglia.

The respiratory activity of the superior laryngeal nerve in the rat

The aim of this study was to characterize the laryngeal afferent activity of the rat. The animals were anesthetized and breathing spontaneously. Laryngeal afferent activity was recorded from both the whole superior laryngeal nerve (SLN) and from single fibers isolated from this nerve. An overall inspiratory augmenting activity was observed in the whole SLN during tracheostomy breathing, tracheal occlusion and upper airway breathing, but an expiratory augmenting activity was present during upper airway occlusion. The inspiratory modulated activity was abolished by bilateral section of the hypoglossal nerves but not the recurrent laryngeal nerves. A great number of receptors (46/80, 58%) were identified as 'drive' receptors, and others as 'pressure' (22/80, 28%) and 'irritant' type receptors (9/80, 11%). Nineteen pressure receptors were stimulated by positive transmural pressure, while only three stimulated by negative pressure. Nine drive receptors were also stimulated by positive pressure and inhibited by negative pressure. Such response to pressure was further evaluated by applying maintained pressures to the functionally isolated upper airway. These results are essentially consistent with findings obtained in the rabbit, but differ from those reported for the dog.

Afferent activity in the external branch of the superior laryngeal and recurrent laryngeal nerves

We investigated the presence of respiratory-modulated receptors in the recurrent laryngeal nerve (RLN) and the external branch of the superior laryngeal nerve (ExtSLN) in anesthetized, spontaneously breathing dogs. Of 39 receptors recorded from the ExtSLN, the vast majority responded with a slowly adapting discharge to compression of the cricothyroid muscle, and only 1 responded to probing of the laryngeal mucosa. Ten receptors showed a respiratory modulation. All 30 receptors recorded from the RLN responded to probing of the laryngeal lumen, most of them (60%) with a rapidly adapting response. Seven of the slowly adapting receptors exhibited a respiratory modulation; 38% of the receptors tested were stimulated by water, and only 15% by smoke. No receptors stimulated by laryngeal cooling were identified in either nerve. Our study indicates that in the RLN and the ExtSLN there are relatively few afferents responding to changes in transmural pressure and mechanical irritation, as compared to the internal branch of the SLN. The relative scarcity of receptors responding to transmural pressure and irritant stimuli is consistent with previous observations in dogs that indicate a preponderant role for afferents in the internal branch of the SLN in the reflex responses to laryngeal stimulation.

Trigeminal nasal receptors related to respiration and to various stimuli in cats

In twenty adult cats of either sex under nembutal anaesthesia, we aimed at delineating the sensitive territory of trigeminal nerves innervating the nasal mucosa. The different trigeminal nerves (anterior ethmoidal, posterior nasal and infraorbital nerves) were dissected in the orbit. Activity of these nerves was recorded during spontaneous nasal and tracheal breathing and in response to various stimuli: mechanical (manual probing and air jets) and irritants (ammonia vapours). Multiple and unitary activity recorded in nerve filaments enabled a classification of the receptors on the basis of their discharge pattern as rapidly-, intermediately- or slowly adapting receptors, and as drive or non-drive nasal receptors depending on whether or not the respiratory modulation was preserved during tracheal breathing.

Cooling mediates the ventilatory depression associated with airflow through the larynx

Although constant airflow through the upper airway has been shown to induce ventilatory depression in anesthetized newborn animals, the role of laryngeal temperature in this response has not been studied. Experiments were performed in fourteen 1-5 day-old anesthetized puppies breathing through a tracheostomy. Tidal volume and laryngeal temperature were recorded while a constant stream of air (15-25 ml/sec) at room temperature was passed in the expiratory direction for 20 sec through the isolated upper airway. Warm (35-37 degrees C), humidified air at the same flow served as control. When laryngeal temperature was decreased by 7.5 +/- 0.9 degrees C, a marked change in breathing pattern was observed (VT = 54 +/- 5, TI = 187 +/- 33, TE = 636 +/- 179, VT/TI = 45 +/- 10% of control; n = 9). Warm air at the same flow induced no significant changes. Superior laryngeal nerve section abolished the effects of cooling on breathing pattern. In 5 puppies we compared the effect of 'fast' and 'slow' laryngeal cooling. Fast trials altered breathing pattern earlier than slow trials. We conclude that the depressant effect of airflow through the upper airway is entirely due to a decrease in laryngeal temperature and is mediated by superior laryngeal nerve afferents.

The effects of oral administration of (-)-menthol on nasal resistance to airflow and nasal sensation of airflow in subjects suffering from nasal congestion associated with the common cold

The effects of oral administration of a lozenge containing 11 mg (-)-menthol on nasal resistance to airflow (NAR) and nasal sensation of airflow in 62 subjects suffering from nasal congestion associated with naturally acquired common cold infection have been studied. NAR was measured by posterior rhinomanometry and nasal sensation of airflow by means of a visual analogue scale (VAS). The effects of the lozenge were compared with a candy placebo lozenge in a double blind randomized trial. NAR showed a significant increase (P less than 0.05) in both the menthol and placebo groups over the 2 h experiment with no difference between the groups at any time. The VAS scores showed significant changes of subjective improvement in nasal sensation of airflow (P less than 0.001) in the menthol-treated group 10 min after dosing whereas the placebo group showed no change. It is concluded that dosing with 11 mg menthol in subjects with common cold has no effect on NAR as measured by posterior rhinomanometry but causes a marked change in nasal sensation of airflow with a subjective sensation of nasal decongestion.