Correlation between rheologic properties and in vitro ciliary transport of rat nasal mucus

BPIFB1 loss alters airway mucus properties and diminishes mucociliary clearance

Airway mucociliary clearance (MCC) is required for host defense and is often diminished in chronic lung diseases. Effective clearance depends upon coordinated actions of the airway epithelium and a mobile mucus layer. Dysregulation of the primary secreted airway mucin proteins, MUC5B and MUC5AC, is associated with a reduction in the rate of MCC; however, how other secreted proteins impact the integrity of the mucus layer and MCC remains unclear. We previously identified the gene Bpifb1/Lplunc1 as a regulator of airway MUC5B protein levels using genetic approaches. Here, we show that BPIFB1 is required for effective MCC in vivo using Bpifb1 knockout (KO) mice. Reduced MCC in Bpifb1 KO mice occurred in the absence of defects in epithelial ion transport or reduced ciliary beat frequency. Loss of BPIFB1 in vivo and in vitro altered biophysical and biochemical properties of mucus that have been previously linked to impaired MCC. Finally, we detected colocalization of BPIFB1 and MUC5B in secretory granules in mice and the protein mesh of secreted mucus in human airway epithelia cultures. Collectively, our findings demonstrate that BPIFB1 is an important component of the mucociliary apparatus in mice and a key component of the mucus protein network.NEW & NOTEWORTHY BPIFB1, also known as LPLUNC1, was found to regulate mucociliary clearance (MCC), a key aspect of host defense in the airway. Loss of this protein was also associated with altered biophysical and biochemical properties of mucus that have been previously linked to impaired MCC.

Challenges in the Development and Application of Organ-on-Chips for Intranasal Drug Delivery Studies

With the growing demand for the development of intranasal (IN) products, such as nasal vaccines, which has been especially highlighted during the COVID-19 pandemic, the lack of novel technologies to accurately test the safety and effectiveness of IN products in vitro so that they can be delivered promptly to the market is critically acknowledged. There have been attempts to manufacture anatomically relevant 3D replicas of the human nasal cavity for in vitro IN drug tests, and a couple of organ-on-chip (OoC) models, which mimic some key features of the nasal mucosa, have been proposed. However, these models are still in their infancy, and have not completely recapitulated the critical characteristics of the human nasal mucosa, including its biological interactions with other organs, to provide a reliable platform for preclinical IN drug tests. While the promising potential of OoCs for drug testing and development is being extensively investigated in recent research, the applicability of this technology for IN drug tests has barely been explored. This review aims to highlight the importance of using OoC models for in vitro IN drug tests and their potential applications in IN drug development by covering the background information on the wide usage of IN drugs and their common side effects where some classical examples of each area are pointed out. Specifically, this review focuses on the major challenges of developing advanced OoC technology and discusses the need to mimic the physiological and anatomical features of the nasal cavity and nasal mucosa, the performance of relevant drug safety assays, as well as the fabrication and operational aspects, with the ultimate goal to highlight the much-needed consensus, to converge the effort of the research community in this area of work.

Does Maras powder affect the nasal mucociliary clearence?

PURPOSE

Many studies have been conducted about the effect of cigarettes and other tobacco products on mucociliary clearance. However, there has been no study of the relationship between mucociliary clearance and Maras powder, which is a smokeless tobacco product. The aim of this study was to evaluate the effect of Maras powder use on mucociliary clearance through comparisons with cigarette smokers and those who used no tobacco products.

METHODS

The study included 75 male volunteers, aged 23-54 years. Group 1 (n: 25) comprised subjects who do not use any tobacco products, Group 2 (n: 25) those who smoked cigarettes, and Group 3 (n: 25) those who used Maraş powder. The saccharin test was used to evaluate mucociliary clearance and the time was recorded in seconds. The groups were statistically compared in respect of mean age and mucociliary clearance time (MCCT).

RESULTS

The mean MCCT was determined to be 645.8 ± 200 secs for the whole study sample, 497 ± 108 secs for Group 1, 796 ± 200 secs for Group 2, and 644 ± 161 secs for Group 3. The difference between the groups in respect of MCCT was statistically significant (p < 0.001). No statistically significant difference was determined between the groups in respect of mean age (p = 0.730).

CONCLUSION

The study results demonstrated that the nasal mucociliary clearance time was prolonged both by cigarettes and by the use of Maras powder, and that this time was prolonged more by cigarette smoking than the use of Maras powder.

Engineered modular microphysiological models of the human airway clearance phenomena

Mucociliary clearance is a crucial mechanism that supports the elimination of inhaled particles, bacteria, pollution, and hazardous agents from the human airways, and it also limits the diffusion of aerosolized drugs into the airway epithelium. In spite of its relevance, few in vitro models sufficiently address the cumulative effect of the steric and interactive barrier function of mucus on the one hand, and the dynamic mucus transport imposed by ciliary mucus propulsion on the other hand. Here, ad hoc mucus models of physiological and pathological mucus are combined with magnetic artificial cilia to model mucociliary transport in both physiological and pathological states. The modular concept adopted in this study enables the development of mucociliary clearance models with high versatility since these can be easily modified to reproduce phenomena characteristic of healthy and diseased human airways while allowing to determine the effect of each parameter and/or structure separately on the overall mucociliary transport. These modular airway models can be available off-the-shelf because they are exclusively made of readily available materials, thus ensuring reproducibility across different laboratories.

A 3D-printed microfluidic platform for simulating the effects of CPAP on the nasal epithelium

Obstructive sleep apnoea (OSA) is a chronic disorder that involves a decrease or complete cessation of airflow during sleep. It occurs when the muscles supporting the soft tissues in the throat relax during sleep, causing narrowing or closure of the upper airway. Sleep apnoea is a serious medical condition with an increased risk of cardiovascular complications and impaired quality of life. Continuous positive airway pressure (CPAP) is the most effective treatment for moderate to severe cases of OSA and is effective in mild sleep apnoea. However, CPAP therapy is associated with the development of several nasal side effects and is inconvenient for the user, leading to low compliance rates. The effects of CPAP treatment on the upper respiratory system, as well as the pathogenesis of side effects, are incompletely understood and not adequately researched. To better understand the effects of CPAP treatment on the upper respiratory system, we developed an in vitro 3D-printed microfluidic platform. A nasal epithelial cell line, RPMI 2650, was then exposed to certain conditions to mimic the in-vivo environment. To create these conditions, the microfluidic device was utilized to expose nasal epithelial cells grown and differentiated at the air-liquid interface. The airflow was similar to what is experienced with CPAP, with pressure ranging between 0-20 cm of H20. Cells exposed to pressure showed decreased barrier integrity, change in cellular shape, and increased cell death (lactate dehydrogenase release into media) compared to unstressed cells. Stressed cells also showed increased secretions of inflammatory markers IL-6 and IL-8 and had increased production of ATP. Our results suggest that stress induced by airflow leads to structural, metabolic, and inflammatory changes in the nasal epithelium, which may be responsible for developing nasal side-effects following CPAP treatment.

Active microrheology determines scale-dependent material properties of Chaetopterus mucus

We characterize the lengthscale-dependent rheological properties of mucus from the ubiquitous Chaetopterus marine worm. We use optically trapped probes (2-10 μm) to induce microscopic strains and measure the stress response as a function of oscillation amplitude. Our results show that viscoelastic properties are highly dependent on strain scale (l), indicating three distinct lengthscale-dependent regimes at l1 ≤4 μm, l2≈4-10 μm, and l3≥10 μm. While mucus response is similar to water for l1, suggesting that probes rarely contact the mucus mesh, the response for l2 is distinctly more viscous and independent of probe size, indicative of continuum mechanics. Only for l3 does the response match the macroscopic elasticity, likely due to additional stiffer constraints that strongly resist probe displacement. Our results suggest that, rather than a single lengthscale governing crossover from viscous to elastic, mucus responds as a hierarchical network with a loose biopolymer mesh coupled to a larger scaffold responsible for macroscopic gel-like mechanics.

In vitro mucus transportability, cytogenotoxicity, and hematological changes as non-destructive physiological biomarkers in fish chronically exposed to metals

The biomonitoring of fish using biomarkers represents a useful tool for the assessment of aquatic pollution. This study evaluated the sublethal toxic effects of aquatic pollution on fish collected from a site contaminated by metals. Water and fish (Oreochromis niloticus) samples were collected from a pond in the Parque Ecológico do Tietê (PET) that lies along the Tietê River (São Paulo, Brazil), and from a control site (an experimental fish farm). The metal content of the water was evaluated, and fish were used to examine the properties of gill mucus and blood. The PET fish were evaluated for alterations in the in vitro transportability of mucus and changes in blood properties (e.g., cell volume, hemoglobin concentration, red blood cells, and white blood cell count). The results of the water analyzes indicated metal levels above the legal standards for Fe (0.71 mg/L), Ni (0.06 mg/L), Mn (0.11 mg/L), and Pb (0.48 mg/L). Compared to the controls, the hematologic parameter analyzes of PET fish revealed significantly higher numbers of erythrocytes (RBC), leukocytes (WBC), lymphocytes, erythroblasts, and Mean Corpuscular Volume (MCV); however, the hemoglobin content and Mean Corpuscular Hemoglobin Concentration (MCHC) values were significantly lower. The frequencies of nuclear abnormalities and micronuclei were significantly higher and the mucociliary transport was significantly lower in PET fish than in the controls. These results suggest that fish from the contaminated site exhibit a series of physiological responses, which probably indicate health disturbances. Furthermore, the results suggest that blood and mucus are promising, non-destructive targets for use in the monitoring of pollution.

How does parental smoking affect nasal mucociliary clearance in children?

Correlation between passive smoking and nasal mucociliary clearance (MCC) in pediatric population has not been reported before. Therefore, in this study, we aimed to investigate the relationship between environmental tobacco smoke and nasal MCC in children whose parents smoke in or outside the house. Three groups of subjects were evaluated: control group (group 1) with 18 children who were not exposed to environmental smoke, 15 passive smokers living with at least one adult household member smoking outside the house (group 2), 17 passive smokers living with at least one adult household member smoking inside the house (group 3). Parents of children were asked to answer our questions regarding their smoking history, and nasal MCC time was assessed for all individuals of the 3 groups. The mean MCC value in control group, group 2 and group 3 were 7.33 ± 2.91, 10.00 ± 4.78 and 12.41 ± 3.44, respectively. Differences between the mean nasal MCC values of the groups were statistically significant (p < 0.01). The comparison of MCC values between control group and group 2 did not reveal significant difference, but since p value was very close to significance level, in larger series it could be significant. (p = 0.067). Also, when we compared the MCC values between group 2 and group 3, there was no significant difference (p = 0.173). But, the difference between MCC values of control group and group 3 was statistically significant (p < 0.001). Parental smoking both inside or outside the house seemed to increase nasal mucociliary clearance time when they are compared with healthy controls. Further studies with larger study groups also measuring direct quantitative doses of smoking are needed to verify this important issue.

Functional short- and long-term effects of nasal CPAP with and without humidification on the ciliary function of the nasal respiratory epithelium

PURPOSE

Continuous positive airway pressure (CPAP) is the gold standard in the treatment of obstructive sleep apnea (OSA), but its impact on ciliary function is unclear to date. Furthermore, CPAP is associated with numerous side effects related to the nose and upper airway. Humidified CPAP is used to relieve these symptoms, but again, little is known regarding its effect on ciliary function of the nasal respiratory epithelium.

METHODS

In this prospective, randomized, crossover trial, 31 patients with OSA (AHI >15/h) were randomized to two treatment arms: nasal continuous positive airway pressure (nCPAP) with humidification or nCPAP without humidification for one night in each modality to assess short-term effects of ciliary beat frequency (CBF) and mucus transport time (MTT) and consecutively for 8 weeks in each modality to assess long-term effects in a crossover fashion.

RESULTS

The baseline CBF was 4.8 ± 0.6 Hz, and baseline MTT was 540 ± 221 s. After one night of CPAP with and without humidification, ciliary function increased moderately yet with statistical significance (p <0.05). The short-term groups with and without humidification did not differ statistically significant. Regarding long-term effects of CPAP, a statistically significant increase in ciliary function above the baseline level and above the short-term level was shown without humidification (7.2 ± 0.4 Hz; 402 ± 176 s; p <0.01). The increase above baseline level was even more pronounced with humidification (9.3 ± 0.7 Hz; 313 ± 95 s; p <0.01). There was a statistically significant difference between both groups at long-term assessment with regard to CBF (p <0.01).

CONCLUSIONS

Independent of airway humidification, nCPAP has moderate effects on short-term ciliary function of the nasal respiratory epithelium. However, a significant increase in ciliary function-both in terms of an increased CBF and a decreased MTT-was detected after long-term use. The effect was more pronounced when humidification was used during nCPAP.

The effects of CPAP treatment on nasal mucosa in patients with obstructive sleep apnea

The aim of the study was to demonstrate the effects of nasal CPAP treatment on the morphology and function of nasal mucosa in patients with obstructive sleep apnea (OSA). Patients with complaints relevant to OSA underwent respiratory function tests, arterial blood gas analyses and polysomnography. Saccharine test and nasal biopsies were performed to assess the mucociliary transport time and to observe the histopathological changes in patients with apnea-hypopnea index ≥15 in whole night polysomnography. Tissue samples were obtained from middle and inferior turbinates and septal mucosa to observe the degree of inflammation and fibrosis by semiquantitative means. Biopsies and mucociliary transport test were performed before and 3 months after the initiation of CPAP treatment. A total of 25 patients with a mean age of 52 were enrolled in the study. While the pretreatment mucociliary transport time before and 3 months after the treatment were 10.50 and 11.50 min respectively. The difference between these values was statistically insignificant. Mean apnea-hypopnea index was 63.19, while mean partial oxygen pressure was 75.46 mmHg. Nasal CPAP treatment was introduced with a mean pressure of 9.54 cmH2O. The degree of inflammation and fibrosis was found to be significantly increased after CPAP treatment. Nasal CPAP leads to alterations in mucosa. Efforts should be directed to make CPAP treatment a safer method via protecting the morphologic and functional properties of the nasal mucosa.

Effects of biomass burning on nasal mucociliary clearance and mucus properties after sugarcane harvesting

OBJECTIVE

Biofuel from sugarcane is widely produced in developing countries and is a clean and renewable alternative source of energy. However, sugarcane harvesting is mostly performed after biomass burning. The aim of this study was to evaluate the effects of harvesting after biomass burning on nasal mucociliary clearance and the nasal mucus properties of farm workers.

METHODS

Twenty seven sugarcane workers (21-45 years old) were evaluated at the end of two successive time-periods: first at the end of a 6-month harvesting period (harvesting), and then at the end of a 3-month period without harvesting (non-harvesting). Nasal mucociliary clearance was evaluated by the saccharine transit test, and mucus properties were analyzed using in vitro mucus contact angle and mucus transportability by sneeze. Arterial blood pressure, heart rate, respiratory rate, pulse oximetry, body temperature, associated illness, and exhaled carbon monoxide were registered.

RESULTS

Data are presented as mean values (95% confidence interval). The multivariate model analysis adjusted for age, body-mass index, smoking status and years of working with this agricultural practice showed that harvesting yielded prolonged saccharine transit test in 7.83 min (1.88-13.78), increased mucus contact angle in 8.68 degrees (3.18-14.17) and decreased transportability by sneeze in 32.12 mm (-44.83 to -19.42) compared with the non-harvesting period. No significant differences were detected in any of the clinical parameter at either time-period.

CONCLUSION

Sugarcane harvesting after biomass burning negatively affects the first barrier of the respiratory system in farm workers by impairing nasal mucociliary clearance and inducing abnormal mucus properties.

Model of ciliary clearance and the role of mucus rheology

It has been observed that the transportability of mucus by cilial mats is dependent on the rheological properties of the mucus. Mucus is a non-Newtonian fluid that exhibits a plethora of phenomena such as stress relaxation, tensile stresses, shear thinning, and yielding behavior. These observations motivate the analysis in this paper that considers the first two attributes in order to construct a transport model. The model developed here assumes that the mucus is transported as a rigid body, the metachronal wave exhibits symplectic behavior, that the mucus is thin compared to the metachronal wavelength, and that the effects of individual cilia can be lumped together to impart an average strain to the mucus during contact. This strain invokes a stress in the mucus, whose non-Newtonian rheology creates tensile forces that persist into unsheared regions and allow the unsupported mucus to move as a rigid body whereas a Newtonian fluid would retrograde. This work focuses primarily on the Doi-Edwards model but results are generalized to the Jeffrey's and Maxwell fluids as well. The model predicts that there exists an optimal mucus rheology that maximizes the shear stress imparted to the mucus by the cilia for a given cilia motion. We propose that this is the rheology that the body strives for in order to minimize energy consumption. Predicted optimal rheologies are consistent with results from previous experimental studies when reasonable model parameters are chosen.

Micro- and macrorheology of mucus

Mucus is a complex biological material that lubricates and protects the human lungs, gastrointestinal (GI) tract, vagina, eyes, and other moist mucosal surfaces. Mucus serves as a physical barrier against foreign particles, including toxins, pathogens, and environmental ultrafine particles, while allowing rapid passage of selected gases, ions, nutrients, and many proteins. Its selective barrier properties are precisely regulated at the biochemical level across vastly different length scales. At the macroscale, mucus behaves as a non-Newtonian gel, distinguished from classical solids and liquids by its response to shear rate and shear stress, while, at the nanoscale, it behaves as a low viscosity fluid. Advances in the rheological characterization of mucus from the macroscopic to nanoscopic levels have contributed critical understanding to mucus physiology, disease pathology, and the development of drug delivery systems designed for use at mucosal surfaces. This article reviews the biochemistry that governs mucus rheology, the macro- and microrheology of human and laboratory animal mucus, rheological techniques applied to mucus, and the importance of an improved understanding of the physical properties of mucus to advancing the field of drug and gene delivery.

Analysis of the sputum and inflammatory alterations of the airways in patients with common variable immunodeficiency and bronchiectasis

INTRODUCTION

Common variable immunodeficiency is characterized by defective antibody production and recurrent pulmonary infections. Intravenous immunoglobulin is the treatment of choice, but the effects of Intravenous immunoglobulin on pulmonary defense mechanisms are poorly understood.

OBJECTIVE

The aim of this study was to verify the impact of intravenous immunoglobulin on the physical properties of the sputum and on inflammatory alterations in the airways of patients with Common variable immunodeficiency associated with bronchiectasis.

METHOD

The present study analyzed sputum physical properties, exhaled NO, inflammatory cells in the sputum, and IG titers in 7 patients with Common variable immunodeficiency and bronchiectasis with secretion, immediately before and 15 days after Intravenous immunoglobulin. A group of 6 patients with Common variable immunodeficiency and bronchiectasis but no sputum was also studied for comparison of the basal IgG level and blood count. The 13 patients were young (age=36+/-17 years) and comprised predominantly of females (n=11).

RESULTS

Patients with secretion presented significantly decreased IgG and IgM levels. Intravenous immunoglobulin was associated with a significant decrease in exhaled NO (54.7 vs. 40.1 ppb, p<0.05), sputum inflammatory cell counts (28.7 vs. 14.6 cells/mm(3), p<0.05), and a significant increase in respiratory mucus transportability by cough (42.5 vs. 65.0 mm, p < 0.05).

CONCLUSION

We concluded that immunoglobulin administration in Common variable immunodeficiency patients results in significant improvement in indexes of inflammation of the airways with improvement in the transportability of the respiratory mucus by cough.

Methods for studying mucociliary transport

Mucociliary transport dysfunctions can impair the quality of life of patients suffering from chronic rhinossinusitis and lead to severe consequences such as alterations in respiratory physiology or even death as in cases of cystic fibrosis and primary ciliary dyskinesia. Therefore, it is crucial to understand the physiology of the mucociliary apparatus and how its components (cilia, mucus-periciliary layer and its interaction) affect the clearance of respiratory secretions. Aims: This paper aims to review and to discuss different techniques for studying mucociliary transport and their clinical and experimental applicability. Conclusions: The methods listed in this revision provide us with valuable information about different aspects of the mucociliary transport. Some of the methods listed are more suitable for clinical practice and present reproducible results. Others, show only applicability in experimental settings due to technical difficulties or financial limitations. However, it is important to emphasize that up to now there is no method that can evaluate ciliary beating frequency (CBF) in vivo and in situ. Such a method would become a valuable tool in the scientific scenario and in the clinical practice, supporting the diagnosis of ciliary dyskinesias and avoiding the use of invasive procedures to corroborate the clinical suspicion

Nasal mucus transportability in children with cleft palate

OBJECTIVES

Children with cleft palate (CP) have a high prevalence of sinusitis. Considering that nasal mucus properties play a pivotal role in the upper airway defense mechanism, the aim of the study was to evaluate nasal mucus transportability and physical properties from children with CP.

SETTING

Hospital for Rehabilitation of Craniofacial Anomalies, School of Dentistry, University of São Paulo, Bauru, SP, Brazil and Laboratory of Experimental Air Pollution, School of Medicine, University of São Paulo, São Paulo, SP, Brazil.

METHODS

Nasal mucus samples were collected by nasal aspiration from children with CP and without CP (non-CP). Sneeze clearance (SC) was evaluated by the simulated sneeze machine. In vitro mucus transportability (MCT) by cilia was evaluated by the frog palate preparation. Mucus physical surface properties were assessed by measuring the contact angle (CA). Mucus rheology was determined by means of a magnetic rheometer, and the results were expressed as log G* (vectorial sum of viscosity and elasticity) and tan delta (relationship between viscosity and elasticity) measured at 1 and 100 rad/s.

RESULTS

Mucus samples from children with CP had a higher SC than non-CP children (67+/-30 and 41+/-24 mm, respectively, p<0.05). Mucus samples from children with CP had a lower CA (24+/-16 degrees and 35+/-11 degrees , p<0.05) and a higher tan delta 100 (0.79+/-0.24 and 0.51+/-0.12, p<0.05) than non-CP children. There were no significant differences in mucus MCT, log G* 1, tan delta 1 and log G* 100 obtained for CP and non-CP children.

CONCLUSIONS

Nasal mucus physical properties from children with CP are associated with higher sneeze transportability. The high prevalence of sinusitis in children with CP cannot be explained by changes in mucus physical properties and transportability.

Métodos de estudo do transporte mucociliar

Disfunções no transporte mucociliar trazem desde queda na qualidade de vida dos pacientes, como nas rinites e rinossinusites crônicas, até graves conseqüências com risco de seqüelas irreversíveis e mesmo letais, como nos casos de fibrose cística e das discinesias ciliares primárias. Desta forma, torna-se fundamental o conhecimento do funcionamento normal do aparelho mucociliar e de como alterações em seus componentes (cílio, muco-fluido periciliar e interação dinâmica entre ambos) afetam o transporte das secreções respiratórias. OBJETIVOS: Este artigo visa a revisar e discutir as diferentes técnicas de avaliação do transporte mucociliar descrevendo suas peculiaridades e aplicabilidades clínicas e experimentais. CONCLUSÕES: Os métodos citados nesta revisão nos fornecem informações importantes sobre os diferentes aspectos do transporte mucociliar. Alguns apresentam uma maior facilidade de realização e resultados reprodutíveis, já outros apenas mostraram-se com aplicabilidade em protocolos de pesquisa em virtude de dificuldades técnicas e limitações financeiras. Há que se considerar a inexistência de métodos que avaliem ambulatorialmente a freqüência de batimento ciliar (FBC) "in vivo" e "in situ", o que se tornaria uma ferramenta importante, tanto no âmbito científico, quanto na prática clínica, auxiliando no diagnóstico das discinesias ciliares e evitando a realização de procedimentos mais invasivos para a sua confirmação diagnóstica.

Cyclosporin A reduces airway mucus secretion and mucociliary clearance in rats

PURPOSE

To assay the effects of cyclosporin A on mucus secretion from goblet cells and on mucociliary transport in situ in rats.

METHODS

Twenty-one male Wistar rats were assigned to 3 groups: control (n = 5), saline (n = 8), and cyclosporin A (n = 8). After 30 days of drug therapy, the rats were killed, and the lungs were removed from the thoracic cavity. Mucus samples were collected, and the transport rate was evaluated in vitro using a bullfrog palate model. Mucociliary transport was timed in situ by direct view of particles trapped on the mucus moving across the respiratory tract. Finally, the amount of stored mucins in the goblet cells of the respiratory epithelium was measured.

RESULTS

Drug dosage measurements showed that cyclosporine blood concentration at the moment the rats were killed was 1246.57 +/- 563.88 ng/mL. The in vitro transport rate was significantly lower (P < .001) in the cyclosporin A-treated group. Also, the in-situ mucociliary transport rate was decreased in all cyclosporin A-treated animals when compared to the saline group (P = .02). Mucus quantity measurements showed a significant decrease on both acid (P = .01) and neutral (P = .02) mucus production from goblet cells in the animals submitted to cyclosporin A therapy. The correlation between the percentage of total mucus and in vitro transport rate was positive and significant (r = 0.706, P < .001), as was the correlation between the percentage of total mucus and the in situ mucociliary transport rate (r = 0.688, P = .001).

CONCLUSION

This study shows that cyclosporin A plays an important role in the impairment of the mucociliary clearance in rats by reducing both acid and neutral mucus production from goblet cells and causing a decrease in the mucociliary transport velocity.

Formulating gels for decreased mucociliary transport using rheologic properties: polyacrylic acids

The purpose of these studies was to identify the rheologic properties of polyacrylic acid gels necessary for optimal reductions in mucociliary clearance. The mucociliary transport of 2 bioadhesive polyacrylic acid polymers, polycarbophil and carbopol, was assessed in vitro by measuring their clearance rates across explants of ciliated bovine tracheal tissue. The viscoelastic properties of polymer gels were measured in the presence of mucus using controlled stress rheometry. Combinations of apparent viscosity (eta) and complex modulus (G*) were found to be the most useful parameters in the identification of polyacrylic acid formulations capable of decreasing mucociliary transport rate (MTR). A narrow range of eta and G* values suitable for reducing mucociliary clearance, while remaining sufficiently fluid for intranasal administration, were identified. The correlations between the rheologic parameters of the polycarbophil gels and their mucociliary transport rates were used to identify other polyacrylic acid gels that also had suitable mucociliary clearance properties, demonstrating that these parameters can be used to direct the optimization of formulations using simple in vitro rheologic testing.

Rheological characterization of neutral and anionic polysaccharides with reduced mucociliary transport rates

The purpose of this research was to compare the viscoelastic properties of several neutral and anionic polysaccharide polymers with their mucociliary transport rates (MTR) across explants of ciliated bovine tracheal tissue to identify rheologic parameters capable of predicting the extent of reduction in mucociliary transport. The viscoelastic properties of the polymer gels and gels mixed with mucus were quantified using controlled stress rheometry. In general, the anionic polysaccharides were more efficient at decreasing the mucociliary transport rate than were the neutral polymers, and a concentration threshold, where no further decreases in mucociliary transport occurred with increasing polymer concentration, was observed for several of the neutral polysaccharides. No single rheologic parameter (eta, G', G'', tan delta, G*) was a good predictor of the extent of mucociliary transport reduction, but a combination of the apparent viscosity (eta), tangent to the phase angle (tan delta), and complex modulus (G*) was found to be useful in the identification of formulations capable of decreasing MTR. The relative values of each of the rheologic parameters were unique for each polymer, yet once the relationships between the rheologic parameters and mucociliary transport rate reduction were determined, formulations capable of resisting mucociliary clearance could be rapidly optimized.

Photoacoustic monitoring of the absorption of isotonic saline solution by human mucus

Viscosity and elasticity are the fundamental rheologic properties of respiratory mucus, and are important determinants of transportability of mucus in the mucociliary system. One technique that permits to monitor indirectly the rheologic properties of any sample is the photoacoustic technique. Using that technique, the absorption of isotonic saline solution by human mucus was monitored. The mucus was obtained from 11 volunteers, divided into two groups: five volunteers presenting pneumology symptoms (group I) and six healthy volunteers (group II). The photoacoustic signal of the mucus absorbing the saline solution was monitored as function of time, with measurements being performed each 10 min, up to 120 min. The resulting curves were fitted to sigmoidal curves to simulate the evolution on time of the photoacoustic signal. A characteristic time for the half saturation of the absorption process was obtained. For group I the time obtained was 23.3+/-5.3 min and for group II the time obtained was 55.0+/-7.7 min, both means being significantly different (Student t-test, p<0.05). This result supports the empirical practice of treating individuals presenting symptoms of airway obstruction with about 30 min of inhalations of isotonic saline solution vapor for the clearance of the airways.

Short-term effects of nCPAP on nasal mucociliary clearance and mucus transportability in healthy subjects

Nasal mucociliary clearance is a primary defense mechanism of the upper airways and may be acutely affected by nasal continuous positive airway pressure (nCPAP). nCPAP treatment is effective and safe. However, it can cause nasal side effects and contribute to a low compliance to the treatment. The aim of this study was to investigate the short-term effects of nCPAP on nasal mucociliary clearance and on mucus transportability of healthy subjects. Eleven healthy subjects were submitted to 20 min of nCPAP (10 cm H2O). Five subjects were also evaluated before and after 20 min of rest on the consecutive study day. Nasal mucociliary clearance was measured by the saccharin nasal transit time test and nasal mucus was collected for the in vitro study of mucus transportability by the frog palate model, both before and after the nCPAP challenge. Saccharin nasal transit time decreased significantly after nCPAP (9.29+/-6.06 min and 4.83+/-5.57 min; P=0.002 before and after nCPAP respectively). No significant changes were observed on the control day (11.66+/-7.57 min and 12.40+/-5.62 min; P=0.70). Mucus transportability was not significantly affected by nCPAP. Our results suggest that nCPAP can acutely increase nasal mucociliary clearance but does not affect in vitro mucus transportability in healthy subjects.

Mucociliary clearance is impaired in acutely ill patients

OBJECTIVE

This study aimed to investigate nasal mucociliary clearance in acutely ill patients who were clinically stable and had no airway manipulation.

DESIGN

Prospective clinical study.

SETTING

Medical ICU.

PATIENTS AND PARTICIPANTS

Sixteen medical patients admitted to the ICU and 16 healthy subjects were studied. Patients who were receiving airway manipulation, including tracheal suctioning, nasogastric or enteral tubes, noninvasive and invasive mechanical ventilation, were excluded.

INTERVENTIONS

Mucociliary clearance was evaluated by saccharine transit time (STT) measurements at ICU admission (admission) and 90 days after hospital discharge (recovery). Healthy subjects were also subjected to two measurements 90 days apart.

MEASUREMENTS AND RESULTS

The STT of patients was 26.4 +/- 11.3 min and 17.9 +/- 8.6 min at admission and recovery (p = 0.002) [mean +/- SD] but did not change along the 90-day interval in healthy subjects (17.2 +/- 10.2 min and 16.7 +/- 10.3 min), respectively. Smokers (patients and healthy subjects) presented prolonged STT when compared to nonsmokers (p = 0.026). STT at admission correlated positively with heart rate (r = 0.560; p = 0.024) and hospital stay (r = 0.634; p = 0.008).

CONCLUSION

Mucociliary clearance is impaired in stable acutely ill patients with no airway manipulation and correlates with simple markers of underlying disease severity. Mucociliary dysfunction may help to explain the increased susceptibility of hospital-acquired respiratory infection in critically ill patients.

Sputum induction as a research tool for the study of human respiratory mucus

The study objectives were to compare in vitro transportability and physical properties of respiratory mucus, obtained invasively by direct collection (DC) right after endotracheal intubation and non-invasively by sputum induction with 3% hypertonic saline solution inhalation (SI) 24 h before the anesthesia. Twenty-two patients with no pulmonary disease scheduled for elective abdominal surgical procedures were studied. The parameters analyzed and the main results are as follows. (1) Transportability by cilia (MCT), SI was higher than DC (0.94+/-0.25 and 0.62+/-0.25; P<0.001). There was a significant correlation between the two methods and DC could be estimated by: DC=0.21+(0.44 SI) (r=0.44; P<0.001). (2) Transportability by cough (CC), SI was higher than DC (68.23+/-32.1 and 33.58+/-19.04 mm; P=0.002). (3) Contact angle (CA), SI was lower than DC (10+/-3 degrees and 22+/-14 degrees ; P=0.025). (4) Rheological properties (no significant difference obtained between SI and DC). These results indicated that SI changes mucus physical properties and transportability in non-expectorators.

Respiratory fluid mechanics and transport processes

The field of respiratory flow and transport has experienced significant research activity over the past several years. Important contributions to the knowledge base come from pulmonary and critical care medicine, surgery, physiology, environmental health sciences, biophysics, and engineering. Several disciplines within engineering have strong and historical ties to respiration including mechanical, chemical, civil/environmental, aerospace and, of course, biomedical engineering. This review draws from a wide variety of scientific literature that reflects the diverse constituency and audience that respiratory science has developed. The subject areas covered include nasal flow and transport, airway gas flow, alternative modes of ventilation, nonrespiratory gas transport, aerosol transport, airway stability, mucus transport, pulmonary acoustics, surfactant dynamics and delivery, and pleural liquid flow. Within each area are a number of subtopics whose exploration can provide the opportunity of both depth and breadth for the interested reader.

Effects of intravenous furosemide on mucociliary transport and rheological properties of patients under mechanical ventilation

The use of intravenous (IV) furosemide is common practice in patients under mechanical ventilation (MV), but its effects on respiratory mucus are largely unknown. Furosemide can affect respiratory mucus either directly through inhibition of the NaK(Cl)2 co-transporter on the basolateral surface of airway epithelium or indirectly through increased diuresis and dehydration. We investigated the physical properties and transportability of respiratory mucus obtained from 26 patients under MV distributed in two groups, furosemide (n = 12) and control (n = 14). Mucus collection was done at 0, 1, 2, 3 and 4 hours. The rheological properties of mucus were studied with a microrheometer, and in vitro mucociliary transport (MCT) (frog palate), contact angle (CA) and cough clearance (CC) (simulated cough machine) were measured. After the administration of furosemide, MCT decreased by 17 +/- 19%, 24 +/- 11%, 18 +/- 16% and 18 +/- 13% at 1, 2, 3 and 4 hours respectively, P < 0.001 compared with control. In contrast, no significant changes were observed in the control group. The remaining parameters did not change significantly in either group. Our results support the hypothesis that IV furosemide might acutely impair MCT in patients under MV.

Effects of formaldehyde on the frog's mucociliary epithelium as a surrogate to evaluate air pollution effects on the respiratory epithelium

The increasing use of alcohol as an alternative fuel to gasoline or diesel can increase emission of formaldehyde, an organic gas that is irritant to the mucous membranes. The respiratory system is the major target of air pollutants and its major defense mechanism depends on the continuous activity of the cilia and the resulting constant transportation of mucous secretion. The present study was designed to evaluate the effects of formaldehyde on the ciliated epithelium through a relative large dose range around the threshold limit value adopted by the Brazilian legislation, namely 1.6 ppm (1.25 to 5 ppm). For this purpose, the isolated frog palate preparation was used as the target of toxic injury. Four groups of frog palates were exposed to diluted Ringer solution (control, N = 8) and formaldehyde diluted in Ringer solution at three different concentrations (1.25, 2.5 and 5.0 ppm, N = 10 for each group). Mucociliary clearance and ciliary beat frequency decreased significantly in contact with formaldehyde at the concentrations of 2.5 and 5.0 ppm after 60 min of exposure (P<0.05). We conclude that relatively low concentrations of formaldehyde, which is even below the Brazilian threshold limit value, are sufficient to cause short-term mucociliary impairment.

Effects of a heat and moisture exchanger and a heated humidifier on respiratory mucus in patients undergoing mechanical ventilation

OBJECTIVE

To evaluate the effects of a heat and moisture exchanger and a heated humidifier on respiratory mucus and transportability by cilia and cough in patients undergoing invasive mechanical ventilation (up to 72 hrs).

DESIGN

Prospective, randomized, clinical study.

SETTING

General intensive care unit and university research laboratory.

PATIENTS

A total of 32 consecutive patients with acute respiratory failure, who were intubated and mechanically ventilated in the intensive care unit setting, were enrolled in the study.

INTERVENTIONS

Patients were randomly assigned to receive as a humidifying system a heat and moisture exchanger (HME) or heated humidified water (HHW) at the onset of mechanical ventilation (time 0). Respiratory mucus samples were collected by suction using a sterile technique at time 0, 24, 48, and 72 hrs of mechanical ventilation.

MEASUREMENTS AND MAIN RESULTS

Eleven patients were excluded from this study because of either extubation or death before 72 hrs of mechanical ventilation, leaving 12 patients in the HME group and nine patients in the HHW group. Ventilatory variables including minute volume, mean airway pressure, positive end-expiratory pressure, Fio2, as well as Pao2/Fio2 ratio, fluid balance (last 6 hrs), furosemide, and inotrope administration (last 4 hrs) were recorded. In vitro mucus transportability by cilia was evaluated on the mucus-depleted frog palate model, and the results were expressed as the mucus transport rate. Cough clearance (an estimation of the interaction between the flow of air and the mucus lining the bronchial walls) was measured using a simulated cough machine, the results being expressed in millimeters. Mucus wettability was measured by the contact angle between a mucus sample drop and a flat glass surface. Mucus rheologic properties (mechanical impedance [log G*] and the ratio between viscosity and elasticity [tan delta]) were measured using a magnetic microrheometer at 1 and 100 cGy/sec deformation frequency. The two humidification groups were comparable in terms of the Acute Physiology and Chronic Health Evaluation II score, age, gender, ventilatory variables, fluid balance, use of inotropes, and furosemide.

CONCLUSION

Ours results indicate that air humidification with either HME or HHW at 32 degrees C (89.6 degrees F) has similar effects on mucus rheologic properties, contact angle, and transportability by cilia in patients undergoing mechanical ventilation, except for transportability by cough, which diminished after 72 hrs of mechanical ventilation in the HME group (p = .0441).

Exogenous surfactant therapy and mucus rheology in chronic obstructive airway diseases

Exogenous surfactant is a specialized biomaterial used for substitution of the lipoprotein mixture normally present in the lungs-pulmonary surfactant. Respiratory Distress Syndrome is a disease of preterm infants mainly caused by pulmonary immaturity as evidenced by a deficiency of mature lung surfactant. Pulmonary surfactant is known to stabilize small alveoli and prevent them from collapsing during expiration. However, apart from alveoli, surfactant also lines the narrow conducting airways of the tracheobronchial tree. This paper reviews the role of this surfactant in the airways and its effect on mucus rheology and mucociliary clearance. Its potential role as a therapeutic biomaterial in chronic obstructive airway diseases, namely asthma, chronic bronchitis, and respiratory manifestations of cystic fibrosis, are discussed. This paper also attempts to elucidate the exact steps in the pathogenic pathway of these diseases which could be reversed by supplementation of exogenous surfactant formulations. It is shown that there is great potential for the use of present day surfactants (which are actually formulated for use in Respiratory Disease Syndrome) as therapy in the aforementioned diseases of altered mucus viscoelasticity and mucociliary clearance. However, for improved effectiveness, specific surfactant formulations satisfying certain specific criteria should be tailor-made for the clinical condition for which they are intended. The properties required to be fulfilled by the optimal exogenous surfactant in each of the above clinical conditions are enumerated in this paper.

Effect of biochemical components on rheologic properties of nasal mucus in chronic sinusitis

The effect of biochemical components on the viscoelasticity of nasal mucus from 24 patients with chronic sinusitis (CS) was investigated by multiple stepwise regression analysis. The dynamic viscosity (eta') and the elastic modulus (G') of nasal mucus were determined with an oscillating sphere magnetic rheometer at oscillatory frequencies of 1 and 10 Hz. The eta' and G' values of mucus determined at 1 Hz were 1.6 +/- 1.5 Pa/s and 31.8 +/- 31.0 Pa, respectively, and these values were much higher than optimal viscoelasticity for mucociliary transport. The concentrations of fucose, N-acetyl neuraminic acid, albumin, IgG, secretory-IgA, and lysozyme were measured in the same mucus samples. The multiple regression analysis showed that the concentration of fucose, a marker of mucous glycoproteins, was the most important determinant of eta' and G'. The analysis also revealed that the level of IgG was the next important determinant. The coefficients of multiple determination for fucose and IgG were 0.732 and 0.733 when the response variables were eta' and G', respectively. The results indicate that locally produced mucous glycoproteins may largely contribute to the high viscoelasticity of nasal mucus in CS.

The use of the frog palate preparation to assess the effects of oxidants on ciliated epithelium

This work was designed to develop a simple method based on the frog palate preparation to study the effects of hydrogen peroxide (H2O2) on ciliated epithelium. For this purpose, five sets (n = 10 per set) of frog palate preparations (Rana catesbeiana) were studied during 35 min after immersion in increasing concentrations of H2O2: 1, 8, 16, 32, and 64 microM. The effects of H2O2 on ciliated epithelium were assessed by measuring transepithelial potential difference (PD) and mucociliary transport (MT). Measurements were performed at 5-min intervals. In addition, the palates submitted to the 64 microM dose were immersed in Ringer's solution and followed by another 30 min to assess the possible recovery after maximal injury. Transepithelial potential difference (PD) was measured by means of agar-filled microelectrodes connected to the high input of a grounded electrometer. Mucociliary transport (MT) was determined by directly monitoring the movement of autologous mucus along the palate surface. Significant decrease in MT was observed in 16 microM and beyond and significant change in PD was observed in 32 microM and 64 microM. Palates submitted to 64 microM of H2O2 returned to their baseline levels of PD and MT within 30 min of recovery in Ringer's solution. In conclusion, the frog palate preparation was shown to be an efficient experimental tool to assess the deleterious effects of H2O2 on the ciliated epithelium.

Nasal mucus clearance in rats: differences with sex and phase of the oestrous cycle

We studied the changes in airway mucus rheology and clearability, as well as in morphometric indices, between male rats and females in either the oestrous or dioestrous phases of the oestrous cycle. Three-month-old Wistar rats were studied and the phases of the oestrous cycle were determined based on analysis of vaginal smears stained by a modified Shorr's procedure. Nasal mucus samples were analysed by means of magnetic rheometry and determination of in vitro transport rate in the frog palate preparation. In situ clearance on the exposed nasal septum was also determined. The mucociliary velocity in situ was significantly affected by both sex and the oestrous cycle phase. In female rats, dioestrous phase clearance was significantly slower than the oestrous phase one. Clearance in male rats was faster than that of both the phases studied in females. Mucus rigidity of females in the oestrous phase was more rigid than that of females in the dioestrous phase and that of males. Mucus viscosity/elasticity ratio for deformations performed at high frequencies was greater for females in comparison with males. Cough clearability computed on the basis of rheological parameters was predicted to be more favourable in females. There were no significant differences between the three groups in mucociliary clearance in vitro. Morphometric studies of the nasal epithelium showed that epithelial and glandular volumes did not exhibit sex- or oestrous-phase-related differences, but the amount of epithelial acidic glycoproteins was lower in females in the oestrous phase in comparison with males and those in the dioestrous phase, the same trend being observed in the glands of the lamina propria.(ABSTRACT TRUNCATED AT 250 WORDS)

Rheological determinants of mucociliary transport in the nose of the rat

The present work was designed to investigate whether the rheological determinants for nasal mucociliary transport are the same in the intact preparation (in situ), as they are when the mucus is added exogenously to the isolated, mucus-depleted frog palate (in vitro). We evaluated the association between estimators of mucociliary transport in both conditions and rheological parameters using multiple regression techniques. Two kinds of rats were used: (a) specific pathogen free (SPF) rats, representing the normal condition of respiratory epithelium; (b) non-SPF rats (NSPF), which have a chronic inflammatory process in the airways. In situ mucociliary clearance (MCC) was determined by measuring the displacement of charcoal particles placed in the nasal septum. In vitro mucociliary transport (MCT) of rat nasal mucus was measured using the isolated frog palate preparation. Mucus rheologic properties were determined by magnetic microrheometry, in oscillatory deformations performed at 1, 10 and 100 radians/sec. No differences were detected between SPF and NSPF rats in terms of rheological parameters. A decreased MCC was found in NSPF in comparison with the SPF group, but no differences were observed between groups in terms of MCT, as could be predicted by rheological data. When all animals were pooled, in situ transport was significantly associated with the viscosity/elasticity ratio, whereas in vitro transport was dependent on the total mechanical impedance of the mucus sample. In conclusion, in situ mucus transport is influenced by other rheological parameters than those associated with in vitro transportability.