Mechanoreceptors in the nose

The effects of maxillary nerve block, ethmoidal nerve block and their combination on cardiopulmonary responses to nasal stimulation in anesthetized Beagle dogs

OBJECTIVE

To describe an approach for ethmoidal nerve block (E_BLOCK) and to compare the effects of a maxillary nerve block (M_BLOCK), E_BLOCK and their combination (M-E_BLOCK) on heart rate (HR), systolic (SAP), mean (MAP), diastolic (DAP) arterial pressures and respiratory rate (f_R) during nasal stimulation in dogs.

STUDY DESIGN

Prospective, blinded, randomized, crossover placebo-controlled study.

ANIMALS

Beagle dogs (five cadavers, nine live dogs), with a median (interquartile range) weight of 10.5 (10.3-11.0) kg.

METHODS

The accuracy of iohexol injections (each 1 mL) at the maxillary and ethmoidal foramina in cadavers was evaluated using computed tomography. Then, anesthetized dogs were administered four bilateral treatments separated by 1 week, saline or 2% lidocaine 1 mL per injection: injections of saline at the maxillary and ethmoidal foramina (Control), injections of lidocaine at the maxillary foramina and saline at the ethmoidal foramina (M_BLOCK), injections of saline at the maxillary foramina and lidocaine at the ethmoidal foramina (E_BLOCK) and injections of lidocaine at all foramina (M-E_BLOCK). The ventral nasal meatus was bilaterally stimulated using cotton swabs, and HR, SAP, MAP, DAP and f_R were continuously recorded. Values for each variable were compared before and after stimulation using Wilcoxon signed-rank test. Changes in variables among treatments were analyzed using Mann-Whitney U and Kruskal-Wallis tests (p ≤ 0.05).

RESULTS

Computed tomography revealed iohexol distribution around the openings of the target foramina in all cadavers. In living dogs, HR, SAP, MAP, DAP and f_R significantly increased after stimulation within each treatment (p < 0.03). Physiologic responses were significantly attenuated, but not absent, in the M-E_BLOCK [HR (p = 0.019), SAP, MAP, DAP and f_R (all p ≤ 0.001)] compared with those in the Control.

CONCLUSIONS AND CLINICAL RELEVANCE

Concurrent injections of lidocaine at the maxillary and ethmoidal foramina attenuated HR, arterial pressure and f_R responses to nasal stimulation in Beagle dogs.

Effect of airway surface liquid on the forces on the pharyngeal wall: Experimental fluid-structure interaction study

Obstructive sleep apnoea syndrome (OSAS) is a breathing disorder with a multifactorial etiology. The respiratory epithelium is lined with a thin layer of airway surface liquid preventing interactions between the airflow and epithelium. The effect of the liquid lining in OSAS pathogenesis remains poorly understood despite clinical research. Previous studies have shown that the physical properties of the airway surface liquid or altered stimulation of the airway mechanoreceptors could alleviate or intensify OSAS; however, these studies do not provide a clear physical interpretation. To study the forces transmitted from the airflow to the liquid-lined compliant wall and to discuss the effects of the airway surface liquid properties on the stimulation of the mechanoreceptors, a novel and simplified experimental system mimicking the upper airway fundamental characteristics (i.e., liquid-lined compliant wall and complex unsteady airflow features) was constructed. The fluctuating force on the compliant wall was reduced through a damping mechanism when the liquid film thickness and/or the viscosity were increased. Conversely, the liquid film damping was reduced when the surface tension decreased. Based on the experimental data, empirical correlations were developed to predict the damping potential of the liquid film. In the future, this will enable us to extend the existing computational fluid-structure interaction simulations of airflow in the human upper airway by incorporating the airway surface liquid effect without adopting two-phase flow interface tracking methods. Furthermore, the experimental system developed in this study could be used to investigate the fundamental principles of the complex once/twice-coupled physical phenomena.