Exercise-induced asthma: a difference in opinion regarding the stimulus

Inhaled Medicines: Past, Present, and Future

The purpose of this review is to summarize essential pharmacological, pharmaceutical, and clinical aspects in the field of orally inhaled therapies that may help scientists seeking to develop new products. After general comments on the rationale for inhaled therapies for respiratory disease, the focus is on products approved approximately over the last half a century. The organization of these sections reflects the key pharmacological categories. Products for asthma and chronic obstructive pulmonary disease include β -2 receptor agonists, muscarinic acetylcholine receptor antagonists, glucocorticosteroids, and cromones as well as their combinations. The antiviral and antibacterial inhaled products to treat respiratory tract infections are then presented. Two "mucoactive" products-dornase α and mannitol, which are both approved for patients with cystic fibrosis-are reviewed. These are followed by sections on inhaled prostacyclins for pulmonary arterial hypertension and the challenging field of aerosol surfactant inhalation delivery, especially for prematurely born infants on ventilation support. The approved products for systemic delivery via the lungs for diseases of the central nervous system and insulin for diabetes are also discussed. New technologies for drug delivery by inhalation are analyzed, with the emphasis on those that would likely yield significant improvements over the technologies in current use or would expand the range of drugs and diseases treatable by this route of administration. SIGNIFICANCE STATEMENT: This review of the key aspects of approved orally inhaled drug products for a variety of respiratory diseases and for systemic administration should be helpful in making judicious decisions about the development of new or improved inhaled drugs. These aspects include the choices of the active ingredients, formulations, delivery systems suitable for the target patient populations, and, to some extent, meaningful safety and efficacy endpoints in clinical trials.

Mechanisms and Biomarkers of Exercise-Induced Bronchoconstriction

Exercise is a common trigger of bronchoconstriction. In recent years, there has been increased understanding of the pathophysiology of exercise-induced bronchoconstriction. Although evaporative water loss and thermal changes have been recognized stimuli for exercise-induced bronchoconstriction, accumulating evidence points toward a pivotal role for the airway epithelium in orchestrating the inflammatory response linked to exercise-induced bronchoconstriction. Overproduction of inflammatory mediators, underproduction of protective lipid mediators, and infiltration of the airways with eosinophils and mast cells are all established contributors to exercise-induced bronchoconstriction. Sensory nerve activation and release of neuropeptides maybe important in exercise-induced bronchoconstriction, but further research is warranted.

Repurposing excipients as active inhalation agents: The mannitol story

The story of how we came to use inhaled mannitol to diagnose asthma and to treat cystic fibrosis began when we were looking for a surrogate for exercise as a stimulus to identify asthma. We had proposed that exercise-induced asthma was caused by an increase in osmolarity of the periciliary fluid. We found hypertonic saline to be a surrogate for exercise but an ultrasonic nebuliser was required. We produced a dry powder of sodium chloride but it proved unstable. We developed a spray dried preparation of mannitol and found that bronchial responsiveness to inhaling mannitol identified people with currently active asthma. We reasoned that mannitol had potential to replace the 'osmotic' benefits of exercise and could be used as a treatment to enhance mucociliary clearance in patients with cystic fibrosis. These discoveries were the start of a journey to develop several registered products that are in clinical use globally today.

Down-Regulation of Cough during Exercise Is Less Frequent in Healthy Children than Adults. Role of the Development and/or Atopy?

Cough is typically associated with physical activity in children with asthma, but the characteristics of the relationship between cough and exercise has not been established under physiological conditions. The aim of the study was to describe the effect of exercise on the reflex cough response elicited by a single breath of capsaicin in non-asthmatic children. A group of non-asthmatic adults was studied as reference. Thirty children and 29 adults were recruited. The cough reflex sensitivity to capsaicin was first determined to establish the dose that provokes 5 cough efforts (C5). The number of coughs elicited by C5 (NC5) was then compared at baseline and during a standardized submaximal treadmill exercise. Data are expressed as median (interquartile range). Children and adults showed a significant decrease in NC5 (respectively from 5.0 (4.0–6.0) to 2.5 (2.0–4.0), p < 0.0005 and from 6.0 (5.0–7.0) to 2.0 (0.0–3.0, p < 0.0005). During exercise, NC5 was observed to decrease in all adult subjects, but in only 24/30 children (80%, p = 0.02). A trend for a higher incidence of personal and familial atopy was observed in children that lacked cough down-regulation during exercise compared with other children. It is concluded that the cough reflex response to capsaicin is down regulated by exercise in both children and adults. The effect however is less consistently observed in the former. The difference may reflect maturation of descending inhibitory pathways of the cough reflex, but may also be associated to atopy. The data stress the importance of assessing the time relationship of cough and exercise in questionnaire studies of asthma.

'Indirect' challenges from science to clinical practice

Indirect challenges act to provoke bronchoconstriction by causing the release of endogenous mediators and are used to identify airway hyper-responsiveness. This paper reviews the historical development of challenges, with exercise, eucapnic voluntary hyperpnoea (EVH) of dry air, wet hypertonic saline, and with dry powder mannitol, that preceded their use in clinical practice. The first challenge developed for clinical use was exercise. Physicians were keen for a standardized test to identify exercise-induced asthma (EIA) and to assess the effect of drugs such as disodium cromoglycate. EVH with dry air became a surrogate for exercise to increase ventilation to very high levels. A simple test was developed with EVH and used to identify EIA in defence force recruits and later in elite athletes. The research findings with different conditions of inspired air led to the conclusion that loss of water by evaporation from the airway surface was the stimulus to EIA. The proposal that water loss caused a transient increase in osmolarity led to the development of the hypertonic saline challenge. The wet aerosol challenge with 4.5% saline, provided a known osmotic stimulus, to which most asthmatics were sensitive. To simplify the osmotic challenge, a dry powder of mannitol was specially prepared and encapsulated. The test pack with different doses and an inhaler provided a common operating procedure that could be used at the point of care. All these challenge tests have a high specificity to identify currently active asthma. All have been used to assess the benefit of treatment with inhaled corticosteroids. Over the 50 years, the methods for testing became safer, less complex, and less expensive and all used forced expiratory volume in 1 sec to measure the response. Thus, they became practical to use routinely and were recommended in guidelines for use in clinical practice.

Air quality and temperature effects on exercise-induced bronchoconstriction

Exercise-induced bronchoconstriction (EIB) is exaggerated constriction of the airways usually soon after cessation of exercise. This is most often a response to airway dehydration in the presence of airway inflammation in a person with a responsive bronchial smooth muscle. Severity is related to water content of inspired air and level of ventilation achieved and sustained. Repetitive hyperpnea of dry air during training is associated with airway inflammatory changes and remodeling. A response during exercise that is related to pollution or allergen is considered EIB. Ozone and particulate matter are the most widespread pollutants of concern for the exercising population; chronic exposure can lead to new-onset asthma and EIB. Freshly generated emissions particulate matter less than 100 nm is most harmful. Evidence for acute and long-term effects from exercise while inhaling high levels of ozone and/or particulate matter exists. Much evidence supports a relationship between development of airway disorders and exercise in the chlorinated pool. Swimmers typically do not respond in the pool; however, a large percentage responds to a dry air exercise challenge. Studies support oxidative stress mediated pathology for pollutants and a more severe acute response occurs in the asthmatic. Winter sport athletes and swimmers have a higher prevalence of EIB, asthma and airway remodeling than other athletes and the general population. Because of fossil fuel powered ice resurfacers in ice rinks, ice rink athletes have shown high rates of EIB and asthma. For the athlete training in the urban environment, training during low traffic hours and in low traffic areas is suggested.

Exercise-induced bronchoconstriction: celebrating 50 years

This article examines in detail the history of more than half a century of investigations into elucidating the causation of exercise-induced bronchoconstriction. Despite earnest attempts by many researchers from many countries, answers to some pivotal questions await the next generation of investigators into exercise-induced bronchoconstriction.

Assessment of EIB: What you need to know to optimize test results

Respiratory symptoms and asthma control questionnaires are poor predictors of the presence or severity of exercise-induced bronchoconstriction (EIB), and objective measurement is recommended. To optimize the chance of a positive test result, there are several factors to consider when exercising patients for EIB, including the ventilation achieved and sustained during exercise, water content of the inspired air, and the natural variability of the response. The high rate of negative exercise test results has led to the development of surrogates to identify EIB in laboratory or office settings, including eucapnic voluntary hyperpnea of dry air and inhalation of hyperosmolar aerosols.

Assessment of exercise-induced bronchoconstriction in adolescents and young children

Recent research shows important differences in exercise-induced bronchoconstriction (EIB) between children and adults, suggesting a different pathophysiology of EIB in children. Although exercise can trigger classic symptoms of asthma, in children symptoms can be subtle and nonspecific; parents, children, and clinicians often do not recognize EIB. With an age-adjusted protocol, an exercise challenge test can be performed in children as young as 3 years of age. However, an alternative challenge test is sometimes necessary to assess potential for EIB in children. This review summarizes age-related features of EIB and recommendations for assessing EIB in young children and adolescents.

Mechanisms and management of exercise-induced asthma in elite athletes

OBJECTIVE AND METHODS

Asthma is often reported by elite athletes, especially endurance athletes. The aim of this article is to review current knowledge of mechanisms and management of exercise-induced asthma (EIA) in adult elite athletes.

RESULTS

The mechanisms underlying EIA is incompletely understood, but the two prevailing hypotheses are the hyper-osmolarity and the thermal hypothesis. Both hypotheses consider inflammation and activation of mast cells as being crucial for the development of EIA, although the assumed mechanisms triggering the inflammatory response differ. Objective testing is of utmost importance in the diagnosis of EIA in elite athletes. Management of EIA can be divided into pharmacologic and non-pharmacologic treatment. The basic principles for the treatment of EIA in elite athletes should be as for any asthmatic individual, including use of inhaled corticosteroids (ICS), β(2)-agonists, and leukotriene antagonists. However, evidence suggests that daily use of β(2)-agonists might lead to the development of tolerance. ICS therapy is, due to its anti-inflammatory effects, the recommended primary therapy for EIA also in elite athletes. All doctors treating individuals with asthma, especially elite athletes, should remain updated on doping aspects of asthma therapy. Non-pharmacologic management of EIA in elite athletes includes physical warm-up, which takes advantage of the refractory period following an attack of EIA, whereas high intake of antioxidants may reduce airway inflammation. Wearing heat masks, specially designed for outdoor winter athletes, might protect against bronchoconstriction triggered by inhalation of cold and dry air.

CONCLUSION

EIA in elite athletes should be managed as in any individual with asthma, but the risk of developing tolerance to bronchodilators as well as doping aspects should always be taken into account.

Cough response to isocapnic hyperpnoea of dry air and hypertonic saline are interrelated

Background

Mechanisms behind asthmatic cough are largely unknown. It is known that hyperosmolar challenges provoke cough in asthmatic but not in the healthy subjects. It has been postulated that isocapnic hyperpnea of dry air (IHDA) and hypertonic aerosols act via similar mechanisms in asthma to cause bronchoconstriction. We investigated whether there is an association between cough response induced by IHDA and hypertonic saline (HS) challenges.

Methods

Thirty-six asthmatic and 14 healthy subjects inhaled HS solutions with increasing osmolalities administered via ultrasonic nebuliser until 15 cumulative coughs were recorded. The IHDA consisted of three three-minute ventilation steps: 30%, 60% and 100% of maximal voluntary ventilation with an end-point of 30 cumulative coughs. The challenges were performed on separate days at least 48 hours between them and within one week. Inhaled salbutamol (400 mcg) was administered before the challenges to prevent bronchoconstriction. The cough response was expressed as the cough-to-dose ratio (CDR) which is the total number of coughs divided by the maximal osmolality inhaled or the maximal ventilation achieved.

Results

Cough response to IHDA correlated with the HS challenge (Rs = 0.59, p < 0.001). Cough response to IHDA was at its strongest during the first minute after the challenge. IHDA induced more cough among asthmatic than healthy subjects CDR being (mean ± SD) 0.464 ± 0.514 and 0.011 ± 0.024 coughs/MVV%, p < 0.001, respectively. Salbutamol effectively prevented bronchoconstriction to both challenges.

Conclusions

Asthmatic patients are hypersensitive to the cough-provoking effect of hyperpnoea, as they are to hypertonicity. Cough response induced by IHDA and HS correlated well suggesting similar mechanisms behind the responses.

Lung Deposition of Mannitol Powder Aerosol in Healthy Subjects

Mannitol as a dry powder aerosol is used for bronchoprovocation testing and to enhance mucus clearance in people with excessive airway secretions. The dose and distribution of the deposited aerosol in the lung was investigated using fast single photon emission tomography (SPECT) imaging. Mannitol powder (3 microm particle size) was produced by spray drying and radiolabeled with (99m)Tc-DTPA. Approximately 60 mg of radiolabeled mannitol (containing 52-68 MBq of (99m)Tc-DTPA) was administered to 10 healthy subjects using the Inhalator dry powder inhaler (DPI), and SPECT images (1 min each) were collected. Thirteen percent to 31% of the dose of mannitol loaded in the inhaler deposited in the lungs and the deposited dose correlated positively with the peak inhalation air flow. The regional aerosol lung distribution, as expressed by the penetration index (i.e., ratio of peripheral to central deposition in the lung) varied from 0.31 to 0.88, which however showed no dependency on any flow parameters. The variation in response to the same dose of mannitol within the asthmatic population may in part be explained by these findings.

How does exercise cause asthma attacks?

PURPOSE OF REVIEW

To remind readers that evaporative water loss from the airway surface is the stimulus for exercise-induced bronchoconstriction. To emphasize that recruitment of the peripheral airways determines severity of exercise-induced bronchoconstriction. To draw attention to the potential for injury of the epithelium and for plasma exudation to contribute to the pathogenesis of exercise-induced bronchoconstriction in athletes. To emphasize that many inflammatory mediators are involved in exercise-induced bronchoconstriction and that some are found in both asthmatic and healthy subjects.

RECENT FINDINGS

That inflammatory mediators are released into the airways in response to exercise and can be measured by inducing sputum (histamine, cysteinyl leukotrienes) or collecting condensate from exhaled air (cysteinyl leukotrienes and adenosine). The concentration of mediators was reduced in response to a combination of loratadine and montelukast. Exercise is a stimulus for upregulating the genes coding for the 5-lipoxygenase pathway in healthy subjects.

SUMMARY

Dehydration of the airways results in release of mediators. The likely source of these mediators is the mast cell. Epithelial injury occurs in exercise-induced bronchoconstriction. The process of repair may contribute to the development of airway hyperresponsiveness in healthy subjects. Measuring the airway response to exercise, or a surrogate for exercise, as an indicator of airway hyperresponsiveness is warranted in patients with symptoms of asthma.

Long-acting beta 2-adrenoceptor agonists and exercise-induced asthma: lessons to guide us in the future

The safety and efficacy of long-acting beta(2)-adrenoceptor agonists (LABAs) taken intermittently for the prevention of exercise-induced asthma (EIA) in children is well established. However, the safety and efficacy of LABAs taken twice daily, either alone or in combination with inhaled corticosteroids, for the prevention of EIA is not as clear because of issues of tolerance (defined as being less responsive to the influence of LABAs). There have been many observations on short-acting beta(2)-adrenoceptor agonists (SABAs) and EIA that should have alerted us to the potential for tolerance and desensitization to occur with LABAs. For example, we expected that the use of LABAs for EIA would overcome the problem of the short duration of protection of SABAs, and to some extent they have. The protective period of a LABA is two to three times longer in duration than that of a SABA. However, when a LABA is taken daily it is apparent that the duration of its protective effect is reduced and there is a risk of EIA occurring well within the 12-hour administration schedules. Furthermore, daily use of LABAs attenuates the bronchodilator effect of SABAs, an effect that is greater the more severe the bronchoconstriction. This 'tolerance' increases both the time and the amount of therapy that is needed to recover from bronchoconstriction, and thus, could potentially impact on the success of rescue therapy should severe EIA occur. The daily use of LABAs also increases the sensitivity of the bronchial smooth muscle to contractile agents. This increase in sensitivity is almost equivalent to the extent to which inhaled corticosteroids reduce sensitivity to the same contractile agents. The increased sensitivity to contractile agents may occur either by a reduction in the inhibitory effect of beta(2)-adrenoceptor agonists on release of mediators from mast cells or by a direct effect on the bronchial smooth muscle. These unwanted effects of LABAs are not necessarily reduced by concomitant treatment with inhaled corticosteroids. As the number of children being treated with LABAs increases, it is predicted that problems with breakthrough EIA will also increase. We need to know the percentage of children taking a LABA daily who are requiring either extra doses of a beta(2)-adrenoceptor agonist to prevent (or reverse) EIA or other provocative stimuli. If this percentage is significant then we may need to reconsider the position of LABAs in the treatment of children with asthma who regularly perform strenuous physical activity.

The effect of varying tonicity on nasal epithelial ion transport in cystic fibrosis

There is reasonable evidence that the fluid layer of the airway epithelium is exposed to changes in tonicity. The inspiration of cool, dry air causes an increased tonicity, whereas this tonicity may be decreased by glandular secretions. We hypothesized that the cystic fibrosis transmembrane conductance regulator (CFTR) is involved in the responses to changes in tonicity and that these may be altered in cystic fibrosis (CF). Using nasal potential difference (PD) protocols in 8 subjects with CF and 10 subjects without CF, we investigated the effects of hyper- and hypotonicity on ion transport processes. We found significant differences between the two groups. In response to a hypertonic challenge (mannitol 500 mM), there was a decreased PD in both groups, suggesting decreased sodium absorption. However, after the prior inhibition of sodium transport using amiloride, there was an increased PD in the non-CF group alone, suggesting CFTR-mediated chloride secretion in response to luminal hypertonicity. For the hypotonic solution, we found that hypotonicity inhibited CFTR-mediated chloride secretion in the non-CF group. These data suggest that CFTR plays a role in the recognition and regulation of airway fluid tonicity.

Oral breathing challenge in participants with vocal attrition

Vocal folds undergo osmotic challenge by mouth breathing during singing, exercising, and loud speaking. Just 15 min of obligatory oral breathing, to dry the vocal folds, increases phonation threshold pressure (Pth) and expiratory vocal effort in healthy speakers (M. Sivasankar & K. Fisher, 2002). We questioned whether oral breathing is more detrimental to phonation in healthy participants with a history of temporary vocal attrition. The effects of a 15-min oral or nasal breathing challenge on Pth and perceived expiratory vocal effort were compared for participants reporting symptoms of vocal attrition (N = 18, ages 19-38 years) and normal controls (N = 20, ages 19-33 years). Post-challenge-prechallenge differences in Pth (deltaPth) and effort (deltaEffort) revealed that oral breathing, but not nasal breathing, increased Pth (p < .001 ) and effort (p < .001) at low, comfortable, and high pitch. deltaPth was significantly greater in participants with vocal attrition than in normal controls (p < .001). Nasal breathing reduced Pth for all controls but not for all participants reporting vocal attrition. deltaPth was significantly and linearly correlated with deltaEffort (rvocal attrition = .81, p < .001; rcontrol = .84, p < .001). We speculate that the greater increases in Pth in participants reporting vocal attrition may result from delayed or inadequate compensatory response to superficial laryngeal dehydration. Obligatory oral breathing may place voice users at risk for exacerbating vocal attrition. That sol layer depletion by obligatory oral breathing increased Pth and vocal effort provides support for the role of superficial hydration in maintaining ease of phonation.

Release of inflammatory mediators from eosinophils following a hyperosmolar stimulus

Airway dehydration and subsequent hyperosmolarity of periciliary fluid are considered critical events in exercise-induced bronchoconstriction (EIB). It has been shown that an in vitro hyperosmolar stimulation of basophils and mast cells with mannitol can induce the release of histamine and leukotrienes. The aim of this study was to establish if a hyperosmolar challenge could trigger activation of eosinophils to release chemokines and lipid mediators. Peripheral blood eosinophils were isolated from seven asthmatic and six non-asthmatic subjects. Hyperosmolar stimulation of eosinophils with mannitol (0.7 M), resulted in a significant increase in LTC4 levels compared to baseline in both asthmatic (15.2+/-4.6 vs. 70.1+/-9.5; P = 0.0002) and control subjects (14.3+/-4.0 vs. 55.6+/-5.6; P = 0.0001). ECP levels did not increase significantly above baseline following mannitol stimulation in either group. This study shows that eosinophils can be activated by a hyperosmolar stimulus. Therefore it seems reasonable to suggest that eosinophils could contribute to EIB.

Beta-adrenergic agonists inhibit corticosteroid-induced apoptosis of airway epithelial cells

Airway epithelial damage is a feature of persistent asthma. Treatment with inhaled and oral corticosteroids may suppress inflammation and gain clinical control despite continued epithelial damage. We have previously demonstrated that corticosteroids elicit apoptosis of airway epithelial cells in culture. beta-Adrenergic receptor agonists are commonly used in asthma therapy and can inhibit corticosteroid-induced apoptosis of eosinophils. We tested the hypothesis that beta-adrenergic agonists would inhibit corticosteroid-induced airway epithelial cell apoptosis in cultured primary airway epithelial cells and in the cell line 1HAEo-. Albuterol treatment inhibited dexamethasone-induced apoptosis completely but did not inhibit apoptosis induced by Fas receptor activation. The protective effect of albuterol was duplicated by two different analogs of protein kinase A. The protective effect was not associated with increased translocation of the glucocorticoid receptor to the nucleus nor with changes in glucocorticoid receptor-mediated transcriptional activation or repression. We demonstrate that beta-adrenergic agonists can inhibit corticosteroid-induced apoptosis but not apoptosis induced by Fas activation. These data suggest that one potential deleterious effect of corticosteroid therapy in asthma can be prevented by concomitant beta-adrenergic agonist treatment.

Corticosteroid-induced apoptosis of airway epithelium: a potential mechanism for chronic airway epithelial damage in asthma

Damage to the airway epithelium is one prominent feature of chronic asthma. Mucosal damage includes gap openings, partial denudation, and loss of ciliated cells. Apoptosis of the airway epithelium is increasingly recognized as a potential mechanism by which damage may occur. Corticosteroids (CSs) induce apoptosis in inflammatory cells, which in part explains their ability to suppress airway inflammation. However, CS therapy does not necessarily reverse epithelial damage. We examined whether CS therapy actually could induce airway epithelial apoptosis using culture models of primary airway epithelial cells and cell lines. The administration of CSs in low-micromolar concentrations induces apoptosis that involves the disruption of mitochondrial polarity, the activation of caspases, and the involvement of Bcl-2. Clear differences exist between CS-induced apoptosis in the cultured epithelium vs cultured hematopoietic cells in regard to time course and resistance to apoptosis. Our data suggest that the use of CSs, in concentrations that could be attained in vivo with the inhalation of potent preparations or with systemic administration, may be one factor in the airways remodeling and epithelial damage that is seen in many patients with chronic, persistent asthma.

Airway dehydration: a therapeutic target in asthma?

BACKGROUND

Airway dehydration triggers exercise-induced bronchoconstriction in virtually all patients with active asthma. We are not aware of any investigations of airway dehydration in patients with naturally occurring asthma exacerbations. We wish to investigate whether airway dehydration occurs in acute asthmatic patients in the emergency department, and its functional significance.

METHODS

In a pilot study on 10 asthmatic patients and 10 control subjects in the emergency department, respiratory rate was counted manually, and relative humidity of expired air was recorded using an air probe hygrometer. In parallel laboratory studies carried out over 2 consecutive days, 19 asthmatics and 10 control subjects were challenged initially with dry air, and on the second day with humidified air. FEV(1) and humidity measurements were made immediately before and after the tachypnea challenges.

RESULTS

In the emergency department, the asthmatic group was more tachypneic (p < 0.0001) and their expired air was drier (p < 0.0001) than the control group. Following a dry-air tachypnea challenge in the laboratory, which caused dehydration of the expired air in all subjects, half of the asthmatics, but none of the control subjects, demonstrated a fall of > 10% in FEV(1) from baseline. This bronchoconstriction was prevented by humidifying the inspired air; tachypnea with no water loss did not affect lung function in asthmatic subjects.

CONCLUSIONS

Dehydration of the expired air is present in asthmatic patients in the emergency department. The bronchoconstriction triggered by dry-air tachypnea challenge in the laboratory can be prevented by humidifying the inspired air. Airway rehydration merits further investigation as a potential adjunct to acute treatment of asthma exacerbations.

Oral breathing increases Pth and vocal effort by superficial drying of vocal fold mucosa

Oral breathing superficially dehydrates the airway lumen by decreasing the depth of the sol layer in humans and animals. Conversely, nasal breathing can increase the humidity of inspired air. We compared the effects of short-term oral and nasal breathing on Pth and perceived vocal effort in 20 female subjects randomly assigned to two groups: oral breathing (N = 10, age 21-32 years); nasal breathing (N = 10, age 20-36 years). We hypothesized that short-term oral breathing, but not nasal breathing, would increase Pth, and that subjects would perceive this change as an increase in vocal effort. Following 15 minutes of oral breathing, Pth increased at comfortable and low pitch (p < 0.01) with 6 of 10 subjects reporting increased vocal effort. Nasal breathing reduced Pth at all three pitches (p < 0.01), and 7 of 10 subjects reported decreased vocal effort. Over all subjects, 49% of the variance in treatment-induced change in Pth was accounted for by change in vocal effort (R = 0.70). We posit that obligatory oral breathing places healthy subjects at risk for symptoms of increased vocal effort. The facilitatory role of superficial hydration on vocal fold oscillation should be considered in biomechanical models of phonation and in the clinical prevention of laryngeal dryness.

Apoptosis of airway epithelial cells induced by corticosteroids

Damage to the airway epithelium is one prominent feature of chronic asthma. Corticosteroids induce apoptosis in inflammatory cells, which in part explains their ability to suppress airway inflammation. However, corticosteroid therapy does not necessarily reverse epithelial damage. We hypothesized that corticosteroids may induce airway epithelial cell apoptosis as one potential explanation for persistent damage. We tested this hypothesis in cultured primary central airway epithelial cells and in the cell line 1HAEo(-). Treatment with dexamethasone, beclomethasone, budesonide, or triamcinolone each elicited a time-dependent and concentration-dependent cell death. This cell death was associated with cleavage of nuclear chromatin, mitochondrial depolarization, cytochrome c extrusion, activation of caspase-9, and expression of phosphatidylserine on the outer cell membrane. Inhibitors of caspase activity blocked apoptotic cell death, as did overexpression of the apoptosis regulators Bcl-2 or Bcl-x(L). We demonstrated that CD95 ligation is not essential for the corticosteroid-induced apoptosis in airway epithelial cells. These data demonstrate that corticosteroids induce apoptotic cell death of airway epithelium. This raises the possibility that at least one of the major components of chronic airway damage in asthma, epithelial shedding and denudation, may in part result from a major therapy for the disease.

The effects of carbon dioxide on exercise-induced asthma: an unlikely explanation for the effects of Buteyko breathing training

OBJECTIVES

To examine the effect of breathing 3% CO2 on exercise-induced asthma (EIA), as a raised airway CO2 level is suggested to mediate the effects of Buteyko breathing training (BBT).

DESIGN

Double-blind crossover study, using a standard laboratory-based exercise challenge, with EIA defined as a fall of 15% or greater in the forced expiratory volume in one second (FEV1) within 30 minutes of completing a standard exercise protocol.

SUBJECTS

10 adults with confirmed EIA.

INTERVENTION

Air enriched with 3% CO2 during and for 10 minutes after exercise.

OUTCOME MEASURES

Maximum percentage fall in FEV1 after exercise. Area under curve (AUC) of the decrease in FEV1 with time.

RESULTS

Mean maximum fall in FEV1 was similar: 19.9% with air, and 26.9% with 3% CO2 (P = 0.12). The mean AUC for the total 30-minute post-exercise period was 355 for air and 520 for 3% CO2 (P = 0.07). After discontinuing the 3% CO2 at 10 minutes after exercise, there was a further and sustained fall in FEV1. Mean AUC for the period 10-30 minutes post-exercise was significantly greater for CO2 than air (275 and 137, respectively [P = 0.02]). Mean minute ventilation was increased when subjects exercised breathing 3% CO2: 77.5 L/min for 3% CO2, compared with 68.7 L/min for air (P = 0.02).

CONCLUSION

Breathing 3% CO2 during exercise does not prevent EIA. The shape of the FEV1 response curve after 3% CO2 suggests that a greater degree of EIA (because of increased minute ventilation during exercise) was opposed by a direct relaxant effect of CO2 on the airway. Increased airway CO2 alone is an unlikely mechanism for the reported benefits of BBT; nevertheless, further study of the effects of voluntary hypoventilation in asthma is warranted.

Hypertonic saline aerosol increases airway reactivity in the canine lung periphery

Hyperventilation with dry air increases airway surface fluid (ASF) osmolality and causes acute mucosal injury, leukocyte infiltration, and delayed airway obstruction and hyperreactivity in canine peripheral airways. The purpose of this study was to determine whether ASF hypertonicity per se can account for these hyperventilation-associated effects. We first measured ASF osmolality before and after normal (NSC) and hypertonic (HSC) saline aerosol challenges to document the magnitude of hypertonicity produced by these stimuli. We then measured canine peripheral airway resistance and reactivity to hypocapnia and aerosolized histamine before and after NSC and HSC. Cells and eicosanoid mediators recovered in bronchoalveolar lavage fluid at 5 and 24 h after NSC and HSC were examined. We found that HSC but not NSC caused acute ASF hyperosmolality, increased mediator release, and delayed airway hyperreactivity in the absence of mucosal injury and leukocyte infiltration. These observations suggest that ASF hyperosmolality contributes to the development of the late-phase response to hyperventilation and further suggest that hyperventilation-induced mucosal injury independently initiates leukocyte infiltration and late-phase airway obstruction.

Pulmonary capillary blood volume in hyperpnea-induced bronchospasm

Reactive hyperemia of the bronchial circulation has been postulated to contribute to the airway narrowing that occurs following exercise or hyperpnea in subjects with asthma with hyperpnea-induced bronchospasm (HIB). Changes in lung parenchymal mechanics also occur in HIB, including increases in peripheral airway resistance. Since the peripheral airways and lung parenchyma are supplied by the pulmonary circulation, and changes in the pulmonary circulation could alter airway resistance or tissue mechanics, we hypothesized that pulmonary capillary blood flow would increase in association with HIB, resulting in increases in pulmonary capillary blood volume (VC). We measured VC by using two test gases of varying oxygen concentration to determine the diffusing capacity of the lung for carbon monoxide (DL(CO)) before and after a period of hyperpnea in 13 subjects with asthma with HIB and 10 control subjects without asthma. Despite subjects with asthma having a significant fall in FEV(1) following hyperpnea compared with control subjects (DeltaFEV(1) = -26 +/- 12 versus -4 +/- 4%, mean +/- SD, p < 0.001), there was no change in the DL(CO) or VC from baseline values. We conclude that pulmonary capillary blood volume does not change following hyperpnea, and therefore that changes in pulmonary blood flow are not associated with HIB.

The mechanism of exercise-induced asthma is

Exercise-induced asthma (EIA) refers to the transient narrowing of the airways that follows vigorous exercise. The mechanism whereby EIA occurs is thought to relate to the consequences of heating and humidifying large volumes of air during exercise. In 1978 airway cooling was identified as an important stimulus for EIA; however, severe EIA also occurred when hot dry air was inspired, and there was no abnormal cooling of the airways. In 1986 the thermal hypothesis proposed that cooling of the airways needed to be followed by rapid rewarming and that these two events caused a vasoconstriction and a reactive hyperemia of the bronchial microcirculation, together with edema of the airway wall, causing the airways to narrow after exercise. The osmotic, or airway-drying, hypothesis developed from 1982-1992 because neither airway cooling nor rewarming appeared to be necessary for EIA to occur. As water is evaporated from the airway surface liquid, it becomes hyperosmolar and provides an osmotic stimulus for water to move from any cell nearby, resulting in cell volume loss. It is proposed that the regulatory volume increase, after cell shrinkage, is the key event resulting in release of inflammatory mediators that cause airway smooth muscle to contract and the airways of asthmatic subjects to narrow. This event may or may not be associated with airway edema. The osmotic and thermal theories come together by considering that inspiration of cold air not only cools the airways but also increases the numbers of airway generations becoming dehydrated in the humidifying process.

Effects of cool, dry air stimulation on peripheral lung mechanics in asthma

We have previously demonstrated that peripheral airway resistance (Rp) rises more in asthmatics than in nonasthmatic control subjects after segmental challenge with cool, dry air. To better understand this rise in Rp, we used a stop-flow method to measure the decay of segment pressure with time that yielded information on airway resistance (Raw), final plateau pressure (Pp), and peripheral lung compliance (Cp). After stop-flow maneuvers in all seven asthmatics and all seven normal subjects, pressure decayed smoothly without an initial sudden drop. This finding suggests that Raw was negligible and that the predominant site of flow resistance was the collateral pathways of the obstructed segment. Asthmatics had a significantly higher Pp and lower Cp at baseline than did normal subjects, but neither Pp nor Cp changed after challenge. Pp and Rp were significantly correlated. When interpreted in terms of a single-compartment nonlinear model, we concluded that Rp is predominantly determined by the resistance of the collateral airways rather than the more proximal airways. We also concluded that, compared with normal subjects, asthmatics have (1) more collateral airway narrowing and closure and lower segmental compliance, and (2) after challenge, increased collateral airway narrowing or closure without a change in compliance of the distal lung parenchyma. These results reflect the fundamental differences in peripheral lung mechanics between asthmatic and nonasthmatic subjects and in their response to directly instilled cool, dry air.

Experimental models in asthma

Histamine is an important mediator released from activated mast cells in acute bronchoconstriction provoked by allergen, exercise, hypertonic stimuli and inhaled adenosine. Histamine may also contribute to the allergen-induced late asthmatic response probably following the recruitment and activation of basophils. H1-receptor antagonists partially attenuate these responses but greater inhibition when these drugs are combined with cysteinyl LT1-receptor antagonists indicative of an interaction between mast cell-derived mediators. The combination of two or more selective mediator antagonists in the treatment of allergic disorders such as asthma offers a new therapeutic approach worthy of careful appraisal.

Hyperventilation with dry air increases airway surface fluid osmolality in canine peripheral airways

Hyperventilation-induced bronchoconstriction (HIB) is a component of exercise-induced asthma (EIA) believed to result from the penetration of unconditioned air into the lung periphery. We used a canine model of EIA to examine the effect of hyperventilation on airway surface fluid (ASF) volume and osmolality, and to determine if the observed kinetics support the hypothesis that hyperventilation-induced changes in ASF osmolality initiate bronchoconstriction. Exposure of sublobar airways to dry air at baseline insufflation resulted in stable measurements of ASF volume, ASF osmolality, and peripheral airway resistance (Rp). Baseline insufflation of warm humidified air increased ASF volume, but did not alter ASF osmolality. Hyperventilation challenge with warm humidified air (WAC) increased Rp and ASF volume, but decreased ASF osmolality. Dry air challenge (DAC) increased Rp, ASF volume, and ASF osmolality. ASF osmolality during DAC was markedly higher when compared with posthyperventilation values. Post-DAC changes in (Delta) ASF volume and osmolality were poorly correlated with the development of HIB. In contrast to Delta ASF after DAC, Delta ASF osmolality during DAC was strongly correlated with HIB, and tended to be inversely related to Delta ASF volume. These observations are consistent with the hypothesis that changes in airway osmolality during hyperventilation initiate peripheral airway constriction.

Effects of swimming training on aerobic capacity and exercise induced bronchoconstriction in children with bronchial asthma

BACKGROUND

A study was undertaken to determine whether swimming training improved aerobic capacity, exercise induced bronchoconstriction (EIB), and bronchial responsiveness to inhaled histamine in children with asthma.

METHODS

Eight children with mild or moderate asthma participated in swimming training every day for six weeks. The intensity of training was individually determined and set at 125% of the child's lactate threshold (LT), measured using a swimming ergometer. Another group of eight asthmatic children served as control subjects. Aerobic capacity and the degree of EIB were assessed by both cycle ergometer and swimming ergometer before and after swimming training.

RESULTS

The mean (SD) aerobic capacity at LT increased by 0.26 (0.11) kp after training when assessed with the swimming ergometer and by 10.6 (4.5) W when assessed with the cycle ergometer, and these changes were significantly different from the control group. The mean (SD) maximum % fall in forced expiratory volume in one second (FEV1) to an exercise challenge (cycle ergometer) set at 175% of LT decreased from 38.7 (15.4)% before training to 17.9 (17.6)% after training, but with no significant difference from the control group. There was, however, no difference in histamine responsiveness when compared before and after the training period.

CONCLUSION

A six week swimming training programme has a beneficial effect on aerobic capacity but not on histamine responsiveness in children with asthma.

Responsiveness to mannitol in asthmatic subjects with exercise- and hyperventilation-induced asthma

We investigated airway responsiveness to mannitol, a new hyperosmolar challenge, in persons hyperresponsive to airway drying. We studied 36 asthmatic subjects, 18 to 40 yr of age, responsive to exercise (n = 23) and eucapnic hyperventilation (n = 28) defined by a 10% fall in FEV1. Fifteen subjects performed both challenges. All subjects performed a challenge with dry powder mannitol, encapsulated and delivered via a Dinkihaler until a 15% decrease in FEV1 was documented or a cumulative dose of 635 mg was delivered. All subjects responsive to eucapnic hyperventilation and all but one subject responsive to exercise were responsive to mannitol. Sixty-nine percent of subjects had a positive response to mannitol after less than 155 mg (6 capsules) and 94% less than 320 mg (10 capsules). The provoking dose of mannitol required to cause a 15% fall in FEV1 (PD15) was related to the severity of the response to exercise (Pearson's correlation coefficient [rp] = 0.68, p < 0.01) and eucapnic hyperventilation (rp = 0.68, p < 0.01) in subjects who were not taking inhaled corticosteroids. The mean (+/- SD) maximum percent fall in FEV1 after mannitol was 24.4 +/- 6.2% and recovery to bronchodilator occurred within 10 min in most subjects. The mannitol test is simple, inexpensive, faster to perform than hyperpnea with dry air and could become an office-based test. Further studies are now required to determine the sensitivity of mannitol to identify exercise-induced asthma in a random population.

Increased urinary excretion of LTE4 after exercise and attenuation of exercise-induced bronchospasm by montelukast, a cysteinyl leukotriene receptor antagonist

BACKGROUND

A study was undertaken to determine whether montelukast, a new potent cysteinyl leukotriene receptor antagonist, attenuates exercise-induced bronchoconstriction. The relationship between the urinary excretion of LTE4 and exercise-induced bronchoconstriction was also investigated.

METHODS

Nineteen non-smoking asthmatic patients with a forced expiratory volume in one second (FEV1) of > or = 65% of the predicted value and a reproducible fall in FEV1 after exercise of at least 20% were enrolled. Subjects received placebo and montelukast 100 mg once daily in the evening or 50 mg twice daily, each for two days, in a three-period, randomised, double blind, crossover design. In the evening, approximately 20-24 hours after the once daily dose or 12 hours after the twice daily dose, a standardised exercise challenge was performed. Data from 14 patients were available for complete analysis.

RESULTS

The mean (SD) maximal percentage decrease in FEV1 after exercise was 29.6 (16.0), 17.1 (8.2), and 14.0 (9.4) for placebo, once daily, and twice daily regimens, respectively. The mean (95% CI) percentage protection was 37 (15 to 59) for the group who received 50 mg twice daily and 50 (31 to 69) for those who received 100 mg once daily. Active treatments were not different from each other. The mean (SD) plasma concentrations of montelukast were higher after the twice daily regimen (1.27 (0.81) microgram/ml) than after the once daily regimen (0.12 (0.09) microgram/ml); there was no correlation between the percentage protection against exercise-induced bronchoconstriction and plasma concentrations. After exercise urinary excretion of LTE4 increased significantly during placebo treatment (from 34.3 to 73.7 pg/mg creatinine; p < 0.05) but did not correlate with the extent of exercise-induced bronchoconstriction.

CONCLUSIONS

Montelukast protects similarly against exercise-induced bronchoconstriction between plasma concentrations of 0.12 and 1.27 micrograms/ml. The increase in the urinary excretion of LTE4 after exercise and the protection from exercise-induced bronchoconstriction with a cysteinyl leukotriene receptor antagonist provide further evidence of the role of leukotrienes in the pathogenesis of exercise-induced bronchoconstriction.

Roles of hydration, sodium, and chloride in regulation of canine mucociliary transport system

To gain insight into the homeostatic mechanisms regulating airway ion/water fluxes and mucociliary transport, the canine tracheobronchial airway fluid was perturbed by deposition of hypo- and hyperosmotic aerosols for >1 h. Tracheal ciliary beat frequency (CBF) was measured by using heterodyne laser light scattering. Tracheal mucus velocity (TMV) and bronchial mucociliary clearance (BMC) were measured by using radioaerosols and nuclear imaging. Respiratory tract fluid output (RTFO) was collected by using a secretion-collecting endotracheal tube. In six dogs, CBF increased during water deposition in the airways to 180 +/- 30 mg/min and RTFO increased from 2.2 +/- 0.5 to 18.3 +/- 1.6 mg/min, accounting for <10% of the fluid deposition. TMV and BMC were unchanged. CBF, TMV, and BMC were markedly increased by inhalation of aerosolized 3.4 M NaCl. Aerosolized 0.85 M NaCl, in contrast, decreased BMC. In this case, RTFO represented 24% of aerosol deposition. Aerosolized 0.85 M choline chloride and 0.85 M sodium gluconate enhanced BMC and TMV concurrent with a decrease in CBF. RTFO of sodium gluconate studies exceeded 50% of aerosol deposition. Thus the airways appear to have transepithelial compensatory mechanisms that reduce the impact of a moderate increases in NaCl and hydration load, but when these responses cannot adequately respond because of the delivery of impermeable ions or very high tonicity, removal of the challenges are affected by a stimulation of mucociliary transport.

Challenge tests to assess airway hyperresponsiveness and efficacy of drugs used in the treatment of asthma

Bronchial provocation tests are useful to diagnose and assess severity of asthma and to follow response to treatment. The tests used include those stimuli that act "directly" on receptors causing contraction of airway smooth muscle, e.g., pharmacological agents, and those stimuli that act "indirectly" by causing release of endogenous mediators that cause the airways to narrow. These "indirect" stimuli include physical ones such as airway drying from hyperpnea and changes in airway osmolarity from inhaling aerosols of water and hyperosmolar saline. Indirect stimuli cause the airways to narrow in response to endogenously released substances from inflammatory cells or nerves and responses are thought to reflect the presence and severity of inflammation of asthma. Challenge with hyperosmolar saline is now being used as an indirect test because it also identifies persons with exercise-induced asthma and is appropriate to assess suitability for diving with SCUBA. Hyperosmolar challenge is also useful to assess the effect of both the acute and chronic treatment with antiinflammatory drugs. This, combined with the potential to collect inflammatory cells in sputum induced by the same stimulus should result in this challenge being more widely used, not only in the hospital laboratory but also in epidemiology and occupational asthma.

Eucapnic voluntary hyperventilation as a bronchoprovocation technique: development of a standarized dosing schedule in asthmatics

A variety of dosing schedules have been reported for the hyperventilation method of broncho-provocation testing. To evaluate the effect of challenge technique on the bronchoconstrictive response, we had 16 subjects perform eucapnic voluntary hyperventilation (EVH) with dry, room temperature gas using four different dosing schedules. The hyperventilation challenge dosages included the following: (1) a target minute ventilation (VE) of 20 x FEV1 for 6 min; (2) a target VE of 15 x FEV1 for 12 min; (3) an interrupted challenge with a target VE of 30 x FEV1 for 2 min repeated 3 times; and (4) a target VE of 30 x FEV1 for 6 min. Challenges 2, 3, and 4 gave identical absolute ventilatory challenges (identical factor FEV1 x minutes) but at different VE dosages or time. Challenges 1 and 4 were of identical length, but different target VE. The mean postchallenge fall in FEV1 was 16.6 +/- 10.9%, 11.0 +/- 8.1%, 19.6 +/- 9.9%, and 26.7 +/- 11.3% for challenges 1, 2, 3, and 4, respectively. The response to an identical EVH challenge (FEV1 x 30 for 6 min) was reproducible when performed on separate days. We conclude that the challenge technique used for hyperventilation testing will have a significant impact on the bronchoconstrictive response and must be taken into account when interpreting study results. Tests may be quantitatively comparable over a narrow range of challenge time and VE. We recommend that a 6-min uninterrupted EVH challenge using dry, room temperature gas at a target VE of 30 x FEV1 be adopted as the "standard" challenge.

The refractory period after eucapnic voluntary hyperventilation challenge and its effect on challenge technique

To evaluate whether there is a refractory period (RP) after hyperventilation challenge, we compared the bronchoconstrictive response to repetitive eucapnic voluntary hyperventilation challenge with dry, room temperature air (EVH). The serial challenges were identical with 11 known asthmatics hyperventilating for 6 min at a target minute ventilation of 30 times their FEV1 measured before either challenge. There was a significant difference between the mean postchallenge fall in FEV1 to the initial EVH challenge (27.4 +/- 9.8%) and the response to the second EVH challenge (16.1 +/- 5.9%) (p = 0.0001), indicating refractoriness. We then evaluated whether 6 min of uninterrupted EVH challenge gives a similar bronchospastic response to that which results from an equivalent (by total minute ventilation) interrupted challenge of 2 min of EVH repeated three times. The mean post-challenge fall in FEV1 in response to this interrupted challenge was 18.9 +/- 10.6%, which was significantly different from the 27.4% fall in response to 6 consecutive minutes of EVH (p = 0.036). This study demonstrates that there is a refractory period after repeated EVH challenges and this refractoriness affects the response to interrupted, or dosed, EVH challenge.

Selective response of human airway epithelia to luminal but not serosal solution hypertonicity. Possible role for proximal airway epithelia as an osmolality transducer

The response of cultured human nasal epithelia to hypertonic bathing solutions was tested using ion-selective microelectrode and quantitative microscopy. Raised luminal, but not serosal, osmolality (+/- 150 mM mannitol) decreased Na+ absorption but did not induce Cl- secretion. Raised luminal osmolality increased cell Cl- activity, Na+ activity, and transepithelial resistance and decreased both apical and basolateral membrane potentials and the fractional resistance of the apical membrane; equivalent circuit analysis revealed increases in apical, basolateral, and shunt resistances. Prolonged exposure (10 min) to 430 mosM luminal solution elicited no regulation of any parameter. Optical measurements revealed a reduction in the thickness of preparations only in response to luminal hypertonic solutions. We conclude that (a) airway epithelial cells exhibit asymmetric water transport properties, with the apical membrane water permeability exceeding that of the basolateral membrane; (b) the cellular response to volume loss is a deactivation of the basolateral membrane K+ conductance and the apical membrane Cl- conductance; (c) luminal hypertonicity slows the rate of Na+ absorption but does not induce Cl- secretion; and (d) cell volume loss increases the resistance of the paracellular path. We speculate that these properties configure human nasal epithelium to behave as an osmotic sensor, transducing information about luminal solutions to the airway wall.

Water loss without heat flux in exercise-induced bronchospasm

We identified inspired gas conditions that result in no net respiratory heat loss, an isenthalpic condition, but induce a mucosal loss of water. Inspired gas at 37 degrees C with 47 mm Hg water vapor pressure, 56 degrees C with 38 mm Hg; and 78 degrees C with 27 mm Hg has the same heat content as fully saturated air at body temperature. In four normal subjects hyperventilating at a minute ventilation of 30 times their FEV1 for 6 min, expired temperatures at the mouth averaged 39 degrees, 43 degrees, and 43 degrees C for the three conditions. Retrotracheal esophageal temperatures did not fall in any subject, thereby demonstrating the absence of significant airway cooling. Nine subjects with exercise-induced bronchospasm were tested under the same conditions. Baseline functions showed an FEV1 of 85 +/- 10% of predicted (mean +/- SD), FVC, 98 +/- 13% of predicted, and FEV1/FVC, 79 +/- 4% of predicted. The asthmatic subjects demonstrated postchallenge mean falls in FEV1 of 3.4%, 6.2%, and 10.1% for the three conditions, with bronchospasm increasing as the temperature of the inspired air increased (p = 0.001). The amount of respiratory water lost from the respiratory mucosa significantly correlated with the resultant bronchospastic response as measured by the fall in FEV1 (p = 0.017), but the net respiratory heat lost did not significantly correlate (p = 0.113). This study demonstrates that bronchospasm can be induced without significant respiratory heat loss or airway cooling and suggests that it is proportional to the amount of water lost from mucosal surfaces.

The airway microvasculature and exercise induced asthma

It has been proposed that exercise induced asthma is a result of "rapid expansion of the blood volume of peribronchial plexi" (McFadden ER, Lancet 1990;335:880-3). This hypothesis proposes that the development of exercise induced asthma depends on the thermal gradient in the airways at the end of hyperpnoea. The events that result in exercise induced asthma are vasoconstriction and airway cooling followed by reactive hyperaemia. We agree that the airway microcirculation has the potential for contributing to the pathophysiology of exercise induced asthma. We do, however, question whether reactive hyperaemia, in response to airway cooling, is the mechanism whereby hyperpnoea provokes airways obstruction in asthmatic patients. Further, we question whether vasoconstriction accompanies dry air breathing and whether an abnormal temperature gradient and rapid rewarming of the airways are prerequisites for exercise induced asthma. From published experiments we conclude that dry air breathing is associated with vasodilation and increase in airway blood flow rather than vasoconstriction and a decrease in blood flow to the airways. We propose that the stimulus for the increase in airway blood flow is an increase in osmolarity of the airway submucosa. This osmotic change is caused by the movement of water to the airway lumen in response to evaporative water loss during hyperpnoea. The increase in airway blood flow may occur directly or indirectly by the osmotic release of mediators. Exercise induced asthma is most likely to be due to the contraction of bronchial smooth muscle caused by the same mediators. Whether it is enhanced or inhibited by alterations in airway blood flow is not yet established in man.

Attenuation of exercise induced asthma by local hyperthermia

BACKGROUND

Prior treatment with local hyperthermia has been shown to prevent mast cell degranulation and leucocyte histamine release, and to reduce mortality and cellular infiltrates in a model of acute lung injury. Local hyperthermia is effective in reducing the symptoms of the common cold and perennial and seasonal allergic rhinitis, nasal patency also being improved in rhinitis. It is possible that these effects are mediated by common anti-inflammatory mechanisms, and that this treatment may be effective in the treatment of asthma. The effect of prior local hyperthermia on the response to exercise challenge and histamine bronchoprovocation was therefore examined.

METHODS

In a randomised, double blind, placebo controlled, crossover study, 10 asthmatic subjects with exercise induced asthma used machines delivering 40 1/minute of fully humidified air at either 42 degrees C (active treatment) or 31 degrees C (placebo treatment) for 30 minutes' tidal breathing. For each pretreatment, at two week intervals they underwent exercise challenges starting one and 24 hours after starting the inhalations. After a further two weeks the protocol was repeated with histamine substituted for the exercise challenges.

RESULTS

The mean (SE) maximum percentage fall in forced expiratory volume in one second (FEV1) was significantly lower one hour after treatment with air at 42 degrees C (30.8% (3.1%)) than after treatment with air at 31 degrees C (22.3% (2.9%)). There was no significant effect on exercise challenge at 24 hours, or on histamine challenge at either time point, though there were nonsignificant trends towards protection with exercise at 24 hours and with histamine at one hour.

CONCLUSION

In asthmatic subjects the response to exercise challenge is significantly attenuated one hour after treatment with local hyperthermia. This treatment warrants further investigation in the treatment of clinical asthma and other inflammatory disorders.

Duration of protection by inhaled salmeterol in exercise-induced asthma

Beta-adrenoceptor agonists such as albuterol are very effective in preventing exercise-induced asthma (EIA) when they are given as an aerosol immediately before exercise. However, their duration of protection against EIA is usually less than 2 h. This may be due partly to their rapid clearance from the airways. Salmeterol is a highly lipophylic compound that is thought to bind to an exoreceptor near the beta-receptor. The objective of this study was to compare the protective effect of salmeterol with albuterol against EIA. Exercise was performed 0.5, 2.5, 4.5, and 6.5 hours after administration of the active drugs. Subjects attended the laboratory on four days within six weeks and cycled for 8 min breathing dry compressed air. We studied 17 asthmatic subjects (aged 19 to 49 years) with moderate to severe EIA. Salmeterol (50 micrograms) or albuterol (200 micrograms) was given from a metered dose inhaler via a spacer (Volumatic). On the control day, the mean work load +/- 1 SD was 174 +/- 47 W, ventilation (VE) was 77.9 percent +/- 11.2 percent of the target ventilation (60 percent maximum voluntary ventilation [MVV]), and heart rate was 170 +/- 14 beats per minute. This intensity was maintained for all tests. FEV1 was measured before and after exercise and was expressed as percent predicted and as percentage of the preexercise value (percentage of fall). Thirty minutes after treatment, both drugs were effective in inhibiting EIA--percentage of fall in FEV1, 17 +/- 12 after salmeterol; percentage of fall in FEV1, 15 +/- 15 after albuterol. At 2.5, 4.5, and 6.5 hours, the reduction in FEV1 was significantly less (p less than 0.01) after salmeterol compared with albuterol. At 6.5 hours, the percentage of fall in FEV1 was 20 +/- 10 after salmeterol and 36 +/- 12 after albuterol. Salmeterol also had a more prolonged action as a bronchodilator and values for FEV1 were significantly higher compared with those on albuterol at 4.5 and 6.5 hours. At 6.5 hours, the FEV1 percent predicted was 96 +/- 10 after salmeterol and 84 +/- 12 after albuterol (p less than 0.01). We conclude that the extent of protection against EIA and the bronchodilation induced by both drugs was similar, but that salmeterol has a longer duration of action compared with albuterol. The reason for its superior duration of action may be due to a slower clearance of the drug from the airways.

Exercise but not methacholine differentiates asthma from chronic lung disease in children

Bronchial provocation challenges with exercise and methacholine were performed on the same day or within a short interval in 52 children with asthma, 22 with other types of chronic lung disease (including cystic fibrosis), and 19 control subjects with no evidence of chronic lung disease. There were no significant differences in the baseline lung function before the two types of challenge in the individual groups and differences between the patients with asthma and with chronic lung disease were minor. When the mean -2 SD of the methacholine response of the control group was taken as the lower limit of normal, 49/52 (94%) patients with asthma and 18/22 (82%) with chronic lung disease responded abnormally. In contrast, with the mean +2 SD of the exercise response of the control group as the upper limit of normal, 41/52 (79%) asthmatic patients responded but none of those with chronic lung disease. Thus the response to the two types of challenge helps to distinguish asthma from other types of chronic lung disease in children.