Increased parasympathetic tone as the underlying cause of asthma: a hypothesis

Neonatal rhinorrhea, heart rate variability, and childhood exercise-induced wheeze

Background

There is increasing evidence linking infant rhinorrhea to school-age exercise-induced wheeze (EIW) via a parasympathetic nervous system pathway. The ratio of the root mean square of successive differences in heart beats (RMSSD) measured in quiet sleep versus active sleep (RMSSDQS:AS) is a novel biomarker in asthma.

Objective

We tested the hypotheses that (1) neonatal rhinorrhea predicts childhood EIW independent of other neonatal respiratory symptoms, (2) neonatal RMSSDQS:AS predicts childhood EIW, and (3) RMSSDQS:AS mediates the association between neonatal rhinorrhea and childhood EIW.

Methods

Participants from the Safe Passage/Environmental Influences on Child Health Outcomes (PASS/ECHO) prospective birth cohort had heart rate variability extracted from electrocardiogram traces acquired in the first month of life. Parents reported on rhinorrhea in their child at age 1 month and on EIW in their child at ages 4 to 11 years.

Results

In models (N = 831) adjusted for potential confounders and covariates, including neonatal wheeze, cough and fever, neonatal rhinorrhea-predicted childhood EIW (relative risk [RR] = 2.22; P = .040), specifically, among females (RR = 3.38; P = .018) but not males (RR = 1.39; P = .61). Among participants contributing data in both active and quiet sleep (n = 231), RMSSDQS:AS predicted EIW (RR = 2.36; P = .003) and mediated the effect estimate of neonatal rhinorrhea predicting EIW among females. Half of the females with a higher RMSSDQS:AS and neonatal rhinorrhea (n = 5 of 10) developed EIW as compared with 1.8% of the other females (n = 2 of 109) (P < .001).

Conclusions

Our findings support dysregulation of the parasympathetic nervous system in infancy as one of the possible underlying mechanisms for the development of EIW later in childhood among females, which could aid in the development of future interventions.

The Role of Long-Acting Antimuscarinic Agents in the Treatment of Asthma

The journey of using anticholinergics in the treatment of asthma started with anticholinergic-containing plants such as Datura stramonium and Atropa belladonna, followed by ipratropium bromide and continued with tiotropium, glycopyrronium, and umeclidinium. Although antimuscarinics were used in the maintenance treatment of asthma over a century ago, after a long time (since 2014), it has been recommended to be used as an add-on long-acting antimuscarinic agent (LAMA) therapy in the maintenance treatment of asthma. The airway tone controlled by the vagus nerve is increased in asthma. Allergens, toxins, or viruses cause airway inflammation and inflammation-related epithelial damage, increased sensory nerve stimulation, ganglionic and postganglionic acetylcholine (ACh) release by inflammatory mediators, intensification of ACh signaling at M1 and M3 muscarinic ACh receptors (mAChRs), and dysfunction of M2 mAChR. Optimal anticholinergic drug for asthma should effectively block M3 and M1 receptors, but have minimal effect on M2 receptors. Tiotropium, umeclidinium, and glycopyrronium are anticholinergic agents with this feature. Tiotropium has been used in a separate inhaler as an add-on treatment to inhaled corticosteroid (ICS)/long-acting β2-agonist (LABA), and glycopyrronium and umeclidinium have been used in a single inhaler as a combination of ICS/LABA/LAMA in asthma in recent years. Guidelines recommend this regimen as an optimization step for patients with severe asthma before initiating any biologic or systemic corticosteroid therapy. In this review, the history of antimuscarinic agents, their effectiveness and safety in line with randomized controlled trials, and real-life studies in asthma treatment will be discussed according to the current data.

The new era of add-on asthma treatments: where do we stand?

Globally, a small proportion (5-12%) of asthma patients are estimated to have severe disease. However, severe asthma accounts for disproportionately high healthcare resource utilization. The Global Initiative for Asthma (GINA) management committee recommends treating patients with asthma with inhaled corticosteroids plus long-acting β2-agonists and, when needed, adding a long-acting muscarinic receptor antagonist or biologic agent. Five biologics, targeting different effectors in the type 2 inflammatory pathway, are approved for asthma treatment. However, biologics have not been compared against each other or add-on inhaled therapies in head-to-head clinical trials. As a result, their positioning versus that of current and anticipated small-molecule strategies is largely unknown. Furthermore, with the emergence of biomarkers for predicting response to biologics, a more personalized treatment approach-currently lacking with inhaled therapies-may be possible. To gain perspective, we reviewed recent advances in asthma pathophysiology, phenotypes, and biomarkers; the place of biologics in the management and personalized treatment of severe asthma; and the future of biologics and small-molecule drugs. We propose an algorithm for the stepwise treatment of severe asthma based on recommendations in the GINA strategy document that accounts for the broad range of phenotypes targeted by inhaled therapies and the specificity of biologics. In the future, both biologics and small molecules will continue to play key roles in the individualized treatment of severe asthma. However, as targeted therapies, their application will continue to be focused on patients with certain phenotypes who meet the specific criteria for use as identified in pivotal clinical trials.

Increased Heart Rate Variability Response Among Infants with Reported Rhinorrhea and Watery Eyes: A Pilot Study

Introduction

Previously, we found that reported infant rhinorrhea and watery eyes without a cold (RWWC) predicted school age exercise-induced wheeze, emergency department visits, and hospitalizations. These findings were independent of allergic sensitization, and we theorized that increased parasympathetic tone underlay the association. We also reported that increased heart-rate variability (HRV) in infants predicted wheeze in 2–3 year-olds. In a convenience sample of children participating in a birth cohort study, we tested the hypothesis that infants with RWWC would have elevated HRV, indicating increased parasympathetic tone.

Methods

RWWC symptoms since birth were queried for 3-month-old children. At 4-months, HRV was assessed (root mean square of successive differences [RMSSD]) during a standardized infant–mother still-face paradigm, which included 2 minutes of mother/child play immediately followed by 2 minutes of the mother maintaining a still-face.

Results

Among participants (n=38), RWWC was common for girls (32%) and boys (21%). The children with the greatest decrease in RMSSD between play and still-face challenge (lowest tertile) had a higher prevalence of RWWC as compared with children in the higher tertiles (50% vs 16%, P=0.045). In a logistic regression model controlling for sex, age and time between HRV and RWWC assessment, children with greater decrease in HRV between play and still-face (lowest tertile) had greater odds of having RWWC (odds ratio=6.0, P=0.029).

Conclusion

In this relatively small study, we demonstrated greater decreases in HRV in response to a stressor among children with reported RWWC, suggesting that these children might have increased parasympathetic tone and/or overall greater vagal reactivity.

Report of prenatal maternal demoralization and material hardship and infant rhinorrhea and watery eyes

BACKGROUND

Previously, we found that reported infant rhinorrhea and watery eyes without a cold (RWWC) predicted school age exercise-induced wheezing, emergency department visits, and respiratory-related hospitalizations for asthma. These findings appeared independent of infant wheezing and allergy. Overall, we theorize that prenatal material hardship and psychosocial distress can induce infant dysregulation in the autonomic nervous system leading to infant RWWC and school age exercise-induced wheezing.

OBJECTIVE

To test the hypotheses that indicators of prenatal stress and measures of maternal demoralization, which can alter infant autonomic nervous system responses, would predict infant RWWC.

METHODS

In a prospective birth cohort of urban children (n = 578), pregnant women were queried in the third trimester about material hardship and maternal demoralization using validated instruments. Child RWWC was queried every 3 months in infancy.

RESULTS

Notably, 44% of the mothers reported not being able to afford at least one of the basic needs of daily living during pregnancy, and children of those mothers were more likely to have infant RWWC (P < .001). The children had an increased risk of RWWC with increasing maternal demoralization during pregnancy (P < .001). In models controlling for sex, race and ethnicity, maternal asthma, maternal allergy, smoker in the home (pre- or postnatal), prenatal pesticide exposure, and older siblings, RWWC was predicted by mother's report of material hardship (relative risk, 1.22; P = .021) and maternal demoralization (relative risk, 1.14; P = .030).

CONCLUSION

These results suggest an association between material hardship and psychological distress during pregnancy and RWWC in infancy, further supporting a link between infant autonomic dysregulation and RWWC.

Cardiac autonomic modulation assessed by heart rate variability in children with asthma

OBJECTIVE

To assess cardiac autonomic modulation, measured by short-term frequency domain analysis of heart rate variability (HRV), in children with asthma.

METHODS

We conducted an observational study at a tertiary care teaching hospital. The sample consisted of 119 children aged 7 to 15 years with asthma and 56 age-matched healthy controls. Frequency domain HRV measures included low-frequency (LF; 0.04-0.15 Hz), high-frequency (HF; 0.15-0.4 Hz), and LF/HF ratio. The LF and HF components were expressed in both absolute values of power (ms² ) and in normalized units (nu).

RESULTS

Compared with healthy controls, asthmatic children had significantly higher value of HF (nu) (mean ± standard deviation: 45.9 ± 14.6 vs 40.7 ± 13.6; P = .02), and lower values of LF (nu) (54.1 ± 14.6 vs 59.3 ± 13.6; P = .02) and LF/HF ratio (median, interquartile range: 1.12, 0.82-1.88 vs 1.59, 1.02-2.08; P = .03). We did not find significant differences between children with persistent and intermittent asthma, and between children with well-controlled and partially-controlled or uncontrolled asthma, in terms of HRV measures.

CONCLUSIONS

Children with stable chronic asthma may have a cardiac autonomic imbalance with a possible enhanced parasympathetic modulation, as assessed by short-term frequency domain analysis of HRV. Neither asthma severity nor asthma control was significantly associated with HRV measures, but the study did not have enough power to draw a firm conclusion on this point.

New perspectives on the role of muscarinic antagonists in asthma therapy

INTRODUCTION

There is increasing evidence that tiotropium, a long-acting muscarinic agent (LAMA), is useful in the presence of severe-uncontrolled asthma despite the optimization of therapy with inhaled corticosteroids (ICSs) and long-acting β₂ agonists (LABAs) as recommended by the current guidelines. Furthermore, in recent years there have been several  preclinical and clinical studies on the pharmacological and therapeutic impact of other LAMAs in asthma.

AREAS COVERED

We have conducted an extensive search on muscarinic antagonists in asthma therapy throughout several sources and discuss what has emerged in the last 3 years (January 2017-March 2020).

EXPERT OPINION

New evidence indicates that the effectiveness of adding a LAMA, at least tiotropium, is independent of the degree of the type 2 inflammation and age of patient. Therefore, tiotropium can be administered without the need for patient phenotyping. Umeclidinium and glycopyrronium also appear effective in asthma. Initial treatment with LAMA+ICS for those with mild asthma may be an equally effective therapeutic option as LABA+ICS but this hypothesis should be confirmed by statistically powered trials.

Circadian rhythm of airways caliber and its autonomic modulation

The autonomic nervous system (ANS) is one of the effector pathways for circadian variation of many physiological parameters. Autonomic tone and airways caliber have been reported to exhibit circadian variation in separate studies. A simultaneous investigation of heart rate variability (HRV) and airway caliber might ascertain how airway caliber is modulated by autonomic tone. This study was planned to identify the variations in airway caliber and autonomic function tone during a 24-hour span. A total of 56 healthy male subjects with almost similar daily routines were studied. Time domain, frequency domain and nonlinear analysis of R-R interval from 5 min electrocardiogram (ECG) was done seven times during the daytime wake span at 3-hour intervals starting at 05:00 h in the morning until 23:00 h in the night. Simultaneously peak expiratory flow rate (PEFR) was determined using a mini Wright's peak flow meter. Rhythmometric analysis was done for PEFR and HRV parameters. Significant circadian variation in low frequency (LF) and high frequency (HF) variance was identified in this group of healthy subjects. The circadian rhythm of LF variance was characterized by a gradual increase and corresponding reciprocal change in HF variance from morning until night. The LF/HF ratio and SD2/SD1 ratio reflecting sympatho-vagal balance showed low to high values from morning to evening. The acrophase of the PEFR temporal pattern is similar to that of LF power and almost opposite in phase to that of HF power. PEFR is positively correlated with LF power. The circadian rhythm of airway caliber co-varies with cardiac autonomic tone. It appears that the temporal pattern of cardiac autonomic tone precedes in time that of airways caliber, thereby suggesting the latter operates under the modulatory effect of the 24-hour pattern in sympatho-vagal balance.

Sympathetic Nerve Hyperactivity in the Spleen: Causal for Nonpathogenic-Driven Chronic Immune-Mediated Inflammatory Diseases (IMIDs)?

Immune-Mediated Inflammatory Diseases (IMIDs) is a descriptive term coined for an eclectic group of diseases or conditions that share common inflammatory pathways, and for which there is no definitive etiology. IMIDs affect the elderly most severely, with many older individuals having two or more IMIDs. These diseases include, but are not limited to, type-1 diabetes, obesity, hypertension, chronic pulmonary disease, coronary heart disease, inflammatory bowel disease, and autoimmunity, such as rheumatoid arthritis (RA), Sjőgren's syndrome, systemic lupus erythematosus, psoriasis, psoriatic arthritis, and multiple sclerosis. These diseases are ostensibly unrelated mechanistically, but increase in frequency with age and share chronic systemic inflammation, implicating major roles for the spleen. Chronic systemic and regional inflammation underlies the disease manifestations of IMIDs. Regional inflammation and immune dysfunction promotes targeted end organ tissue damage, whereas systemic inflammation increases morbidity and mortality by affecting multiple organ systems. Chronic inflammation and skewed dysregulated cell-mediated immune responses drive many of these age-related medical disorders. IMIDs are commonly autoimmune-mediated or suspected to be autoimmune diseases. Another shared feature is dysregulation of the autonomic nervous system and hypothalamic pituitary adrenal (HPA) axis. Here, we focus on dysautonomia. In many IMIDs, dysautonomia manifests as an imbalance in activity/reactivity of the sympathetic and parasympathetic divisions of the autonomic nervous system (ANS). These major autonomic pathways are essential for allostasis of the immune system, and regulating inflammatory processes and innate and adaptive immunity. Pathology in ANS is a hallmark and causal feature of all IMIDs. Chronic systemic inflammation comorbid with stress pathway dysregulation implicate neural-immune cross-talk in the etiology and pathophysiology of IMIDs. Using a rodent model of inflammatory arthritis as an IMID model, we report disease-specific maladaptive changes in β₂-adrenergic receptor (AR) signaling from protein kinase A (PKA) to mitogen activated protein kinase (MAPK) pathways in the spleen. Beta₂-AR signal "shutdown" in the spleen and switching from PKA to G-coupled protein receptor kinase (GRK) pathways in lymph node cells drives inflammation and disease advancement. Based on these findings and the existing literature in other IMIDs, we present and discuss relevant literature that support the hypothesis that unresolvable immune stimulation from chronic inflammation leads to a maladaptive disease-inducing and perpetuating sympathetic response in an attempt to maintain allostasis. Since the role of sympathetic dysfunction in IMIDs is best studied in RA and rodent models of RA, this IMID is the primary one used to evaluate data relevant to our hypothesis. Here, we review the relevant literature and discuss sympathetic dysfunction as a significant contributor to the pathophysiology of IMIDs, and then discuss a novel target for treatment. Based on our findings in inflammatory arthritis and our understanding of common inflammatory process that are used by the immune system across all IMIDs, novel strategies to restore SNS homeostasis are expected to provide safe, cost-effective approaches to treat IMIDs, lower comorbidities, and increase longevity.

The evolving role of tiotropium in asthma

Tiotropium is a long-acting muscarinic antagonist (LAMA) that exerts its bronchodilatory effect by blocking endogenous acetylcholine receptors in the airways. Its safety and efficacy are well established for the treatment of COPD, and it is now being recognized for its role in improving lung function and control in asthma. This review discusses the evolving role of tiotropium delivered by the Respimat® in patients across the range of asthma severities and ages, and provides an overview of safety and efficacy data. Tiotropium is the only LAMA currently approved for the treatment of asthma, and evidence from a large-scale clinical trial program, including several Phase III studies in adults, has demonstrated that tiotropium improves lung function and asthma control, with a safety profile comparable with that of placebo. Clinical trials in adolescent patients (aged 12-17 years) have also shown improvements in lung function and trends toward improved asthma control. Of note, the efficacy and safety profiles are consistent regardless of baseline characteristics and phenotype. Given the large and growing body of evidence, it is likely that as clinical experience with tiotropium increases, this treatment may possibly emerge as the key choice for add-on therapy to inhaled corticosteroids/long-acting β2-agonists, and in patients who do not tolerate long-acting bronchodilators or other medications, in the future.

Umeclidinium for the treatment of uncontrolled asthma

INTRODUCTION

Smooth muscle cell contraction in the airways is the principal therapeutic target in asthmatic subjects and its insufficient treatment is often a cause of uncontrolled disease. For this reason, research has focused on targeting smooth muscle activity with anticholinergic agents, including umeclidinium. Areas covered: This review highlights the potential application of umeclidinium, a long acting muscarinic antagonist, as a novel therapeutic approach for patients with severe uncontrolled asthma, despite maximal therapy. Expert opinion: Umeclidinium, similarly to tiotropium, which has been recently included in guidelines, may act by contrasting cholinergic activation in airways, preventing or at least reducing smooth muscle cells contraction and the consequent bronchoconstriction. This is similar to what occurs in chronic obstructive pulmonary disease, for which umeclidinium has been regularly approved. However, available data is not sufficient and further studies are needed before regulatory approval can be sought, since only phase II clinical trials have been conducted at present. Both quality of life and objectifiable clinical data and parameters must be assessed, including lung function improvements, reduction of exacerbations and reduction of as required medications.

Role of muscarinic antagonists in asthma therapy

INTRODUCTION

Higher parasympathetic tone has been reported in asthmatics. In general, cholinergic contractile tone is increased by airway inflammation associated with asthma. Nevertheless, the role of muscarinic antagonists for the treatment of asthma has not yet been clearly defined. Areas covered: The use of SAMAs and LAMAs in asthma has been examined and discussed according with the published evidence. Particular attention has been given to the large Phase III clinical trial program designed to evaluate the efficacy and safety of tiotropium respimat added to standard treatment in adults, adolescents and children with persistent asthma across the spectrum of asthma severity. Expert commentary: The current evidence is that in patients with poorly controlled severe asthma despite the use of ICS and LABA, the addition of tiotropium significantly increases the time to the first severe exacerbation and provides a modest but sustained bronchodilation. Identical results should be produced using other LAMAs. In any case, the documentation that, at least in animal or in vitro models, LAMAs show significant anti-inflammatory and anti-proliferative capacities and are able to inhibit airway remodeling induced by allergens makes a strong presumption that the use of LAMAs in asthma may go beyond the simple bronchodilator effect.

Positioning of Long-Acting Muscarinic Antagonists in the Management of Asthma

Despite a range of efficacious therapies for asthma, including inhaled corticosteroids (ICS) and long-acting β₂-agonists (LABA), a significant proportion of patients have poor asthma control and retain a risk of future worsening of their symptoms. Long-acting muscarinic antagonist (LAMA) bronchodilators offer a well-tolerated, efficacious, and cost-effective add-on to a patient's treatment. Of the LAMAs currently under investigation or available for the treatment of asthma, evidence from a comprehensive clinical trial program in adults and children shows that once-daily treatment with tiotropium provides benefits for patients with uncontrolled asthma despite the use of ICS and LABAs. Tiotropium is included in the Global Initiative for Asthma (GINA) strategy document as an add-on therapy option for patients at Step 4 or 5 with a history of asthma exacerbations. Tiotropium Respimat® has demonstrated safety and efficacy in patients with a range of disease severities, ages, and phenotypes. This review describes the evidence for the use of LAMA as add-on therapy for patients with asthma who remain uncontrolled despite the use of ICS and LABA treatments.

Tiotropium for the treatment of asthma: a drug safety evaluation

INTRODUCTION

Tiotropium, a once-daily long-acting anticholinergic bronchodilator, has recently been approved for use in the treatment of asthma in a number of countries, including the EU and the USA, and was incorporated into the 2015 update of the Global Initiative for Asthma treatment guidelines. Here we review safety data from published clinical trials to help inform the use of tiotropium in the treatment of patients with asthma.

AREAS COVERED

Safety data from recently published clinical trials, which compared tiotropium with placebo or an active control, were reviewed. Trials included children, adolescents, and adults across severities of symptomatic asthma, and assessed tiotropium delivered via the Respimat and HandiHaler devices.

EXPERT OPINION

Based on the reviewed scientific evidence, tiotropium is a safe and well-tolerated long-acting anticholinergic bronchodilator for use in the treatment of asthma. In the trials assessed, the safety of tiotropium was found to be comparable with that of placebo and alternative therapeutic options, including a doubling in the dose of inhaled corticosteroids and the long-acting β2-agonist salmeterol.

Can bronchial asthma with an highly prevalent airway (and systemic) vagal tone be considered an independent asthma phenotype? Possible role of anticholinergics

Recently, we studied occurrence and role of non-respiratory symptoms (n-RSs) before a worsening of asthma symptoms. Some n-RSs such as anxiety, reflux, heartburn, abdominal pain, which appeared within 3 h before the onset of an asthma attack, are the likely result of an imbalance between sympathetic/parasympathetic systems with an increase in cholinergic tone. Therefore, it is likely that some of these n-RSs induced by the increased cholinergic tone might be present related with specific parasympathetic-associated respiratory symptoms such as those elicited by airway narrowing. It is likely that, at least in some categories of asthmatics, an increased cholinergic tone, rather than other well-known factors, might play a prevalent role in triggering bronchospasm. If this is the case, it is possible to speculate that the use of anticholinergic agents (mainly those with long-acting activity) in patients suffering from asthma should be more beneficial in individuals characterized by a higher degree of cholinergic tone that, consequently might be the ideal target for the use of long-acting anticholinergics and, possibly, represent a novel asthma phenotype. The presence of parasympathetic-associated n-RSs might help the physician to identify this type of patients, although this might be followed by a more detailed assessment.

Bronchodilator response following methacholine-induced bronchoconstriction predicts acute asthma exacerbations

Methacholine bronchial provocation test provides the concentration of methacholine causing a 20% decrease in forced expiratory volume in 1 s (FEV1) from baseline (PC20). The dose-response slope (DRS), and other continuous indices of responsiveness (CIR; the percentage decline from the post-diluent baseline FEV1 after the last dose of methacholine), and per cent recovery index (PRI; the percentage increase from the maximally reduced FEV1 after bronchodilator inhalation) are alternative measures. The clinical relevance of these indices in predicting acute asthma exacerbations has not been fully evaluated.In two prospective cohorts of childhood and elderly asthmatics, baseline PC20, DRS, CIR and PRI were measured and evaluated as predictors of acute asthma exacerbations.We found that PRI was significantly related to the presence of asthma exacerbations during the first year of follow-up in both cohorts of childhood (p=0.025) and elderly asthmatics (p=0.003). In addition, PRI showed a significant association with the total number of steroid bursts during 4.3 years of follow-up in the cohort of childhood asthmatics (p=0.04).We demonstrated that PRI, an index of reversibility following methacholine-induced bronchoconstriction, was a good clinical predictor of acute exacerbations of asthma in both childhood and elderly asthmatics.

Is there a rationale and role for long-acting anticholinergic bronchodilators in asthma?

Despite current guidelines and the range of available treatments, over a half of patients with asthma continue to suffer from poor symptomatic control and remain at risk of future worsening. Although a number of non-pharmacological measures are crucial for good clinical management of asthma, new therapeutic controller medications will have a role in the future management of the disease. Several long-acting anticholinergic bronchodilators are under investigation or are available for the treatment of respiratory diseases, including tiotropium bromide, aclidinium bromide, glycopyrronium bromide, glycopyrrolate and umeclidinium bromide, although none is yet licensed for the treatment of asthma. A recent Phase III investigation demonstrated that the once-daily long-acting anticholinergic bronchodilator tiotropium bromide improves lung function and reduces the risk of exacerbation in patients with symptomatic asthma, despite the use of inhaled corticosteroids (ICS) and long-acting β₂-agonists (LABAs). This has prompted the question of what the rationale is for long-acting anticholinergic bronchodilators in asthma. Bronchial smooth muscle contraction is the primary cause of reversible airway narrowing in asthma, and the baseline level of contraction is predominantly set by the level of ‘cholinergic tone’. Patients with asthma have increased bronchial smooth muscle tone and mucus hypersecretion, possibly as a result of elevated cholinergic activity, which anticholinergic compounds are known to reduce. Further, anticholinergic compounds may also have anti-inflammatory properties. Thus, evidence suggests that long-acting anticholinergic bronchodilators might offer benefits for the maintenance of asthma control, such as in patients failing to gain control on ICS and a LABA, or those with frequent exacerbations.

Autonomic nervous system dysfunction and their relationship with disease severity in children with atopic asthma

The involvement of autonomic imbalance has been reported in the pathogenesis of allergic diseases. The aim of this study was to investigate the association between the clinical severity of childhood asthma with autonomic nervous system (ANS) dysfunction and to define whether the severity of asthma correlates with ANS activity. In this case-control study, we evaluated the ANS activity by testing heart rate variability (HRV) and sympathetic skin response (SRR) in 77 asthmatic children, age 7-12 yrs, who had no co-morbidity and compared them with 40 gender- and age-matched control subjects. According to the severity of their asthma, study subjects were further divided into three groups: I (mild asthmatics), II (moderate asthmatics), and III (severe asthmatics). Inter-group ANS scale scores differed significantly (p<0.01) between Groups I and III and between Groups II and III. Combined use of HRV and SSR provides a higher degree of sensitivity for assessing disease severity in cases of pediatric asthma.