Rheological properties controlling mucociliary frequency and respiratory mucus transport

Respiratory mucus and mucosa possess highly hydrophilic structures which are difficult to preserve using standard fixative methods. The close interaction between cilia and mucus can be observed after instantaneously interrupting the ciliary movement using ultra rapid and cryosubstitution fixation methods. Mucus possess several rheological properties such as pseudoplasticity, elastothixotropy, spinability and adhesiveness. Rheological properties of mucus may control, per se, the ciliary beating frequency. By measuring the mucociliary frequency on the excised mucus-depleted frog palate of native mucus and xanthan gum using a simulant of mucus, we observed that beyond an optimal value of viscosity (close to 12 Pa.s) the mucociliary frequency and transport rate decrease in parallel. Other rheological factors such as adhesion and spinability of mucus can also be implicated in the regulation of the mucociliary transport rate.     

Induction of ciliary orientation by matrix patterning and characterization of mucociliary transport

Impaired mucociliary clearance (MCC) is a key feature of many airway diseases, including asthma, bronchiectasis, chronic obstructive pulmonary disease, cystic fibrosis, and primary ciliary dyskinesia. To improve MCC and develop new treatments for these diseases requires a thorough understanding of how mucus concentration, mucus composition, and ciliary activity affect MCC, and how different therapeutics impact this process. Although differentiated cultures of human airway epithelial cells are useful for investigations of MCC, the extent of ciliary coordination in these cultures varies, and the mechanisms controlling ciliary orientation are not completely understood. By introducing a pattern of ridges and grooves into the underlying collagen substrate, we demonstrate for the first time, to our knowledge, that changes in the extracellular matrix can induce ciliary alignment. Remarkably, 90% of human airway epithelial cultures achieved continuous directional mucociliary transport (MCT) when grown on the patterned substrate. These cultures maintain transport for months, allowing carefully controlled investigations of MCC over a wide range of normal and pathological conditions. To characterize the system, we measured the transport of bovine submaxillary gland mucin (BSM) under several conditions. Transport of 5% BSM was significantly reduced compared with that of 2% BSM, and treatment of 5% BSM with the reducing agent tris(2-carboxyethyl)phosphine (TCEP) reduced viscosity and increased the rate of MCT by approximately twofold. Addition of a small amount of high-molecular-weight DNA increased mucus viscosity and reduced MCT by ～75%, demonstrating that the composition of mucus, as well as the concentration, can have significant effects on MCT. Our results demonstrate that a simple patterning of the collagen substrate results in highly coordinated ciliated cultures that develop directional MCT, and can be used to investigate the mechanisms controlling the regulation of ciliary orientation. Furthermore, the results demonstrate that this method provides an improved system for studying the effects of mucus composition and therapeutic agents on MCC.     

Cholinergic nerves stimulate mucociliary transport,ciliary activity,and mucus secretion in the frog palate

Summary Mucociliary transport, ciliary activity, and mucus secretion were studied in the palate of the frog Rana pipiens by direct observation, stroboscopic synchronization of ciliary beating, and histochemistry. Excised palates were studied in vitro, and intact palates were studied in vivo. Electrical stimulation of the glossopharyngeal nerve in vivo or of the palatine nerve in vitro stimulated all three activities. The effect was mimicked by acetylcholine and pilocarpine, enhanced by physostigmine, and blocked by atropine but unaffected by d-tubocurarine. Stimulation increased the number of cilia beating and their rate of beating, the number of goblet cells secreting and, for small acidic cells, the amount of mucus secreted, and the rate and extent of particle transport. The response to tactile stimulation was locally restricted in vitro but widespread in vivo. It was concluded that, although there is a low basal rate of mucus secretion and ciliary activity that is independent of nervous control, stimulation of these activities in the intact animal is mediated through the central nervous system and cholinergic nerves to the palate.Supported in part by Grant HL-16730 from the U.S. Public Health Service     

Neuronal control of pedal sole cilia in the pond snail Lymnaea stagnalis appressa

5-HT (serotonin) is a ubiquitous neurotransmitter that produces ciliary beating in gastropods when applied topically, but ciliary beating caused by gastropod serotonergic neurons has been described in only three neuron pairs. We extend these results to the North American Lymnaea stagnalis appressa, which is a different species from the European Lymnaea stagnalis. We describe a non-serotonergic neuron pair, PeV1, which accelerates pedal sole mucociliary transport and a serotonergic neuron pair, PeD7, which slows mucociliary transport. We compare and discuss development and identified neurons in L. s. appressa and in L. stagnalis, which have homologs to L. s. appressa PeD7 and PeV1 neurons. In addition to PeD7 and PeV1 neurons, we test neurons immunoreactive to Tritonia pedal peptide antibodies with negative results for mucociliary transport. In characterizing PeD7 and PeV1 neurons, we find that PeV1 does not excite PeD7. In semi-intact preparations, a strong increase in PeD7 neuron activity occurs during tactile stimulation, but V1 neurons are inhibited during tactile stimulation. Following tactile stimulation, PeV1 neurons show strong activity. This suggests a distinct difference in function of the two neuron pairs, which both have their axons overlying pedal sole ciliary cells. Application of 5-HT to the pedal sole initiates mucociliary transport in 1.4–1.9 s with a time course similar to that seen when stimulating a PeV1 neuron. This result appears to be through a 5-HT_1A-like receptor on the pedal sole. We describe a possible external source of 5-HT on the pedal sole from 5-HT immunoreactive granules that are released with mucus.     

The forces applied by cilia depend linearly on their frequency due to constant geometry of the effective stroke

Mucus propelling cilia are excitable by many stimulants, and have been shown to increase their beating frequency up to threefold, by physiological extracellular stimulants, such as adenosine-triphosphate, acetylcholine, and others. This is thought to represent the evolutionary adaptation of mucociliary systems to the need of rapid and efficient cleansing the airways of foreign particles. However, the mucus transport velocity depends not only on the beat frequency of the cilia, but on their beat pattern as well, especially in the case of mucus bearing cilia that beat in a complex, three-dimensional fashion. In this study, we directly measured the force applied by live ciliary tissues with an atomic force microscope, and found that it increases linearly with the beating frequency. This implies that the arc swept by the cilia during their effective stroke remains unchanged during frequency increase, thus leading to a linear dependence of transport velocity on the beat frequency. Combining the atomic force microscope measurements with optical measurements, we have indications that the recovery stroke is performed on a less inclined plane, leading to an effective shortening of the overall path traveled by the cilia tip during this nontransporting phase of their beat pattern. This effect is observed to be independent of the type of stimulant (temperature or chemical), chemical (adenosine-triphosphate or acetylcholine), or concentration (1 μM-100 μM), indicating that this behavior may result from internal details of the cilium mechanical structure.     

Development of mucociliary transport in the postnatal ferret trachea.

Little is known of the developmental aspects of mucociliary transport. Previous studies have documented that newborn ferret trachea has very few ciliated cells but numerous immature secretory cells in the epithelium and only rudimentary submucosal glands. Rapid and complete maturation occurs in the first postnatal month. This study examines mucociliary transport during this period of rapid maturation. We made direct observations of particle movement across the epithelium of ferret tracheas. No mucus transport could be demonstrated on the first day of life. Transport was discernible, although sporadic and slow, by 7 days and reached adult levels (10.7 +/- 3.7 mm/min) by 28 postnatal days. The emergence of transport capability correlated well with previously described developmental changes in ciliation, mucus secretion, and ion permeability and transport. Threshold mucus transport occurred at 1 wk of age when 20-25% of the surface cells are ciliated. The neonatal ferret appears to be a useful model for assessing integrated epithelial structure-function relationships that are important not only during early development but also during repair after airway injury involving deciliation.     

Hyaluronan blocks porcine pancreatic elastase-induced mucociliary dysfunction in allergic sheep.

Neutrophil elastase is a mediator common to asthma, chronic obstructive pulmonary disease, and cystic fibrosis and thought to contribute to the pathophysiology of these diseases. Previously, we found that inhaled hyaluronan blocked elastase-induced bronchoconstriction in allergic sheep through its control of tissue kallikrein. Here, we extend those studies by determining if inhaled hyaluronan can protect against the elastase-induced depression in tracheal mucus velocity, a surrogate marker of whole lung mucociliary clearance. We measured tracheal mucus velocity in allergic sheep before, and sequentially for 6 h after, aerosol challenge with porcine pancreatic elastase alone and after pretreatment with 1.5 or 6 mg aerosolized hyaluronan. Elastase (2.55 U) decreased tracheal mucus velocity. Pretreatment with 6 mg, but not 1.5 mg, hyaluronan inhibited the elastase-induced decrease in tracheal mucus velocity. Hyaluronan (6 mg) given 1 h after elastase challenge was ineffective, suggesting the involvement of secondary mediators. The elastase-induced depression in mucus transport appeared to be mediated, in part, by reactive oxygen species and bradykinin because pretreatment with either aerosolized catalase (38 mg/3 ml) or the bradykinin B2-receptor antagonist HOE140 (400 nM/kg) was also effective in blocking the response. These latter two findings are consistent with oxygen radical-induced degradation of hyaluronan with concomitant loss of its regulatory effect on tissue kallikrein, resulting in kinin generation. This hypothesis is supported by the demonstration that hyaluronan failed to block the oxygen radical-induced fall in tracheal mucus velocity resulting from xanthine-xanthine oxidase challenge and that inhaled bradykinin itself can slow mucociliary transport.     

Effect of Pseudomonas aeruginosa rhamnolipids on mucociliary transport and ciliary beating.

Pseudomonas aeruginosa rhamnolipid causes ciliostasis and cell membrane damage to rabbit tissue, is a secretagogue in cats, and inhibits epithelial ion transport in sheep tissue. It could therefore perturb mucociliary clearance. We have investigated the effect of rhamnolipid on mucociliary transport in the anesthetized guinea pig and guinea pig and human respiratory epithelium in vitro. Application of rhamnolipid to the guinea pig tracheal mucosa reduced tracheal mucus velocity (TMV) in vivo in a dose-dependent manner: a 10-microgram bolus caused cessation of TMV without recovery; a 5-micrograms bolus reduced TMV over a period of 2 h by 22.6% (P = 0.037); a 2.5-microgram bolus caused no overall changes in TMV. The ultrastructure of guinea pig tracheal epithelium exposed to 10 micrograms of rhamnolipid in vivo was normal. Application of 1,000 micrograms/ml rhamnolipid had no effect on the ciliary beat frequency (CBF) of guinea pig tracheal rings in vitro after 30 min, but 250 micrograms/ml stopped ciliary beating after 3 h. Treatment with 100 micrograms/ml rhamnolipid caused immediate slowing of the CBF (P less than 0.01) of human nasal brushings (n = 7), which was maintained for 4 h. Mono- and dirhamnolipid had equivalent effects. The CBF of human nasal turbinate organ culture was also slowed by 100 micrograms/ml rhamnolipid, but only after 4 h (CBF test, 9.87 +/- 0.41 Hz; control, 11.48 +/- 0.27 Hz; P less than 0.05, n = 6), and there was subsequent recovery by 14 h.(ABSTRACT TRUNCATED AT 250 WORDS)     

Method for Quantitative Study of Airway Functional Microanatomy Using Micro-Optical Coherence Tomography

We demonstrate the use of a high resolution form of optical coherence tomography, termed micro-OCT (μOCT), for investigating the functional microanatomy of airway epithelia. μOCT captures several key parameters governing the function of the airway surface (airway surface liquid depth, periciliary liquid depth, ciliary function including beat frequency, and mucociliary transport rate) from the same series of images and without exogenous particles or labels, enabling non-invasive study of dynamic phenomena. Additionally, the high resolution of μOCT reveals distinguishable phases of the ciliary stroke pattern and glandular extrusion. Images and functional measurements from primary human bronchial epithelial cell cultures and excised tissue are presented and compared with measurements using existing gold standard methods. Active secretion from mucus glands in tissue, a key parameter of epithelial function, was also observed and quantified.     

A numerical study of muco-ciliary transport under the condition of diseased cilia

Structural and functional disorders of pulmonary cilia may result from genetic disorders and acquired insults. A two-dimensional numerical model based on the immersed boundary method coupled with the projection method is used to study the flow physics of muco-ciliary transport of the human respiratory tract under various abnormalities of cilia. The effects of the cilia beat pattern (CBP), ciliary length, immotile cilia, beating amplitude and uncoordinated beating of cilia are investigated. As expected, the mucus velocity decreases as the beating amplitude reduces. The windscreen wiper motion and rigid planar motion, which are two abnormal CBPs owing to genetic disorders, greatly reduce or almost stop the mucus transport. If the ciliary length varies from its standard length, the mucus velocity would decrease. The mucus velocity decreases rather linearly if the number of uniformly distributed immotile cilia increases. The numerical results show that the mucus velocity would be further reduced marginally when the uniformly distributed immotile cilia are rearranged as a cluster of immotile cilia. Furthermore, if half of the cilia are immotile and uniformly distributed and motile cilia beat at reduced amplitude, the incoordination between the active motile cilia would not significantly affect the mucus velocity.     

A follow-up study of mucociliary clearance and trace element and mineral status in children with chronic rhinosinusitis before and three months after endoscopic sinus surgery

BackgroundThe existing data demonstrate the potential role of trace elements in nasal mucociliary clearance, although the association between trace element and mineral status and ciliary function in children with chronic rhinosinusitis is insufficiently studied. Therefore, the objective of the present study is evaluation of trace element and mineral status and mucociliary function in pediatric CRS patients before and after functional endoscopic sinus surgery.MethodsThe present study involved 30 children with chronic rhinosinusitis without nasal polyps. During this follow-up the patients were examined preoperatively (point 0), underwent functional endoscopic sinus surgery, and were repeatedly examined at three months postoperatively (point 1). At both points the patients were subjected to quality-of-life assessment using SNOT-20 questionnaire; endoscopic and computer tomography examination of the nasal sinuses; evaluation of ciliary function and mucosal cytology using high-speed videomicroscopy; assessment of blood count and inflammatory markers; as well as analysis of trace element and mineral levels in whole blood, serum, and hair using inductively-coupled plasma mass-spectrometry.ResultsThe obtained data demonstrate that endoscopic sinus surgery significantly improved sinonasal pathology in children with chronic rhinosinusitis, as evidenced by significantly reduced Lund-Mackay, Lund-Kennedy, and SNOT-20 scores. At the same time, no significant improvement of ciliary functions or mucosal cytology was observed postoperatively. Trace element status assessment demonstrated that postoperative serum Zn, whole blood Mg and Cu were significantly lower as compared to preoperative values. In contrast, serum Mn and Cr, as well as whole blood Cr and hair Se were characterized by a significant increase at three months postoperatively. Multiple linear regression analysis demonstrated that serum Zn is significantly associated with the number of ciliated cells and cell viability, whereas serum Mn and whole blood Cu concentrations are inversely associated with cell viability and ciliary length, respectively. Hair Se was found to be associated with the number of neutrophils in the mucosa biopsy.ConclusionRedistribution of trace elements and minerals may at least partially mediate prolonged recovery of mucosal ciliary function in children with chronic rhinosinusitis in three months after functional sinus surgery, although the particular mechanisms of these alterations in trace element levels are to be discovered.     

Mucociliary interaction in vitro: effects of physiological and inflammatory stimuli

Mucociliary transport in the airways is governed by the interaction between ciliary activity and the depth and rheological properties of the liquids (mucus) covering the epithelial surface. A change in one of these parameters may not predict the direction and magnitude of a concomitant change in mucociliary transport. We therefore determined the effects of physiological (neurotransmitters) and pathological (inflammatory mediators) stimuli on ciliary beat frequency (CBF), surface liquid velocity (SLV), surface liquid depth (SLD), and viscoelasticity of mucus in pieces of sheep trachea (n = 5 for each treatment) mounted in a chamber such that the submucosal side was bathed with Krebs-Henseleit perfusate (KH) and the luminal side was exposed to conditioned air. SLV, SLD, and CBF were measured with a microscope provided with an electronic micrometer and strobe light. Apparent viscosity and shear elastic modulus were measured with a microcapillary method using mucus collected at the downstream end of the preparation. Control CBF, SLV, and SLD were 11.6 +/- 0.4 (SE) Hz, 91 +/- 8 micron/s, and 33 +/- 5 microns, respectively, at base line and did not change during KH perfusion for 100 min. Perfusion with both acetylcholine and epinephrine (10(-5) to 10(-3) M) produced concentration-dependent increases in mean CBF (maximum increases at 10(-3) M of 16 and 9%, P less than 0.05), whereas only acetylcholine increased mean SLV (+56% at 10(-3) M, P less than 0.05). Perfusion with platelet-activating factor (10(-7) to 10(-5) M) decreased both mean CBF and SLV in a dose-dependent fashion (-6 and -63% at 10(-5) M, P less than 0.05), whereas antigen perfusion (1:60 dilution) increased mean CBF (+10%, P less than 0.05) but decreased SLV (-47%, P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Numerical and experimental investigation of mucociliary clearance breakdown in cystic fibrosis

The human tracheobronchial tree surface is covered with mucus. A healthy mucus is a heterogeneous material flowing toward the esophagus and a major defense actor against local pathogen proliferation and pollutant deposition. An alteration of mucus or its environment such as in cystic fibrosis dramatically impacts the mucociliary clearance. In the present study, we investigate the mechanical organization and the physics of such mucus in human lungs by means of a joint experimental and numerical work. In particular, we focus on the influence of the shear-thinning mucus mobilized by a ciliated epithelium for mucociliary clearance. The proposed robust numerical method is able to manage variations of more than 5 orders of magnitude in the shear rate and viscosity. It leads to a cartography that allows to discuss major issues on defective mucociliary clearance in cystic fibrosis. Furthermore, the computational rheological analysis based on measurements shows that cystic fibrosis shear-thinning mucus tends to aggregate in regions of lower clearance. Yet, a rarefaction of periciliary fluid has a greater impact than the mucus shear-thinning effects.     

Effects of dry air and subsequent humidification on tracheal mucous velocity in dogs.

The impairment of mucociliary transport by dry air breathing and the restoration of function with subsequent humidification of inspired air were investigated in anesthetized dogs. Tracheal mucous velocity was measured by a cinebronchofiberscopic technique. The breathing of dry air through an uncuffed endotracheal tube produced almost complete cessation of the flow of tracheal mucus after 3 h. Subsequent breathing of air at 38 degrees C with 100% relative humidity restored tracheal mucous velocity to control values by the end of and additional 3 h. Histologic examination of the trachea at the end of the 3-h dry air breathing period revealed focal areas of sloughing of the ciliated epithelium and submucosal inflammation. Although morphometry was not employed, the inflammatory changes appeared to have progressed during 3 h of breathing fully humidified air subsequent to the dry air breathing period. These findings were consistent with previous reports that the inflammatory response to injury of the tracheobronchial mucosa might be delayed and that the mucociliary transport system has a great deal of functional reserve. We found that an artificial heat and moisture exchanger placed on the proximal end of an endotracheal tube partially protects against the suppression of tracheal mucous velocity caused by dry air breathing.     

Muco-ciliary transport in the lung

A two-layer Newtonian fluid model for muco-ciliary transport in the lung is developed where the viscosity of the upper mucous layer is very much greater than the viscosity of the lower periciliary layer. Theory is presented for both cases when the cilia penetrate, and do not penetrate, the very viscous mucous layer. Calculations suggest that, in normal circumstances, it is not essential for the cilia to penetrate the mucus to provide positive transport. However, it does suggest that there is a weak optimal penetration depth of the cilia of between 10-20% of the cilium length. In the case of high ciliary inactivity (e.g. 90% inactive), penetration of cilia into the mucus is essential for normal transport rates suggesting the mucociliary system may be deliberately overdesigned to cater for a whole range of pathological circumstances.     

Ozone exposure alters tracheobronchial mucociliary function in humans

Mucociliary function is a primary defense mechanism of the tracheobronchial airways, and yet the response of this system to an inhalational hazard, such as ozone, is undefined in humans. Utilizing noninvasive techniques to measure deposition and retention of insoluble radiolabeled particles on airway mucous membranes, we studied the effect on mucus transport of 0.2 and 0.4 ppm ozone compared with filtered air (FA) in seven healthy males. During 2-h chamber exposures, subjects alternated between periods of rest and light exercise with hourly spirometric measurement of lung function. Mechanical and mucociliary function responses to ozone by lung airways appeared concentration dependent. Reduction in particle retention was significant (P less than 0.005) (i.e., transport of lung mucus was increased during exposure to 0.4 ppm ozone and was coincident with impaired lung function; e.g., forced vital capacity and midmaximal flow rate fell by 12 and 16%, respectively, and forced expiratory volume at 1 s by 5%, of preexposure values). Regional analysis indicated that mucus flow from distal airways into central bronchi was significantly increased (P less than 0.025) by 0.2 ppm ozone. This peripheral effect, however, was buffered by only a marginal influence of 0.2 ppm ozone on larger bronchi, such that the resultant mucus transport for all airways of the lung in aggregate differed only slightly from FA exposures. These data may reflect differences in regional diffusion of ozone along the respiratory tract, rather than tissue sensitivity. In conclusion, mucociliary function of humans is acutely stimulated by ozone and may result from fluid additions to the mucus layer from mucosal and submucosal secretory cells and/or alteration of epithelial permeability.     

A new paradigm in respiratory hygiene: modulating respiratory secretions to contain cough bioaerosol without affecting mucus clearance

Background

Several strategies and devices have been designed to protect health care providers from acquiring transmissible respiratory diseases while providing care. In modulating the physical characteristics of the respiratory secretions to minimize the aerosolization that facilitates transmission of airborne diseases, a fundamental premise is that the prototype drugs have no adverse effect on the first line of respiratory defense, clearance of mucus by ciliary action.

Methods

To assess and demonstrate the primary mechanism of our mucomodulators (XLs), we have built our evidence moving from basic laboratory studies to an ex-vivo model and then to an in-vivo large animal model. We exposed anesthetized dogs without hypersecretion to different dose concentrations of aerosolized XL "B", XL "D" and XL "S". We assessed: cardio-respiratory pattern, tracheal mucus clearance, airway patency, and mucus viscoelastic changes.

Results

Exposure of frog palate mucus to XLs did not affect the clearance of mucus by ciliary action. Dogs maintained normal cardio-respiratory pattern with XL administration. Tracheal mucociliary clearance in anesthetized dogs indicated a sustained 40% mean increase. Tracheal mucus showed increased filance, and there was no mucus retention in the airways.

Conclusion

The ex-vivo frog palate and the in-vivo mammalian models used in this study, appear to be appropriate and complement each other to better assess the effects that our mucomodulators exert on the mucociliary clearance defence mechanism. The physiological function of the mucociliary apparatus was not negatively affected in any of the two epithelial models. Airway mucus crosslinked by mucomodulators is better cleared from an intact airway and normally functioning respiratory system, either due to enhanced interaction with cilia or airflow-dependent mechanisms. Data obtained in this study allow us to assure that we have complied with the fundamental requirement criteria established in the initial phase of developing the concept of mucomodulation: Can we modulate the physical characteristics of the respiratory secretions to reduce aerosolization without affecting normal mucociliary clearance function, or even better improving it?     

The role of mucus gel viscosity, spinnability, and adhesive properties in clearance by simulated cough

We investigated the role of the viscoelastic and adhesive properties of mucus gel simulants on the clearance of mucus by simulated cough. Mucus-like gels with widely varying viscoelastic properties were prepared from polysaccharides crosslinked with sodium borate. Cough was simulated by opening a solenoid valve connecting a model trachea to a pressurized tank. The clearance of gels lining the model trachea was quantified by observing marker particle transport. Viscosity elastic modulus, relaxation time and yield stress were measured with a steady-shear viscoelastometer. Spinnability (thread formation) was determined with a filancemeter. Adhesivity (surface tension) was measured by the platinum ring technique. The viscoelastic and adhesive properties of the mucus gel simulants spanned the ranges observed for bronchial secretions from patients with COPD. The relationship between simulated cough clearance and the viscoelastic and adhesive properties of the gels was analyzed by stepwise linear regression of the non-zero data matrix. The major independent variable relating to clearance was viscosity. Secondary, but highly significant dependences, were also found for spinnability and adhesivity. Elastic modulus, relaxation time and yield stress had no independent effect on cough clearance over the investigated range. The results indicate that, in the absence of airway surface liquid, cough-type clearance relates primarily with mucus gel viscosity. For a given viscosity, clearance is also impaired by spinnability, i.e. the capacity of the mucus to form threads. At constant viscosity and spinnability, clearance is further impaired by an increase in the adhesivity of the mucus. The negative dependence of each of these physical factors can be rationalized in terms of their inhibitory effect on wave formation in the mucus lining layer during high velocity airflow interaction.     

Airway responses to esophageal acidification

The effects of esophageal acidification on airway function are unclear. Some have found that the esophageal acidification causes a small increase in airway resistance, but this change is too small to cause significant symptoms. The aims of this study were to investigate the effects of esophageal acidification on multiple measures of airway function in chloralose-anesthetized cats. The esophagus was cannulated and perfused with either 0.1 M PBS or 0.1 N HCl at 1 ml/min as the following parameters were quantified in separate experiments: diameter of bronchi (n = 5), tracheal mucociliary transport rate (n = 4), tracheobronchial mucus secretion (n = 7), and lung function (n = 6). We found that esophageal acidification for 10-30 min decreased bronchial diameters primarily of the smaller low-resistance airways (10-22%, P < 0.05), decreased tracheal mucociliary transport (53%, 8.7 +/- 2.4 vs. 4.1 +/- 1.3 mm/min, P < 0.05), increased tracheobronchial mucus secretion (147%, 3.4 +/- 0.7 vs. 8.4 +/- 2.6 mg/10 min, P < 0.05), and caused no change in total lung resistance or dynamic compliance (P > 0.05). Considering that tracheal mucociliary transport rate is governed in part by mucus secretion, we concluded that the primary airway response to esophageal acidification observed is increased mucus secretion. Airway constriction may act to assist in rapid secretion of mucus and to increase the effectiveness of coughing while not affecting lung resistance or compliance. Given the buffering capabilities of mucus, esophageal acidification activates appropriate physiological responses that may act to neutralize gastroesophageal reflux that reaches the larynx, pharynx, or lower airways.     

Development of a computational fluid dynamics model for mucociliary clearance in the nasal cavity

Intranasal drug delivery has attracted significant attention because of the opportunity to deliver systemic drugs directly to the blood stream. However, the mucociliary clearance poses a challenge in gaining high efficacy of intranasal drug delivery because cilia continuously carry the mucus blanket towards the laryngeal region. To better understand mucus flow behaviour on the human nasal cavity wall, we present computational model development, and evaluation of mucus motion on a realistic nasal cavity model reconstructed from CT-scans. The model development involved two approaches based on the actual nasal cavity geometry namely: (i) unwrapped-surface model in 2D domain and (ii) 3D-shell model. Conservation equations of fluid motion were applied to the domains, where a mucus production source term was used to initiate the mucus motion. The analysis included mucus flow patterns, virtual saccharin tests and quantitative velocity magnitude analysis, which demonstrated that the 3D-shell model results provided better agreement with experimental data. The unwrapped-surface model also suffered from mesh-deformations during the unwrapping stage and this led to higher mucus velocity compared to experimental data. Therefore, the 3D-shell model was recommended for future mucus flow simulations. As a first step towards mucus motion modelling this study provides important information that accurately simulates a mucus velocity field on a human nasal cavity wall, for assessment of toxicology and efficacy of intranasal drug delivery.