Upper respiratory tract infections and airway reactivity in normal and asthmatic subjects

Longitudinal study of free running exercise challenge: reproducibility

The reproducibility of free running exercise challenge has been examined in an unselected population of 8-10 year olds. Using a standardised protocol, monthly exercise tests were performed on 143 children over one year. A positive test was defined using both a 15% and 20% fall in peak expiratory flow after exercise. The mean (95% confidence interval, CI) population frequency for a positive test at 15% fall was 14.9% (6.5 to 23.3) and coefficient of variation 24.6%. For a 20% fall, the mean (95% CI) population frequency was 7.9% (2.9 to 12.9) and coefficient of variation 27.8%. Seventy two (50.3%) of the children gave at least one positive response at 15% fall. Exercise testing is not reproducible in the community setting and should not be used as a screening test. Exercise data from epidemiological studies of asthma should be interpreted with caution.

Viruses as precipitants of asthma symptoms. II. Physiology and mechanisms

The upper and lower airways have complimentary roles in the ultimate object of supplying the body with oxygen whilst removing waste products of metabolism. Pathology in one area may trigger a response in another, the physiology of which, in the case of virus-induced asthma exacerbations remains poorly characterized. Viral infection of the upper airways by common cold viruses frequently triggers a response in the lower airways leading to prolonged morbidity, especially in subjects with significant pre-existing airway disease. The induction or amplification of BHR may be an important mechanism whereby asthmatic symptoms are produced although the cellular and tissue events or reflex mechanisms activated by viral illnesses and underlying BHR changes are poorly defined and may be dependent on the type and the severity of infection. Children and asthmatics tend to develop frequent colds setting in motion a sequence of events culminating in airway obstruction and symptoms of wheezing, coughing and chest tightness. This may reflect independent inflammatory changes caused by a simply additive effect of viral damage to the mucosa superimposed upon pre-existing allergic inflammation (Fig. 1). Few if any symptoms will develop in normal subjects with a mild cold whereas significant symptoms may ensue if the cold is severe and induces marked lower airway swelling, secretions and smooth muscle contraction; pathology to which children who have small calibre airways may be particularly susceptible. In asthmatics even a mild cold frequently induces exacerbation of symptoms, while serious life-threatening asthma attacks may occur associated with a severe cold. Some studies have suggested that this effect is not only additive but also synergistic and brought about by release of the mediators already present in increased quantities, the induction of IgE synthesis, or by the potentiation of neural and epithelial damage. The combined effect of both asthma and viruses may thus be amplified and result in a sustained and refractory period of airway obstruction, severe symptoms and unstable asthma. As most hospital admissions for asthma occur over the winter months and soon after the start of the school terms [115], spread of viruses through the community to susceptible individuals may be the single most important cause of sustained exacerbations of asthma. Definition of the pathological and physiological mechanisms involved will lead to better understanding and may thus provide a basis for prevention and the development of effective forms of treatment for virus-induced asthma.

Acute bronchitis in the community: clinical features, infective factors, changes in pulmonary function and bronchial reactivity to histamine

A descriptive study of acute bronchitis in patients without pre-existing pulmonary disease was undertaken in the community during the winter months of 1986-87. Forty-two episodes were investigated in 40 individuals. The cardinal symptom was the acute onset of cough (100%), usually productive (90%). Wheezing was noted by 62% of patients, but heard on auscultation in only 31%. A potential pathogen was isolated in 29% of cases with a virus (eight cases) being identified more frequently than either Mycoplasma pneumoniae (three cases) or a bacterium (three cases). The acute illness was associated with significant reductions in forced expired volume in 1 second (P less than 0.02) and peak expiratory flow (P less than 0.001) but not forced vital capacity compared to 6 weeks later. Ten of the 27 (37%) patients who had a histamine challenge test performed at 6 weeks had a PD20 of less than 7.8 mumol histamine. Thirty-nine episodes (93%) were treated with antibiotics by the general practitioner, the clinical course being unremarkable apart from one patient who developed a lingular pneumonia despite antibiotic therapy. Further studies are required to assess whether acute bronchitis causes an acute increase in bronchial hyperresponsiveness and whether either antibiotics or inhaled bronchodilators or anti-inflammatory therapy has a useful role in the management of this predominantly viral illness.

The effect of intranasal nedocromil sodium on viral upper respiratory tract infections in human volunteers

Two studies involving double-blind group comparative trials in human volunteers compared the effects of intranasal nedocromil sodium (2.6 mg active drug per nostril, q.i.d.) with placebo on clinical symptoms and performance impairment associated with the common cold. In the first study volunteers were challenged with rhinoviruses (RV9 and RV14), and in the second study with respiratory coronavirus. In both studies, active and placebo groups of volunteers were demographically similar. Infection rates in both groups were also similar. There were no withdrawals resulting from unusual symptoms related to either treatment. In the rhinovirus study (19, placebo; 20, nedocromil sodium) daily symptom scores and daily mean nasal secretion weights were significantly lower in the nedocromil sodium-treated group. In the coronavirus study (26, placebo; 27, nedocromil sodium) there was little difference in the severity of colds between the active and placebo-treated groups, but trends favoured nedocromil sodium. In both studies the impairment of performance in volunteers who developed a cold was significantly less in those treated with nedocromil sodium than in those treated with placebo.

Epidemiology of bronchial hyperresponsiveness

Asthma is a serious health problem, with both mortality and severity increasing in developed countries (55-57). The development of more specific tests to measure the prevalence and incidence of asthma is of paramount importance. Because measurement of BHR is the only practical objective method for assessing the abnormality of the airways in asthma, it is important to continue examining this measurement as a means of detecting asthma and to explore ways of increasing the sensitivity and specificity of the test. At present, it is clear that measurements of BHR in the community cannot be used as a marker of asthma and that the test requires careful interpretation, especially in adult populations. However, it is becoming apparent that moderate and severe levels of BHR (PD20FEV1 less than 0.8 mumol of histamine) are almost always associated with clinically important morbidity, and comparison of this BHR severity in populations may yield more information than comparison of a wider range of severity in which the associated factors are not well-defined. It is important to determine whether this range of severity of BHR is associated with long-term morbidity from asthma, and whether the use of other measurements from the dose-response curve, such as the shape or similarity of curves to different provoking agents, can increase the specificity of the test. It is also important to continue to investigate the risk factors associated with the development and occurrence of BHR so that individuals who are likely to develop BHR can be identified and, in the longer term, preventive measures can be introduced. There have been relatively few studies of the prevalence of BHR in large populations of children and adults in North America. Such studies would provide essential comparative information about apparent regional differences in both the prevalence of and the mortality from asthma.

Ethnic differences in prevalence of asthma symptoms and bronchial hyperresponsiveness in New Zealand schoolchildren

Maoris and Pacific Islanders in New Zealand have a higher asthma mortality and hospital admission rates than Europeans. To determine whether difference in asthma prevalence is the major factor underlying these differences in mortality, 2053 Auckland children aged 7-10 years (European 1084, Maori 509, Pacific Islander 460) were randomly sampled from school classes in the Auckland Urban Area, and studied by questionnaire (completed by parents) and histamine inhalation challenge to assess the provocative dose of histamine causing a 20% fall in FEV1 (PD20). Maoris had the highest prevalence rates of respiratory symptoms, and Europeans had rates similar to Pacific Islanders. For "any current wheeze" for example, the prevalence in Maoris was 22.2% compared with 16.1% and 16.3% in the Europeans and Pacific Islanders. The prevalence of diagnosed asthma was similar in the three groups. When bronchial hyperresponsiveness (defined as a PD20 less than or equal to 7.8 mumol histamine) was considered, Europeans had the highest rates (20%), followed by Maoris (13%), and then Pacific Islanders (8.7%). These differences were not accounted for by differences in socioeconomic status, rates of smoking in the home, age, gender, or height. It is concluded that differences in asthma prevalence do not satisfactorily explain the mortality and admission rate differences, although the higher symptom prevalence in the Maoris could be relevant to the higher mortality rate. Maori and Pacific Island children with symptoms of asthma were less likely to be taking prophylactic medication than European children. It is proposed that differences in management are important factors relevant to the increased mortality and morbidity from asthma in Polynesians.

Rhinovirus upper respiratory infection increases airway hyperreactivity and late asthmatic reactions

Although viral upper respiratory infections (URIs) provoke wheezing in many asthma patients, the effect of these illnesses on the airway response to inhaled antigen is not established. The following study evaluated the effect of an experimental rhinovirus (RV) illness on airway reactivity and response to antigen in 10 adult ragweed allergic rhinitis patients. Preinfection studies included measurements of airway reactivity to histamine and ragweed antigen. Furthermore, the patients were also evaluated for late asthmatic reactions (LARs) to antigen (a 15% decrease in forced expiratory volume of the first second approximately 6 h after antigen challenge). 1 mo after baseline studies, the patients were intranasally inoculated with live RV16. All 10 patients were infected as evidenced by rhinovirus recovery in nasal washings and respiratory symptoms. Baseline FEV1 values were stable throughout the study. During the acute RV illness, there was a significant increase in airway reactivity to both histamine and ragweed antigen (P = 0.019 and 0.014, respectively). Before RV inoculation, only 1 of the 10 subjects had an LAR after antigen challenge. However, during the acute RV illness, 8 of 10 patients had an LAR (P less than 0.0085 compared with baseline); the development of LARs was independent of changes in airway reactivity and the intensity of the immediate response to antigen. Therefore, we found that not only does a RV respiratory tract illness enhance airway reactivity, but it also predisposes the allergic patient to develop LARs, which may be an important factor in virus-induced bronchial hyperresponsiveness.

Descriptive epidemiology of bronchial reactivity in an adult population: results from a community study

The bronchial response to inhaled histamine has been suggested as an epidemiological tool for assessing the prevalence of asthma, though the exact relationship between reactivity and asthma is unknown. Tests of bronchial reactivity to histamine were carried out in 511 subjects aged 18-64 years, randomly selected from the population in two areas of the South of England, who had returned questionnaires on respiratory symptoms. Bronchial reactivity to less than or equal to 8 mumol histamine was present in 14% and was associated with positive skin test responses to common allergens and with smoking history. Both of these relationships were in turn dependent on age, skin sensitivity being the more important determinant of reactivity in the young and smoking the more important in older subjects. Bronchial reactivity was least prevalent in the 35-44 year age group. No independent effect on reactivity of sex, social class, or area of residence was detected, and no significant effect from recent respiratory tract infections. Interpretation of the bronchial response to histamine in selected groups of subjects must take account of age, atopic state, and smoking history.