The spatial distribution of cystic echinococcosis in Italian ruminant farms from routine surveillance data

Introduction

Cystic echinococcosis (CE) is a zoonotic parasite caused by the cestode Echinococcus granulosus sensu lato (s.l.) which predominantly affects livestock. The disease is endemic in central-southern and insular Italy, with CE particularly infecting sheep, goats, cattle, and water buffalo. The spatial distribution of CE in endemic regions is not widely understood, with surveillance efforts varying across the region.

Methods

In this study, we investigated the spatial distribution of CE in livestock using samples from farms across different livestock species using a Stochastic Partial Differential Equations (SPDE) model. Samples were collected during a survey conducted in the area of central-southern and insular Italy between the years 2019 – 2021.

Results

A total of 3141 animal samples (126 goats, 601 sheep and 2414 cattle and water buffalo) were inspected for Echinococcus s.l. cysts through routine surveillance in abattoirs by postmortem visual examination, palpation and incision of target organs. The geographic location of the farm of origin (a total of 2,878) for each sample was recorded. CE prevalence of 46.0% (1,323/2,878) was estimated at the farm level with 78.3% (462/590) of farms with sheep, 28.6% (36/126) of farms with goats, 36.5% (747/2,049) of farms with cattle, and 23.5% (102/434) of farms with water buffalo infected.

Discussion

The spatial model evaluated the probability of infection in farms across the sampled regions, with the distribution of CE showing high clustering of infected cattle farms in Sardinia and Sicily regions, and sheep farms in Salerno province (Campania region). The output of this study can be used to identify CE hot-spots and to improve surveillance and control programs in endemic areas of Italy.

The economic evaluation of Cystic echinococcosis control strategies focused on zoonotic hosts: A scoping review

Background

Cystic echinococcosis (CE) is a zoonotic neglected tropical disease (zNTD) which imposes considerable financial burden to endemic countries. The 2021–2030 World Health Organization’s roadmap on NTDs has proposed that intensified control be achieved in hyperendemic areas of 17 countries by 2030. Successful interventions for disease control, and the scale-up of programmes applying such interventions, rely on understanding the associated costs and relative return for investment. We conducted a scoping review of existing peer-reviewed literature on economic evaluations of CE control strategies focused on Echinococcus granulosus zoonotic hosts.

Methodology/Principal findings

Database searches of Scopus, PubMed, Web of Science, CABI Direct and JSTOR were conducted and comprehensively reviewed in March 2022, using predefined search criteria with no date, field or language restrictions. A total of 100 papers were initially identified and assessed for eligibility against strict inclusion and exclusion criteria, following the Preferred Reporting Items for Systematic reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR) guidelines. Bibliography review of included manuscripts was used to identify additional literature. Full review of the final manuscript selection (n = 9) was performed and cost data for control interventions were extracted.

Conclusions/Significance

There are very little published data pertaining to the cost and cost effectiveness of CE control interventions targeting its zoonotic hosts. Data given for costs are often incomplete, thus we were unable to perform an economic analysis and cost effectiveness study, highlighting a pressing need for this information. There is much scope for future work in this area. More detailed information and disaggregated costings need to be collected and made available. This would increase the accuracy of any cost-effective analyses to be performed and allow for a greater understanding of the opportunity cost of healthcare decisions and resource allocation by stakeholders and policy makers for effective and cost-effective CE control.

Cystic echinococcosis (CE) is a zoonotic neglected tropical disease which predominantly affects poor pastoral communities globally. The parasite cycles between farm dogs and livestock, and is associated with livestock farming and feeding of infected offal to dogs. Although no noticeable clinical signs are seen in livestock, some production losses, such as reduced milk yield and live weight gain may be observed, and offal condemnation at slaughter is common. The disease can also affect people, due to accidental ingestion of parasite eggs on contaminated food and contact with dogs. Human morbidity and mortality occur due to cyst formation in body organs, exerting a substantial health and financial burden to the health sector of affected countries. Control interventions to reduce CE transmission include sheep vaccination and dog deworming. Long-term control programmes are often expensive, and the true costs of such programmes poorly documented. This scoping review aims to examine published literature on the costs of CE control in zoonotic hosts and report detailed costs of individual elements of a control programme, thereby furthering our understanding of the true economic cost of CE control.

Workshop: tuning the 'cough center'

The Workshop considered the mechanisms whereby the 'cough center' could be tuned by various afferent inputs. There were particular presentations on the effects of inputs from the nose, mouth, respiratory tract and lungs, cerebral cortex, somatic tissues and the pharynx. From all these sites cough induced from the lungs could be increased or decreased in its strength or modified in its pattern. Thus 'tuning' of cough could be due to the interaction of afferent inputs, or to the sensitization or desensitization of brainstem neural pathways. The pattern of response depended on the 'type' of cough being studied and, in some instances, on the timing of the sensory input into the brainstem. Cough inputs could also affect various 'non-cough' motor outputs from the brain, although this was not the main theme of the Workshop. The main conclusion was that cough is not a stereotyped output from the medullary 'cough center', but that its pattern and strength depend on many afferent inputs acting on the 'cough center'.

Heart rate variability in hypertension caused by sleep disordered breathing and its modification by CPAP

OBJECTIVES

1) To analyze heart rate variability (HRV) changes, reflecting the sympathovagal balance with secondary hypertension caused by sleep disordered breathing (SDB), compared to healthy controls and essential hypertension without SDB; 2) to compare HRV changes between various degrees of SDB severity; and 3) to test the modification of HRV indices by continuous positive airway pressure (CPAP) in SDB patients.

BACKGROUND

Differentiation of secondary hypertension caused by SDB from essential hypertension and healthy controls by ambulatory blood pressure measurement (ABPM) and its modification by CPAP, requires an analysis of HRV changes, as frequently used for the prediction of cardiovascular risk.

METHODS

HRV changes were analyzed in 48 adults divided into six groups according to the apnoea/hypopnoea index (AHI), i.e. three groups with various degrees of SDB, a group with severe SDB after CPAP application, a group with essential hypertension without SDB, and a group of healthy controls. Night-time and daytime values of low frequency (LF) and high frequency (HF) bands and the LF/HF ratio were compared in the six groups.

RESULTS

The night-time values of LF bands were higher in severe than in moderate and mild degrees of SDB, and the correlation of LF/HF ratio with AHI (r = 0.3511) suggests the gradual increase of sympathetic predominance with the severity of SDB. The high sympathetic activity substantially decreased after application of CPAP in severe SDB.

CONCLUSION

The increased nocturnal values of the LF band and the LF/HF ratio, caused by frequent apnoea/ hypopnoea episodes, support the usefulness of HRV spectral analysis for the prediction of cardiovascular risk in patients with SDB (Tab. 1, Fig. 3, Ref. 36).

Distinct generators for aspiration and expiration reflexes: localization, mechanisms and effects

Re-evaluation of our earlier c-Fos-like immuno-reactive studies and brainstem transection/lesion experiments in over 40 anaesthetized, non-paralyzed cats allowed comparison of two distinct airway defensive reflexes with the distinct generators for inspiration (I) and expiration (E), described recently in juvenile rats. The spiration reflex (AspR) is characterized by solitary rapid and strong inspiratory effort with a reciprocal inhibition, preventing a subsequent active expiration, while the expiration reflex (ExpR) manifests by rapid and strong expiratory effort, starting without a preceding, inspiration, or reciprocal inhibition of occasional spontaneous inspiration. The retro-trapezoid nucleus/parafacial respiratory group neurones described as the distinct generator for active E in rats, are activated also during the ExpR in adult cats. Brainstem transection 5 mm above the obex eliminates the E generator and the ExpR, but preserves the I generator located in the pre-Bötzinger Complex, and also the AspR. This suggests the existence of a distinct I generator in cats as well as rats, and its contribution to the generation of the AspR. Persistence of the AspR in adult cats during asphyxic gasping, their similar character and the strong activation of I neurones at many places in the medulla and pons, suggest a common brainstem neuronal circuit contributing to generation of both the gasping and the gasp-like AspR. That the AspR and ExpR have distinct multilevel brainstem control mechanisms supports the dual theory of control and provides unique models for testing respiratory rhythm and pattern generation. The AspR may be compared with the powerful "auto-resuscitation effects of asphyxic gasping"; the ExpR may underly the effectiveness of the laryngeal chemoreflexes in prevention of lung diseases.

Cough: what's in a name?

The cough reflex (CR) and the expiration reflex (ER) are two defensive reflexes from the respiratory tract, the latter mainly from the larynx. Both are elicited by mechanical and chemical irritation of the airway mucosa, and are a characteristic of airway diseases, but they have different functions. The CR first draws air into the lungs, to accentuate the subsequent expulsive phase; the ER consists of a strong expiration, to prevent aspiration of material into the lungs. They have different sensory pathways, central nervous circuits, and physiological and pharmacological modulations. In practice, coughing often consists of a combination of the two reflexes, a cough bout, epoch or attack. Articles on cough usually do not distinguish between the two reflexes, or whether the coughs are single events or epochs; they usually only measure frequency of expiratory efforts, and neglect other aspects. Current methods for measuring and assessing cough are described, with indications of when the use of these methods may be important.

Airway reflexes, autonomic function, and cardiovascular responses

In this article, we review the cardiovascular responses to the inhalation of irritants and pollutants. Many sensory receptors in the respiratory system, from nose to alveoli, respond to these irritants and set up powerful reflex changes, including those in the cardiovascular system. Systemic hypotension or hypertension, pulmonary hypertension, bradycardia, tachycardia, and dysrhythmias have all been described previously. Most of the experiments have been acute and have been performed on anesthetized experimental animals. Experiments on humans suggest we have similar sensory systems and reflex responses. However, we must use caution when applying the animal results to humans. Most animal experiments, unlike those with humans, have been performed using general anesthesia, with irritants administered in high concentrations, and often to a restricted part of the respiratory tract. Species differences in the response to irritants are well established. We must be even more careful when applying the results of acute experiments in animals to the pathophysiologic changes observed in prolonged exposure to environmental pollution in humans.

Airway reflexes, autonomic function, and cardiovascular responses

In this article, we review the cardiovascular responses to the inhalation of irritants and pollutants. Many sensory receptors in the respiratory system, from nose to alveoli, respond to these irritants and set up powerful reflex changes, including those in the cardiovascular system. Systemic hypotension or hypertension, pulmonary hypertension, bradycardia, tachycardia, and dysrhythmias have all been described previously. Most of the experiments have been acute and have been performed on anesthetized experimental animals. Experiments on humans suggest we have similar sensory systems and reflex responses. However, we must use caution when applying the animal results to humans. Most animal experiments, unlike those with humans, have been performed using general anesthesia, with irritants administered in high concentrations, and often to a restricted part of the respiratory tract. Species differences in the response to irritants are well established. We must be even more careful when applying the results of acute experiments in animals to the pathophysiologic changes observed in prolonged exposure to environmental pollution in humans.

Reflexes from airway rapidly adapting receptors

Rapidly adapting receptors (RARs) occur throughout the respiratory tract from the nose to the bronchi. They have thin myelinated nerve fibres, an irregular discharge and adapt rapidly to a maintained volume stimulus, but often slowly to a chemical stimulus. They are polymodal, responding to mechanical and chemical irritant stimuli, and to many inflammatory and immunological mediators. RARs show very varied sensitivities to different stimuli, and diverse reflex responses. Those in the larynx are usually called 'irritant' receptors. They probably cause cough, the expiration reflex and other laryngeal reflexes: cardiovascular, mucus secretion, bronchoconstrictor and laryngoconstrictor. Those in the trachea and larger bronchi are very mechanosensitive; they cause cough, bronchoconstriction and airway mucus secretion. Those in the larger bronchi are more chemosensitive; they may cause cough, but also stimulate hyperventilation, augmented breaths, mucus secretion, bronchoconstriction and laryngeal closure. Most of the stimuli to RARs also affect other airway receptors, especially those with C-fibre afferents, and the total reflex response will be the additive affect of all these reflexes.

Airway receptors

There are many types of afferent receptor in the airways; at least five in the larynx: pressure, drive, cold, irritant and C-fibre; and at least four in the trachea and bronchi: slowly and rapidly adapting stretch receptors (SARs and RARs), C-fibre receptors, and those in neuroepithelial bodies (NEBs). Histologically enough sensory structures have been identified to account for the various patterns of afferent activity, but most correlations are poor. For the larynx, four or more sensory structures have not definitively been identified with afferent discharges and reflex responses. For the trachea and bronchi, only SARs have been clearly identified morphologically and physiologically. The reflexes and afferent discharges from RARs and C-fibre receptors are fairly clear, some at least of the sensory terminals lie in the epithelium, but receptor complexes have not been mapped out. Nerves in NEBs have been identified, but not their local and central reflex actions.

Upper airway reflexes

It is usually assumed that upper airway pressure receptors mediate the reflexes involved in sleep apneas, but many other receptors may be involved, including those responding to chemical stimuli. The reflexes to upper airway negative pressure have been further studied, and the timing of their inputs shown to be important. Their effects on the cardiovascular system, including cerebral blood flow, have been emphasized. The central nervous pathways for the upper airway reflexes and their relationship to the neuronal circuits of the respiratory rhythm generator are being analyzed, but no clear pattern has emerged. Many neurotransmitters have been identified, usually on the motor pathways, which points to possible therapeutic approaches. The central nervous pharmacology and the neuronal pattern for the cough reflex have been described, and a similar approach to other upper airway reflexes, especially those involved in sleep apneas, would be valuable.

Drug uptake from the airways and lungs

This paper reviews the mechanisms and physiological processes that act when drugs or chemicals are administered into the lower airways and lungs. Administration is usually by aerosol. Agents can be given, for example, either to treat pulmonary diseases such as asthma, or the test for airways' responsiveness or other functions, or as a means of access of a drug to the systemic circulation. The first barrier to absorption is the airway surface liquid, including mucus. The thickness of this layer will determine the concentration of the drug in solution, and therefore its rate of entry into the tissue. The agent must then penetrate the airway epithelium, the strongest barrier for hydrophilic agents. Agents must then diffuse through the epithelial basement membrane and the interstitium. Finally, the agent may be taken up into the mucosal vasculature, and changes in blood flow will influence its uptake and distribution. If the drug is to reach a target organ, such as airway smooth muscle or glands, these barriers have first to be traversed.

Microvascular anatomy of the nose

The microvasculature of the nose consists of: 1) A dense subepithelial network of capillaries, with fenestrations between the endothelial cells. This network provides nutrients to the epithelium and glands, and allows passage of water into the lumen for evaporation and air-conditioning. 2) A system of capacitance vessels or sinuses, which when they distend, block the nasal lumen, and when they empty, open the nasal passages. Changes in their volume will affect the filtering and air-conditioning functions of the nose. 3) Arteriovenous anastomoses which allow rapid passage of blood through the mucosa. They are probably important in air-conditioning, and in the countercurrent mechanisms that tend to keep the brain cool in a hot dry climate. The anatomical interrelationships between these different systems is not well understood, nor is their differential control in terms of actions of mediators and nerves. In neurogenic inflammation sensory nerves are excited and release local mediators such as substance P via axon reflexes. These sensory neuropeptides will cause vasodilatation, vascular congestion and extravasation of liquid from the postcapillary venules, with resultant oedema and exudate. They may also cause secretion from the submucosal glands.

Estimation of thickness of airway surface liquid in ferret trachea in vitro

The tracheae of ferrets and rabbits were mounted in vitro in organ baths. While the tracheae were liquid filled, the permeability coefficient ( P) was determined, and then while the tracheae were air filled, the percent clearance for 99mTc-labeled diethylenetriaminepentaacetic acid (DTPA) was determined. The thickness of airway surface liquid (ASL) was estimated by three methods. 1) The initial concentration of 99mTc-DTPA and the total amount of 99mTc-DTPA (the sum of that entering the outside medium, that draining from the trachea, and that washed out at the end of 40 min) gave the initial volume of ASL and thus its thickness. Mean values were 45.7 micron for the ferret and 41.9 micron for the rabbit. 2) Estimates of ASL thickness at the end of the 40-min period, based on the final 99mTc-DTPA concentration and the amount in the washout, were 42.9 micron for ferret and 45.4 micron for rabbit. 3) The ratio of P to percent clearance gave mean ASL thickness values of 49.2 micron for the ferret and 40.3 micron for the rabbit. Thus three separate methods for determining ASL thickness give very similar results, with means in the range 40-49 micron. Administration of methacholine or atropine to ferret tracheae did not significantly change ASL thickness.

Actions of moguisteine on cough and pulmonary rapidly adapting receptor activity in the guinea pig

With anaesthetized guinea pigs, the actions of moguisteine were tested on the cough reflex, the resting discharge of lung rapidly adapting receptors (RARs), RAR activity induced by aerosols of capsaicin, stimulation of RARs due to i.v. injection of capsaicin, and on the reflex responses to i.v. capsaicin. I.v. moguisteine (20 microg kg(-1)), compared with vehicle, decreased the spontaneous firing of RARs. Intragastric (i.g.) moguisteine (200 mg kg(-1)) had no effect on resting discharge. I.g. moguisteine depressed the cough response due to capsaicin aerosol (0.01(-1) mg ml(-1)) and significantly reduced the increased discharge of the RARs due to the aerosol. I.v. and i.g. moguisteine reduced the proportionate increase in RAR discharge due to i.v. capsaicin (50 microg kg(-1)). It did not appreciably affect the cardiovascular and respiratory responses to i.v. capsaicin, which presumably activated lung C-fibre receptors. We conclude that the antitussive action of moguisteine is mediated at least in part by a decrease in the excitatory response of RARs to tussive stimuli.

Drug uptake in the trachea

For hydrophilic drugs and agents the major barrier to diffusion from the airway lumen into the mucosa is the epithelium, but for lipophilic agents epithelial permeability is high. Destruction of the epithelium increases the permeability of hydrophilic but not lipophilic agents. Changes in mucosal blood flow, induced either by vasoactive drugs or by changing the rate of arterial perfusion, lead to changes in drug uptake from the lumen to venous blood. Increases in flow decrease uptake, and vice versa for decreases in flow. The most likely explanation of this apparently paradoxical result is that increases in vascular pressure and flow result in a greater interstitial liquid volume and thus perfusion barrier, and induce solvent drag across the vascular endothelial wall, which will limit uptake of agents into the vascular lumen.

Airway and alveolar permeability and surface liquid thickness: theory

The thickness of airway surface liquid (ASL) can be calculated as the ratio of the permeability coefficient of an absorbed inert tracer to the percentage rate in which it decreases in content in the airway lumen. The percentage clearance of radiolabeled diethylenetriaminepentaacetic acid (DTPA) from human airways or lungs has been measured many times, with a mean value of 1.04 +/- 0.25 (SD) %/min. Rates of clearance from animal lungs of most species give values of the same order, although they are lower in the sheep and higher in the dog. Permeability coefficients have not been measured simultaneously with percentage clearances and not at all for human tissues. Values for mannitol and sucrose, of which the former gives a permeability coefficient approximately 25% greater than that for sucrose and DTPA in airway tubes and isolated mucosal sheets from experimental animals, give a mean approximately 7.1 x 10(-7) cm/s. This corresponds to thickness of ASl of approximately 20-150 microns for various species. The assumptions underlying this estimate are discussed. It is concluded that ASL thickness in vivo may be considerably greater than in vitro measurements involving rapid freezing of the airway wall. Estimates of alveolar permeability suggest that either it is very considerably lower than that of the airway epithelium, that methods to measure alveolar permeability mainly reflect airway permeability, or both.

The tracheobronchial vasculature: a possible role in asthma

The tracheobronchial microcirculation consists of a subepithelial capillary network and in some species deeper capacitance vessels and an adventitial network. Postcapillary venules are the main site of plasma extravasation in inflammatory conditions. There are surprising species differences. The subepithelial capillary network is dense in species such as sheep and dog but relatively scanty in rabbit and humans. Sheep have conspicuous capacitance vessels or blood sinuses, especially in the trachea and at points of bronchial branching with walls that lack smooth muscle. The rabbit also has a well-developed capacitance system but the blood sinuses have thick muscular walls. Although the capacitance system in humans has not been studied much it is probably present with muscular walls. It is absent in rats but present in guinea pigs. Thus, in some species the tracheobronchial vasculature may give the mucosa an erectile capacity, as in the nose of each species. Arteriovenous anastomoses (AVA) cannot be demonstrated physiologically in sheep but they seem to be present as thoroughfare vessels in rats and guinea pigs. Whether they exist in humans is not known. The absence of AVA might indicate a weak or absent thermoregulatory and air conditioning role for the lower airway vasculature. Extensive studies of neurogenic inflammation in rodents show that sensory neuropeptides can open gaps between the endothelial cells of postcapillary venules and the same change can be caused by a large number of inflammatory mediators. These opened gaps cause extravasation of plasma into the interstitium. Small increases in interstitial pressure lead to spaces opening between the epithelial cells and exudation of plasma into the airway lumen. The role of the airway microvasculature in asthma is controversial. Cold and hyperosmolar solutions cause vasodilatation as do the mediators released in the mucosal inflammation of asthma. However, quantitation of the thickening of the airway wall due to vascular engorgement, mucosal edema, or increased luminal liquid does not prove that these changes are a cause of airway obstruction. The contraction of airway smooth muscle superimposed on the mucosal inflammatory pathology might lead to a synergistic mechanism to increase airway resistance.

Relationships among the composition of mucus, epithelial lining liquid, and adhesion of microorganisms

Airway surface liquid (ASL) is complex and comes from many sources, in particular glands and epithelium. The mucoglycoproteins present bind to bacteria. Bacterial membranes contain adhesins that bind to receptors on the mucus. The bound bacteria multiply and release toxins that diffuse to the epithelium and damage or destroy it, inhibiting mucociliary transport. The damaged epithelium releases products such as phospholipids into the ASL. These change the physical properties of the mucus and also promote mucus secretion, which may block smaller airways. Airway surface liquid contains constituents such as immunoglobulins, lysozyme, and lactoferrin and neutrophil products such as proteases that act on bacteria. Few bacteria adhere to healthy epithelium. To adhere, most require damaged tissue with membrane receptors that encourage bacterial invasion. If the epithelium is destroyed, bacteria adhere to the basement membrane or extracellular matrix. A damaged epithelium can also cause hyperresponsiveness of airway secretory mechanisms, with increased gland secretion that in turn interacts with the bacteria.

New perspectives on basic mechanisms in lung disease. 4. Why are the airways so vascular?

Images

Physiologic control. Anatomy and physiology of the airway circulation

Both for the nose and the lower airways there is an extensive subepithelial capillary network. That for the nose is fenestrated, and this is true for the tracheobronchial tree of rats, guinea pigs, and hamsters, and for that of human asthmatics. However, healthy humans, dogs, and sheep have capillaries without fenestrations except for those close to neuroepithelial bodies and submucosal glands. Deeper in the mucosa there is a capacitance system of vessels, conspicuous in the nose but present also in the lower airways of rabbits and sheep and, to a lesser extent, in those of dogs and humans. Both for the nose and the lower airways, parasympathetic nerves are vasodilator, sympathetic nerves are vasoconstrictor, and sensory nerves are able to release dilator neuropeptides. Most inflammatory and immunologic mediators are vasodilator. A conspicuous difference between the nasal and lower airway vasculatures is the presence of arteriovenous anastomoses only in the former. Countercurrent mechanisms also exist in the nose to increase its efficiency in air conditioning, but they have not been established for the trachea. The pulmonary vasculature could be part of such a system for the bronchi. Distension of the airway vasculature thickens the mucosa, probably both by vascular distension and by edema formation. The latter can lead to exudation into the airway lumen. These processes have not been well quantitated, and the balance sheet of capillary and capacitance vessel volumes, interstitial liquid volume, and exudate volume needs to be worked out in physiologic and pathologic conditions.

Afferent neural pathways in cough and reflex bronchoconstriction

Cough and bronchoconstriction are airway reflexes that protect the lung from inspired noxious agents. These two reflexes can be evoked both from the larynx and tracheobronchial tree and also from some extrarespiratory sites. Within the airways, certain sites are particularly sensitive to stimulation of cough (larynx and points of proximal airway branching), whereas bronchoconstriction can be triggered from the whole of the tracheobronchial tree. In the larynx, "irritant" receptors with myelinated afferents mediate cough and bronchoconstriction. Little seems to be known about laryngeal nonmyelinated afferents and their reflexes. In the tracheobronchial tree and lung, slowly adapting stretch receptors (SARs) and rapidly adapting stretch receptors (RARs) have opposing effects on airway tone, the former mediating bronchodilation and the latter bronchoconstriction. In cough, on the other hand, they operate concurrently, a mediatory role for RARs and a facilitatory role for SARs. C-fiber endings (bronchial and pulmonary) mediate bronchoconstriction. Inhalation of so-called "selective" C-fiber stimulants induces cough, but excitation of RARs has not been eliminated, and the possibility also exists that the cough is secondary to other lung actions mediated by these nerve endings. Although cough and bronchoconstriction may be mediated by the same type of receptor, they seem to have separate afferent neural pathways.

Cyclic adenosine monophosphate-dependent kinase in cystic fibrosis tracheal epithelium

Cl-impermeability in cystic fibrosis (CF) tracheal epithelium derives from a deficiency in the beta-adrenergic regulation of apical membrane Cl- channels. To test the possibility that cAMP-dependent kinase is the cause of this deficiency, we assayed this kinase in soluble fractions from cultured airway epithelial cells, including CF human tracheal epithelial cells. Varying levels of cAMP were used in these assays to derive both a Vmax and apparent dissociation constant (Kd) for the enzymes in soluble extracts. The cAMP-dependent protein kinase from CF human tracheal epithelial cells has essentially the same Vmax and apparent Kd as non-CF human, bovine, and dog tracheal epithelial cells. Thus, the total activity of the cAMP-dependent kinases and their overall responsiveness to cAMP are unchanged in CF.

Effects of inflammatory and other mediators on airway vascular beds

The bronchial arteries extend to all lung structures in man with the exception only of the alveolar wall. In addition to providing nutrition to the lungs, the bronchial vessels can also function as a hemodynamic and gas-exchange system due to anastomoses with the pulmonary arteries; they also play a significant role in controlling the clearance of chemical mediators, regulating the development of airway wall edema, and controlling heat exchange in the tracheobronchial tree. We have measured the effects of inflammatory and other mediators on tracheal mucosal thickness and the changes in tracheal vascular resistance in dogs. Bradykinin, histamine, and methacholine had large "vasodilator" effects, decreasing vascular resistance, and they also clearly increased the thickness of the mucosa. Substance P, VIP, PGF2 alpha, and PGE1 had as large a response on vascular resistance as the drugs mentioned above, but only had small effects in increasing tracheal mucosal thickness. Salbutamol fell between these 2 groups with regard to the pattern of response. Phenylephrine had an opposite action, causing an increase in vascular resistance and a decrease in mucosal thickness. Despite the vasodilatation and the increase in vascular permeability due to vasoactive drugs, the changes in mucosal thickness were rather small and could not be correlated with the decreases in vascular resistance due to the different drugs. Such changes are unlikely to have an appreciable effect on tracheal airway resistance. The change in mucosal thickness may be more significant in those parts of the airways where the ratio of change in mucosal thickness to the radius of adjacent lumen is large, such as the nose and small conducting airways.

Control of airway caliber

Tracheobronchial smooth muscle tone may be affected by 4 nervous mechanisms: (1) Vagal cholinergic parasympathetic nerves, which are the main agents for resting tone and most reflex bronchoconstrictions. Their activity is blocked by atropinic drugs. (2) Sympathetic adrenergic dilator nerves, which may act mainly on beta-adrenoceptors in the pulmonary bronchi; alternatively, they may inhibit ganglionic transmission in the vagal constrictor pathway. (3) Vagal nonadrenergic dilator nerves (NAIS). The neurotransmitter at these nerves is probably vasoactive intestinal polypeptide (VIP), although purines could be involved. The role of this system in physiologic and pathologic conditions has not been established. (4) Local axon constrictor reflexes in afferent nerves. These respond to mucosal irritation and cause local smooth muscle contraction by release of substance P. Their importance has not yet been assessed. The motor innervation of the airways is activated reflexly by many stimuli, some of which cause constriction and others dilation. Most of the reflexes are blocked by atropine, which suggests that the cholinergic constrictor pathway is dominant. Other responses include changes in laryngeal caliber and secretion of mucus. Aspirations into the airways will lead to bronchoconstriction, laryngospasm, and secretion of mucus, as well as to respiratory and cardiovascular reflexes. The balance, effectiveness, and development of these responses requires much further study.