The determinants of airway hyperresponsiveness to hypertonic saline in atopic asthma in vivo. Relationship with sub-populations of peripheral blood leucocytes

Sensory nerves and airway irritability

The lung, like many other organs, is innervated by a variety of sensory nerves and by nerves of the parasympathetic and sympathetic nervous systems that regulate the function of cells within the respiratory tract. Activation of sensory nerves by both mechanical and chemical stimuli elicits a number of defensive reflexes, including cough, altered breathing pattern, and altered autonomic drive, which are important for normal lung homeostasis. However, diseases that afflict the lung are associated with altered reflexes, resulting in a variety of symptoms, including increased cough, dyspnea, airways obstruction, and bronchial hyperresponsiveness. This review summarizes the current knowledge concerning the physiological role of different sensory nerve subtypes that innervate the lung, the factors which lead to their activation, and pharmacological approaches that have been used to interrogate the function of these nerves. This information may potentially facilitate the identification of novel drug targets for the treatment of respiratory disorders such as cough, asthma, and chronic obstructive pulmonary disease.

Bronchoprovocation testing

Airway smooth muscles of asthmatics tend to be hyperresponsive when provoked. The exaggerated bronchial constriction can be measured by the airflow limitation seen following bronchial provocation. Measuring bronchial hyperresponsiveness by broncho provocation testing is helpful in diagnosing and optimizing therapy. While numerous agents have been used to provoke a measurable airflow limitation, standardized protocols are available for only a few. This article aims to discuss the various methods that have been reported for bronchoprovocation testing.

Adenosine receptors and asthma

The pathophysiological processes underlying respiratory diseases like asthma are complex, resulting in an overwhelming choice of potential targets for the novel treatment of this disease. Despite this complexity, asthmatic subjects are uniquely sensitive to a range of substances like adenosine, thought to act indirectly to evoke changes in respiratory mechanics and in the underlying pathology, and thereby to offer novel insights into the pathophysiology of this disease. Adenosine is of particular interest because this substance is produced endogenously by many cells during hypoxia, stress, allergic stimulation, and exercise. Extracellular adenosine can be measured in significant concentrations within the airways; can be shown to activate adenosine receptor (AR) subtypes on lung resident cells and migrating inflammatory cells, thereby altering their function, and could therefore play a significant role in this disease. Many preclinical in vitro and in vivo studies have documented the roles of the various AR subtypes in regulating cell function and how they might have a beneficial impact in disease models. Agonists and antagonists of some of these receptor subtypes have been developed and have progressed to clinical studies in order to evaluate their potential as novel antiasthma drugs. In this chapter, we will highlight the roles of adenosine and AR subtypes in many of the characteristic features of asthma: airway obstruction, inflammation, bronchial hyperresponsiveness and remodeling. We will also discuss the merit of targeting each receptor subtype in the development of novel antiasthma drugs.

Sputum induction in severe asthma by a standardized protocol: predictors of excessive bronchoconstriction

Sputum induction is a noninvasive method to evaluate airway inflammation. We investigated whether it can be safely and successfully performed in patients with severe, difficult-to-control asthma, and whether the patients at risk can be identified. Ninety-three severe asthmatics were included, all symptomatic despite inhaled corticosteroids (> or = 1,600 microg/d) and long-acting beta(2)-agonists > 1 yr. Patients with a postbronchodilator FEV(1) < 1 L and < 50% predicted were excluded from participation. Sputum induction was performed according to a strict protocol, using 0.9%, 3.0%, and 4.5% NaCl inhalation. In 74% (CI: 64 to 83%) of patients an adequate sputum sample could be obtained. Twenty-two percent (CI: 14 to 33%) developed excessive bronchoconstriction (decrease in FEV(1) > 15% from baseline) despite the continuing use of long-acting bronchodilators and pretreatment with 400 microg salbutamol. The decrease in FEV(1) was associated with increased use of rescue short-acting beta(2)-agonists in the previous 2 d (r(s) = 0.51, p = 0.002), lower postbronchodilator FEV(1) (r(s) = -0.31, p = 0.004), and lower provocative concentration of histamine causing a 20% reduction in FEV(1) (PC(20)) (r(s) = -0.52, p < 0.001). Recent use of short-acting beta(2)-agonist increased the risk for excessive bronchoconstriction 10.2-fold (CI: 1.2 to 109.8). In conclusion, sputum induction can be safely and successfully performed in patients with severe, difficult-to-control asthma if a standardized protocol is used. However, severe bronchoconstriction may occur despite regular use of long-acting beta(2)-agonist and pretreatment with salbutamol 400 microg. In particular, patients who have used additional short-acting beta(2)-agonists as rescue medication during the days preceding the induction, are at high risk.

Exercise-induced bronchoconstriction depends on exercise load

Exercise-induced bronchoconstriction (EIB) is often used as a measure of bronchial hyperresponsiveness and employed in epidemiological studies. Different tests are used, including free running tests with poor standardization of exercise load. The present study aimed to assess the role of exercise load in relationship to level of EIB.

METHODS

20 asthmatic children, 9-17 years old with a history of EIB, underwent two treadmill test with 85% and 95% exercise load. The children ran with increasing speed for the first 2 min until reaching a heart rate of 85% or 95% of calculated maximum (220-age) and maintained this speed for the last 4 min. Lung function was measured before running, and 0, 3, 6, 10 and 15 min after the run. Borg scale for perceived exertion was employed for children's self-evaluation of exercise load.

RESULTS

Peak heart rate, mean Borg score during 85% exercise load was 178.7/13.6 and during 95% was 194.3/18.2 (P<0.001). Maximum fall in FEV1 after 85% exercise load was 8.84% vs. 25.11% after 95% (P<0.001). Nine subjects (40%) fell > or = 10% in FEV1 after 85% exercise load vs. 20 subjects (100%) after 95% exercise load. EIB from the 95% exercise load test had markedly higher correlation with serum ECP (r=0.77, P<0.001).

CONCLUSION

Exercise load is essential for the interpretation of EIB, and strict standardization of exercise tests should be undertaken. The EIB from the high exercise load tests seemed better correlated to inflammatory activity than the low exercise load test.

Effect of sputum induction on spirometric measurements and arterial oxygen saturation in asthmatic patients, smokers, and healthy subjects

BACKGROUND

Sputum production induced by inhalation of hypertonic saline solution has been proposed as a technique to collect secretions and inflammatory cells from the airways of subjects with bronchial asthma or with a history of smoking. The aim of this study was to determine the effect of a sputum induction procedure on spirometric results and arterial oxygen saturation (SaO(2)) in asthmatic patients, smokers, and healthy subjects.

METHODS

We recruited 14 subjects suffering from asthma (11 men and 3 women; age range, 18 to 49 years), 14 subjects with a history of smoking (5 men and 9 women; age range, 23 to 64 years), and 9 healthy volunteers (7 men and 2 women; age range, 28 to 54 years). To obtain a sample of induced sputum, all subjects inhaled a mist of 3% hypertonic saline solution nebulized for 5 min and repeated the cycle no more than four times. Asthmatic patients were pretreated with 200 microg salbutamol (inhaled). During sputum induction, the transcutaneous SaO(2) was continuously measured and baseline, fall, and the differences between baseline and fall SaO(2) were recorded. Additionally, we measured the duration of mild desaturation (change in SaO(2), < 4%) and of marked desaturation (change in SaO(2), > 5%) in each subject. Finally, baseline FEV(1) and changes in FEV(1) as a percentage of baseline values were recorded in all subjects.

RESULTS

We found that baseline and fall SaO(2) values for the three groups were similar. However, in each group a significant mean change in SaO(2) was evident during sputum production (asthmatic patients, 6.0%; smokers, 5.3%; healthy subjects, 6.0%). Moreover, the mean durations of mild desaturation were 7 min, 21 s in asthma patients; 8 min, 24 s in smokers; and 7 min, 16 s in healthy subjects. Similarly, the durations of marked desaturation were 1 min, 25 s in asthmatic patients, 1 min, 19 s in smokers, and 1 min, 21 s in healthy subjects. The mean (+/- SD) fall in FEV(1) was not statistically different among the three groups (asthmatic patients, 1.36 +/- 5.6%; smokers, 7.58 +/- 11.76%; and healthy subjects, 0.05 +/- 9.6%). However, one smoker did experience excessive bronchoconstriction (fall in FEV(1), > 20%).

CONCLUSIONS

This study demonstrated a significant and comparable fall in SaO(2) during sputum induction by inhalation of hypertonic saline solution in asthmatic patients, smokers, and healthy subjects. The results suggest that subjects who are hypoxemic before sputum induction require SaO(2) monitoring during the procedure.

Serum eosinophil cationic protein and bronchial responsiveness in pediatric and adolescent asthma patients

BACKGROUND

Serum eosinophil cationic protein (ECP) has been promoted as a marker of inflammatory activity in bronchial asthma. Bronchial responsiveness, measured either by inhaling pharmacologically active substances such as histamine or methacholine, or by applying physical stimuli such as the hyperventilation of cold dry air, is also considered to be an indirect marker of bronchial inflammation.

OBJECTIVES

In this study, we investigated the possible relationship between serum ECP and bronchial responsiveness to both cold dry air and histamine in presently symptom- and medication-free pediatric and adolescent asthma patients.

SUBJECTS

Thirty-six children and adolescents with atopic asthma were studied.

METHODS

On 2 consecutive days, bronchial responsiveness was assessed nonpharmacologically by cold dry air and pharmacologically by histamine in random order. Blood samples for determination of ECP were collected before each challenge.

RESULTS

Serum ECP levels correlated with neither cold dry air-induced changes in FEV1 nor the provocation concentrations of histamine causing a 20% fall in FEV1. Subjects with bronchial hyperresponsiveness to cold dry air and histamine had somewhat higher levels of serum ECP than subjects with normal responses, but these differences were insignificant.

CONCLUSIONS

Our results indicate a lack of relationship both between serum ECP and bronchial responsiveness to cold dry air and between serum ECP and bronchial responsiveness to histamine.

Smoking and airway hyperresponsiveness especially in the presence of blood eosinophilia increase the risk to develop respiratory symptoms: a 25-year follow-up study in the general adult population

Airway hyperresponsiveness (AHR) constitutes a risk for development of respiratory symptoms. We assessed whether blood eosinophilia (>/= 275 eosinophils/microliters), skin test positivity (sum score >/= 3) and cigarette smoking (never, ex-smoker, 1-14 cig/d, 15-24 cig/d, >/= 25 cig/d) at the first of two successive surveys are related to the development of respiratory symptoms (chronic cough or phlegm, bronchitis, persistent wheeze, dyspnea, and asthma) at the second survey, and whether these relations are the same in subjects with (PC10 </= 8 mg/ml histamine) and without AHR. We analyzed data of the longitudinal Vlagtwedde-Vlaardingen Study (1965 to 1990) using logistic regression analyses with paired observations, taking multiple measurements within a person into account. In total, 995 men and 792 women contributed 4,403 paired observations. Eosinophilia in hyperresponsive subjects significantly increased the risk to develop one or more respiratory symptoms (odds ratio [OR] = 3.67, 95% confidence interval [CI] = 1.79 to 7.52), wheeze (OR = 5. 06, 95% CI = 2.11 to 12.13), and dyspnea (OR = 2.73, 95% CI = 1.13 to 6.60), independent of smoking, age, sex, area of residence, and time between two successive surveys. Smoking at the first of two successive surveys increased the risk to develop symptoms in a dose-dependent relation. Subjects with positive skin tests in the past were less likely to develop one or more respiratory symptoms (OR = 0.64, 95% CI = 0.46 to 0.88) and chronic phlegm (OR = 0.65, 95% CI = 0.42 to 1.00), independent of AHR. This longitudinal study in the general adult population shows that cigarette smoking and hyperresponsive subjects are at increased risk to develop respiratory symptoms, and especially so when eosinophilia is present in hyperresponsive persons.

Exhaled nitric oxide (NO) is reduced shortly after bronchoconstriction to direct and indirect stimuli in asthma

Exhaled NO is increased in patients with asthma and may reflect disease severity. We examined whether the level of exhaled NO is related to the degree of airway obstruction induced by direct and indirect stimuli in asthma. Therefore, we measured exhaled NO levels before and during recovery from histamine and hypertonic saline (HS) challenge (Protocol 1) or histamine, adenosine 5'-monophosphate (AMP), and isotonic saline (IS) challenge (Protocol 2) in 11 and in nine patients with mild to moderate asthma, respectively. The challenges were randomized with a 2-d interval. Exhaled NO and FEV1 were measured before and at 4, 10, 20, and 30 min after each challenge. NO was measured during a slow VC maneuver with a constant expiratory flow of (0.05 x FVC)/s against a resistance of 1 to 2 cm H2O. Baseline exhaled NO levels were not significantly different between study days in Protocol 1 (mean +/- SD: 4.8 +/- 1.8 ppb [histamine] versus 5.4 +/- 2.1 ppb [HS], p = 0.4) or in Protocol 2 (7.9 +/- 4.7 ppb [histamine], 8.3 +/- 5.2 ppb [AMP], and 7.2 +/- 3.7 ppb [IS], p = 0.7). A significant reduction in exhaled NO was observed directly after HS (mean +/- SEM: 39.2 +/- 3.9 %fall) and AMP challenge (32.3 +/- 7.3 %fall) (MANOVA, p < 0.001), respectively, whereas exhaled NO levels tended to decrease after histamine challenge. Isotonic saline challenge did not induce changes in exhaled NO (p = 0.7). There was a positive correlation between %fall in FEV1 and the %fall in exhaled NO after histamine, HS, and AMP challenge as indicated by the mean slope of the within-subject regression lines (p <= 0.04). We conclude that acute bronchoconstriction, as induced by direct and indirect stimuli, is associated with a reduction in exhaled NO levels in asthmatic subjects. This suggests that airway caliber should be taken into account when monitoring exhaled NO in asthma.

Safety of inducing sputum in patients with asthma of varying severity

Inducing sputum using hypertonic saline is a noninvasive method to investigate airway inflammation in people with asthma. However, hypertonic saline may also induce bronchoconstriction in some patients. The aim of the study was to examine whether the overall safety of using hypertonic saline to induce sputum in patients with mild to moderate asthma could be extended to patients with severe and/or uncontrolled asthma. Nine control subjects and 64 asthmatic patients with varying severity of the disease (FEV1 40-126% predicted values) were studied. Twenty-one of those patients had uncontrolled asthma. Sputum was induced in a standardized manner using hypertonic saline. The safety of the procedure was evaluated by assessing the clinical response and measuring FEV1 just before and during sputum induction. The procedure was well tolerated in most patients, but it had to be stopped due to side effects in 11.6% of patients with severe asthma. None of the side reactions were severe. Few patients with uncontrolled (17.3%) or severe asthma (18.6%) had a drop in FEV1 of 10-20%. The fall in FEV1 was significantly greater in patients with severe asthma than those with mild disease (p < 0.02 Mann-Whitney U test). We conclude that hypertonic saline-induced sputum is a safe technique even in patients with severe asthma.