Reflex heart rate control in asthma. Evidence of parasympathetic overactivity

Parasympathetic nervous system: A key role in control and mood disorders in patients with asthma

BACKGROUND

Patients with severe asthma often have uncontrolled disease and experience mood disorders, particularly anxiety and depression. The autonomic nervous system (ANS) plays an important role in asthma, mainly through the parasympathetic ANS system (PANS), which favors bronchoconstriction and mental health status.

OBJECTIVE

To evaluate the role of the activation of the PANS in uncontrolled asthma and related mood disorders.

METHODS

This was a proof-of-concept cross-sectional study that analyzed demographic and clinical variables reflecting asthma severity and control, lung function, inflammation (from induced sputum), evaluation of quality of life, and the risk for anxiety and depression according to validated questionnaires. The PANS analysis was conducted based on heart rate variability: SD of the difference between consecutive normal-to-normal (NN) intervals (SDNN), root mean square of the successive differences (RMSSD), percentage of consecutive NN intervals (pNN50), total power (TP), and respiratory-related power (Pr).

RESULTS

A total of 30 patients with asthma were grouped according to asthma control and the risk for anxiety and depression; 10 patients with uncontrolled asthma compared with the patients with controlled asthma showed significant differences (P < .05) in SDNN (26.5 [8.2] vs 42.7 [29.7]), RMSSD (14.1 [6.5] vs 24 [20]), pNN50 (0.6 [1.5] vs 6.2 [11.8]), TP (0.0005 [0.00046] vs 0.0014 [0.00085]), and Pr (0.0003 [0.00025] vs 0.0007 [0.00060]) respectively. A total of 13 patients at risk for anxiety and depression compared with the patients without showed reduced values (P < .05) for SDNN (26.5 [7.9] vs 45.6 [31.3]), pNN50 (0.75 [1.4] to 7.12 [12.6]), TP (0.0005 [0.00048] to 0.0012 [0.0008]), and Pr (0.0003 [0.00027] to 0.0008 [0.00062]).

CONCLUSION

Our results suggest that PANS activity is depressed in patients with uncontrolled asthma and common mood disorders such as depression and anxiety, and the evaluation of heart rate variability may be a useful means for follow-up of asthma control and related mood disorders.

Heart rate variability in horses with and without severe equine asthma

BACKGROUND

Equine asthma in severe form (severe equine asthma [sEA]) shares remarkable similarities with human asthma. Human studies detected changes in the autonomic nervous system function in asthmatic patients based on heart rate variability (HRV) analysis.

STUDY DESIGN

Observational study.

OBJECTIVES

To investigate the relationship between sEA and HRV in horses.

METHODS

Twenty horses diagnosed with sEA and 20 asymptomatic (non-sEA) horses were investigated. SEA horses showed clinical signs. The RR intervals of the ECG were recorded for 1 h at rest between 9 AM and 11 AM using a heart rate (HR) monitor. HRV data were calculated using Kubios software. Parameters recorded for the sEA and non-sEA groups were compared using one-way MANOVA model. The significance level was set at α = 0.05.

RESULTS

SD2 (mean 99.6 ± SD 25.3 vs. 42.5 ± 17.1), SDNN (82.7 ± 20.7 vs. 41.3 ± 14.3), TINN (398.1 ± 104.9 vs. 209.3 ± 71.9), SD2/SD1 ratio (1.7 ± 0.2 vs. 1.1 ± 0.3), Total power (4740.2 ± 1977.9 vs. 1503.0 ± 1179.3), LF (2415.3 ± 1072.4 vs. 707.4 ± 649.9), SD1 (60.9 ± 15.9 vs. 39.2 ± 14.1), RMSSD (86.0 ± 22.6 vs. 55.3 ± 19.8) and HF (1575.8 ± 902.5 vs. 578.1 ± 491.1) were lower in sEA horses compared with the non-sEA horses (p < 0.01 for each variable). SD2, SDNN, TNN, the SD2/SD1 ratio and Total power showed the greatest discriminatory power in differentiating the sEA and non-sEA groups.

MAIN LIMITATIONS

Small sample size.

CONCLUSION

Our findings indicate that like humans, asthmatic horses show an overall reduction in autonomic control. A relative increase of the parasympathetic modulation of the heart was also observed. After further investigations, HRV measurement might be a non-invasive approach to monitor autonomic nervous system responses of sEA horses.

Heart rate recovery in adult individuals with asthma

Slow heart rate recovery (HRR) after exercise is a predictor of overall mortality in individuals with and without cardiovascular or respiratory disorders. No data on adults with asthma are available. The purpose of the study is to evaluate the prevalence of slow HRR in these individuals as compared with those with chronic obstructive pulmonary disease (COPD). We performed a retrospective analysis of baseline characteristics and physiological response to the six-minute walking distance test of stable individuals with asthma or COPD. Slow HRR was defined as HRpeak - HR at 1 minute after end exercise <12 bpm. Individuals with asthma walked significantly longer (median (IQR): 455 (385-512) vs 427 (345-485) meters; p=0.005) with a lower prevalence of slow HRR (30.3% vs 49.0%, respectively: p<0.001) than those with COPD. Individuals with asthma and slow HRR were older and walked less than those with normal HRR, without any difference in airway obstruction or in disease severity. Multivariate analysis showed that only the difference HRpeak - baseline HR (∆HR), was a predictor of slow HRR in both groups. More than 30% of adult individuals with asthma may show slow HRR. Only exercise ∆HR but no baseline characteristic seems to predict the occurrence of slow HRR.

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.

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.

Noninvasive Cardiorespiratory Signals Analysis for Asthma Evolution Monitoring in Preschool Children

OBJECTIVE

Despite its increasing prevalence, diagnosis of asthma in children remains problematic due to their difficulties in producing repeatable spirometric maneuvers. Moreover, low adherence to inhaled corticosteroids (ICS) treatment could result in permanent airway remodeling. The growing interest in a noninvasive and objective way for monitoring asthma, together with the apparent role of autonomic nervous system (ANS) in its pathogenesis, have attracted interest towards heart rate variability (HRV) and cardiorespiratory coupling (CRC) analyses.

METHODS

HRV and CRC were analyzed in 68 children who were prescribed ICS treatment due to recurrent obstructive bronchitis. They underwent three different electrocardiogram and respiratory signals recordings, during and after treatment period. After treatment completion, they were followed up during 6 months and classified attending to their current asthma status.

RESULTS

Vagal activity, as measured from HRV, and CRC, were reduced after treatment in those children at lower risk of asthma, whereas it kept unchanged in those with a worse prognosis.

CONCLUSION

Results suggest that HRV analysis could be useful for the continuous monitoring of ANS anomalies present in asthma, thus contributing to evaluate the evolution of the disease, which is especially challenging in young children.

SIGNIFICANCE

Noninvasive ANS assessment using HRV analysis could be useful in the continuous monitoring of asthma in children.

Nocturnal Heart Rate Variability Spectrum Characterization in Preschool Children With Asthmatic Symptoms

Asthma is a chronic lung disease that usually develops during childhood. Despite that symptoms can almost be controlled with medication, early diagnosis is desirable in order to reduce permanent airway obstruction risk. It has been suggested that abnormal parasympathetic nervous system (PSNS) activity might be closely related with the pathogenesis of asthma, and that this PSNS activity could be reflected in cardiac vagal control. In this work, an index to characterize the spectral distribution of the high frequency (HF) component of heart rate variability (HRV), named peakness ($\wp$), is proposed. Three different implementations of $\wp$, based on electrocardiogram (ECG) recordings, impedance pneumography (IP) recordings and a combination of both, were employed in the characterization of a group of preschool children classified attending to their risk of developing asthma. Peakier components were observed in the HF band of those children classified as high-risk ( $p < 0.005$), who also presented reduced sympathvoagal balance. Results suggest that high-risk of developing asthma might be related with a lack of adaptability of PSNS.

Airways disorders and the swimming pool

Concerns have been expressed about the possible detrimental effects of chlorine derivatives in indoor swimming pool environments. Indeed, a controversy has arisen regarding the possibility that chlorine commonly used worldwide as a disinfectant favors the development of asthma and allergic diseases. The effects of swimming in indoor chlorinated pools on the airways in recreational and elite swimmers are presented. Recent studies on the influence of swimming on airway inflammation and remodeling in competitive swimmers, and the phenotypic characteristics of asthma in this population are reviewed. Preventative measures that could potentially reduce the untoward effects of pool environment on airways of swimmers are discussed.

Autonomic dysfunction and clinical severity of disease in children with allergic rhinitis

OBJECTIVES

The involvement of autonomic imbalance has been reported in the pathogenesis of allergic diseases.

PURPOSE

To investigate the association between the clinical severity of childhood allergic rhinitis and autonomic nervous system (ANS) dysfunction, to define whether the severity of disease correlates with ANS activity.

METHODS

In this cross-sectional, case-control study, we evaluated the ANS testing by measuring sympathetic skin response (SRR) and heart rate (R-R) interval variation (RRIV) in 55 children with perennial allergic rhinitis (PAR), aged 7-12 yrs without any chronic co-morbidity, and the results were compared with 40 sex- and age-matched control subjects. The patients were divided into two groups according to the severity of allergic rhinitis.

RESULTS

There were significant increase in calculated RRIV variables during at rest and deep breathing in children with PAR compared to controls, which reflect parasympathetic nervous system (PNS) activity (p<0.005). The mean amplitude of SSR in patients, which reflect sympathetic nervous system (SNS) activity was smaller compared with the controls, but this difference was not significant (0.61±0.35 μV vs controls 0.94±0.46, p>0.05). Lower RRIV and the prolonged SSR latencies in children with AR were closely correlated with disease severity (r=-0.65, p<0.05, and r=-0.59, p<0.05 respectively).

CONCLUSION

Combined use of these two tests, allows separate testing of PNS and SNS function, and are very sensitive methods in assessing of severity of disease in children with PAR.

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.

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

Asthma is a chronic inflammatory disease of airways that is characterized by increased responsiveness of the tracheo-bronchial tree to multiple number of stimuli. Immunological theory does not explain all features in asthma, for example hyper-reactivity of the airways. Neurogenic theory also fails to explain the pathogenesis of asthma comprehensively. Higher parasympathetic tone has been reported in asthmatics but has never been suggested as a major underlying cause of asthma. This article attempts to explain the occurrence of hyper-responsiveness, inflammatory/allergic reactions and broncho-constriction in asthma on a common basis of inherent higher parasympathetic tone in asthmatics. The higher background parasympathetic firing leads to increased nitric oxide (NO) production owing to its co-localization with acetylcholine (ACh) in inhibitory non-adrenergic and non-cholinergic (i-NANC) nerves. NO is a neurotransmitter of i-NANC system and it mediates bronchodilation. Increased NO release has been found to be responsible for hyper-responsiveness and increased inflammation in the airways. The authors suggest that an inherently higher background parasympathetic tone in concert with inflammation or a specific genetic background could modify the effects of NO on lung homeostasis in humans leading to increased susceptibility to an asthmatic state.

Psychological factors in asthma

Asthma has long been considered a condition in which psychological factors have a role. As in many illnesses, psychological variables may affect outcome in asthma via their effects on treatment adherence and symptom reporting. Emerging evidence suggests that the relation between asthma and psychological factors may be more complex than that, however. Central cognitive processes may influence not only the interpretation of asthma symptoms but also the manifestation of measurable changes in immune and physiologic markers of asthma. Furthermore, asthma and major depressive disorder share several risk factors and have similar patterns of dysregulation in key biologic systems, including the neuroendocrine stress response, cytokines, and neuropeptides. Despite the evidence that depression is common in people with asthma and exerts a negative impact on outcome, few treatment studies have examined whether improving symptoms of depression do, in fact, result in better control of asthma symptoms or improved quality of life in patients with asthma.

Chronic stress, salivary cortisol, and alpha-amylase in children with asthma and healthy children

The present study examined whether chronic stress is related to daily life levels of salivary alpha-amylase (sAA), a marker for sympathetic activity, and cortisol in healthy children versus children with asthma. Children's sAA and cortisol levels were measured repeatedly over 2 days. Chronic stress measures included interviews with children about chronic home life stress and interviews with parents about one marker of socioeconomic status, parental education. Among children with asthma, higher chronic stress was associated with lower daily sAA output, while among healthy children, higher chronic stress was associated with flatter cortisol slopes. In conclusion, chronically stressed children with asthma showed lower salivary alpha-amylase output, indicating lower sympathetic activity, and implying a possible mechanism for increased susceptibility to symptom exacerbations. In contrast, higher cortisol levels in healthy children with chronic stress may indicate, for example, an increased risk for infectious diseases. This dichotomy emphasizes the different biological effects of chronic stress depending on illness status.

Autonomic nervous system control of the cardiovascular and respiratory systems in asthma

Patients with asthma have exaggerated bronchoconstriction of their airways in response to certain indirect (e.g. cold air, allergens, dust, exercise) or direct (e.g. inhaled methacholine) stimuli. This 'hyper-reactivity' usually co-exists with airway inflammation, although the pathophysiological mechanisms underlying these changes are not fully understood. It is likely that this hyper-reactivity is associated with abnormal autonomic nervous system (ANS) control. In particular, the parasympathetic (vagal) component of the ANS appears to be implicated in the pathogenesis of asthma. In addition, several studies have suggested the existence of differential alteration in ANS function following exercise in asthmatics compared with non-asthmatic individuals. Several early studies suggested that the altered autonomic control of airway calibre in asthma might be reflected by a parallel change in heart rate. Cardiac vagal reactivity does indeed appear to be increased in asthma, as demonstrated by the cardiac response to various autonomic functions tests. However, other studies have reported a lack of association between bronchial and cardiac vagal tone, and this is in accord with the concept of system-independent ANS control. This review provides a discussion of cardiovascular-autonomic changes associated with either the pathophysiology of asthma per se or with asthma pharmacotherapy treatment. Previous investigations are summarised suggesting an apparent association between altered autonomic-cardiovascular control and bronchial asthma. The full extent of autonomic dysfunction, and its clinical implications, has yet to be fully determined and should be the subject of future investigation.

Hypoxemia and autonomic nervous dysfunction in patients with chronic obstructive pulmonary disease

OBJECTIVE

Hypoxemia is known to be associated with abnormal heart rate variability (HRV) that can reflect the severity of the illness and may have prognostic value in patients with chronic obstructive pulmonary disease (COPD). The aim of this study was to examine the relationship between the derangements in cardiac autonomic nervous function and the oxygenation status or degree of airflow obstruction in COPD patients by using HRV analysis.

METHODS

Thirty clinically stable COPD patients and 18 age-matched normal subjects were included in this study. The normalized high-frequency power (nHFP) and the low-/high-frequency power ratio (LFP/HFP) were used as indices of vagal activity and sympathovagal balance, respectively.

RESULTS

Although global HRV measures were all significantly decreased, the nHFP and LFP/HFP of COPD patients were not significantly different from those of normal controls. There was a negative correlation between nHFP and arterial partial pressure of O2 (PaO2) and a positive correlation between LFP/HFP and PaO2 in COPD patients. No correlation existed between forced expiratory volume in 1.0 s/forced vital capacity (FEV1/FVC), % predicted of FEV1 (%FEV1) and nHFP or LFP/HFP in COPD patients.

CONCLUSIONS

The resting autonomic nervous function of COPD patients is not different from that of normal controls. Though the degree of airway narrowing is not related to the cardiac autonomic nervous function, chronic hypoxemia can lead to enhanced cardiac vagal activity and depressed sympathetic activity in COPD patients. A worse oxygenation status is associated with increased cardiac vagal and decreased cardiac sympathetic activities in COPD patients.

Airflow and autonomic responses to stress and relaxation in asthma: the impact of stressor type

The impact of stress on respiratory airflow in asthmatics is unclear. Part of the uncertainty may spring from the different physiological effects of different stressors. Given their potential to elicit increases in parasympathetic vagal activity, stressful situations that present few opportunities for coping (passive coping stressors) may be particularly problematic for people with asthma. Thirty-one adult asthmatics participated in a protocol including a widely used passive coping stressor (the cold pressor test), an active coping stressor (mental arithmetic), an interview about an upsetting asthma-related incident (viewed as a potential passive coping stressor given the exposure to unpleasant memories), and progressive muscle relaxation. Repeated measurements of airflow (via peak expiratory flow), vagal tone (via heart rate variability), and other variables were obtained. The cold pressor test, asthma interview and progressive muscle relaxation produced significant decreases in airflow compared to the baseline period. The cold pressor test and progressive muscle relaxation produced significant, complementary increases in vagal tone. These results suggest that passive coping stressors and other stimuli (e.g., certain forms of relaxation) that elicit increased vagal tone may be associated with poorer asthma control, a view consistent with a significant negative correlation between the participant's mean vagal tone response to the tasks and score on a measure of asthma self-efficacy.

Physiology of long pranayamic breathing: Neural respiratory elements may provide a mechanism that explains how slow deep breathing shifts the autonomic nervous system

Pranayamic breathing, defined as a manipulation of breath movement, has been shown to contribute to a physiologic response characterized by the presence of decreased oxygen consumption, decreased heart rate, and decreased blood pressure, as well as increased theta wave amplitude in EEG recordings, increased parasympathetic activity accompanied by the experience of alertness and reinvigoration. The mechanism of how pranayamic breathing interacts with the nervous system affecting metabolism and autonomic functions remains to be clearly understood. It is our hypothesis that voluntary slow deep breathing functionally resets the autonomic nervous system through stretch-induced inhibitory signals and hyperpolarization currents propagated through both neural and non-neural tissue which synchronizes neural elements in the heart, lungs, limbic system and cortex. During inspiration, stretching of lung tissue produces inhibitory signals by action of slowly adapting stretch receptors (SARs) and hyperpolarization current by action of fibroblasts. Both inhibitory impulses and hyperpolarization current are known to synchronize neural elements leading to the modulation of the nervous system and decreased metabolic activity indicative of the parasympathetic state. In this paper we propose pranayama's physiologic mechanism through a cellular and systems level perspective, involving both neural and non-neural elements. This theoretical description describes a common physiological mechanism underlying pranayama and elucidate the role of the respiratory and cardiovascular system on modulating the autonomic nervous system. Along with facilitating the design of clinical breathing techniques for the treatment of autonomic nervous system and other disorders, this model will also validate pranayama as a topic requiring more research.

Effects of two nebulization regimens on heart rate variability during acute asthma exacerbations in children

Analysis of heart rate variability (HRV) has been used to evaluate changes in sympathovagal balance. The present study was designed to investigate the influence of two therapeutic regimens on autonomic cardiovascular regulation during acute asthma exacerbations (AAE). Twenty children, 7-13 years of age, with moderate or severe AAE were randomized in two equal groups to receive either 0.15 mg/kg/dose salbutamol (group 1) or a combination of lower-dose salbutamol (0.10 mg/kg/dose) and ipratropium bromide (5 mcg/kg/dose) (group 2). Exacerbations were treated with three nebulizations (Tx) of either regimen given 20 minutes apart. HRV indices [total power, high-frequency component (HF), low-frequency component (LF), and LF:HF ratio] were analyzed at specific time intervals during the management of AAE. Therapy had a significant time-dependent main effect on total power (p = 0.001), LF (p < 0.0001), and HF (p = 0.005) but reached only borderline significance for LF:HF ratio (p = 0.053). The decrease in LF was more pronounced in group 2 vs. group 1 at 10 minutes post-Tx1 (p = 0.034) and at 10 minutes post-Tx2 (p = 0.05), but there was no significant difference between groups at 10 and 20 minutes post-Tx3. There were no significant differences between groups in any of the other HRV indices. Both regimens improved FEV1 (p = 0.0001) to the same magnitude. During AAE, three consecutive inhalation treatments with either high-dose salbutamol-only or lower-dose salbutamol plus ipratropium bromide combination, resulting in similar FEV1 improvement, cause domination of sympathetic over parasympathetic nervous system of similar overall magnitude but distinct patterns of HRV indices.

Parasympathetic airway response and heart rate variability before and at the end of methacholine challenge

BACKGROUND

The autonomic nervous system plays a primary role in regulating airway caliber, and its dysfunction is likely to contribute to the pathogenesis of airways diseases. Moreover, some findings support the hypothesis that autonomic dysfunction and/or dysregulation contributes to the pathogenesis of airway hyperresponsiveness (AHR). Heart rate variability (HRV) spectral analysis allows identifying noninvasively perturbations of the autonomic system.

PURPOSES

We tested the relationship between AHR and cardiac parasympathetic tone assessed by HRV spectral analysis in patients submitted to a diagnostic methacholine bronchial challenge (MBC).

METHODS

Fifteen women and 38 men (age range, 18 to 56 years) participated in the study. The principal indications for MBC were suspected asthma, chronic cough, unexplained exercise-induced dyspnea, or cough. The R-R intervals were continuously recorded during the MBC. Autoregressive method was performed on two series of 256 R-R intervals extracted before and after the MBC to obtain low-frequency (LF) and high-frequency (HF) components.

RESULTS

The MBC distinguished 29 subjects without airway responsiveness (R-) and 24 responder or hyperresponsive subjects (R+): mean provocative dose of methacholine causing a 20% reduction in mean (+/- SD) FEV1 of 467 +/- 351 microg (range, 70 to 1,426 microg). The HF component expressed in normalized units (n.u.) [the index of parasympathetic modulation] was significantly higher in R+ than in R- at baseline, before MBC (21 +/- 21 n.u. vs 11 +/- 9 n.u., p < 0.05). Interestingly, R+ showed a significant increase of HF component after MBC (243 +/- 30 to 567 +/- 620 ms2 and 21 +/- 21 to 34 +/- 30 n.u., p < 0.01). For all subjects, HF (n.u.) calculated at baseline and after MBC were significantly influenced by the bronchial responsiveness (r2 = -0.28 and -0.51, respectively; p < 0.001).

CONCLUSION

In summary, we found that R+ had a significantly higher parasympathetic tone than R- at baseline, and that R+ showed a significant increase in cardiac reactivity after bronchial challenge. These findings demonstrate that the autonomic nervous system, which contributes to the pathogenesis of AHR, is closely linked to cardiac modulation.

Review article: supra-oesophageal manifestations of gastro-oesophageal reflux disease and the role of night-time gastro-oesophageal reflux

Gastro-oesophageal reflux disease (GERD) has been associated with a variety of supra-oesophageal symptoms, including asthma, laryngitis, hoarseness, chronic cough, frequent throat clearing and globus pharyngeus. GERD may be overlooked as the underlying mechanism for these symptoms because typical GERD symptoms may be absent, despite abnormal oesophageal acid exposure. Two basic mechanisms linking GERD with laryngeal symptoms have been proposed: direct contact of gastric acid with the upper airway, in some cases due to micro-aspiration, and a vagovagal reflex triggered by acidification of the distal portion of the oesophagus. Gastro-oesophageal reflux (GER) during sleep is believed to be an important mechanism for the development of supra-oesophageal complications of GERD, such as asthma and idiopathic pulmonary fibrosis (IPF). Several physiological changes during sleep, including prolonged oesophageal acid contact time, decreased upper oesophageal sphincter pressure, increased gastric acid secretion, decreased salivation, decreased swallowing and a decrease in conscious perception of acid, render an individual more susceptible to reflux-induced injury. Supra-oesophageal symptoms often improve in response to aggressive acid-suppressive therapy. However, many unanswered questions remain regarding the appropriate approach to diagnosis and treatment of patients with GERD-related supra-oesophageal symptoms. In this article we review the relationship between supra-oesophageal symptoms and GERD and, where possible, highlight the evidence supporting the role of night-time reflux as a contributing factor to these symptoms.

The Daily Pattern of Heart Rate, Body Temperature, Locomotor Activity, and Autonomic Nervous Activity in Congenitally Bronchial-Hypersensitive (BHS) and Bronchial-Hyposensitive (BHR) Guinea Pigs

We studied the characteristics of the rhythmicity of heart rate (HR), body temperature (BT), locomotor activity (LA) and autonomic nervous activity in bronchial-hypersensitive (BHS) and bronchial-hyposensitive (BHR) guinea pigs. For this purpose, HR, BT, LA, and electrocardiogram (ECG) were recorded from conscious and unrestrained guinea pigs using a telemetry system. Autonomic nervous activity was analyzed by power spectral analysis of heart rate variability. Nocturnal patterns, in which the values in the dark phase (20:00-06:00) were higher than those in the light phase (06:00-20:00), were observed in HR, BT and LA in both strains of guinea pigs. The autonomic nervous activity in BHS guinea pigs showed a daily pattern, although BHR guinea pigs did not show such a rhythmicity. The high frequency (HF) power in BHS guinea pigs was higher than that in BHR guinea pigs throughout the day. Moreover, the low frequency/high frequency (LF/HF) ratio in BHS guinea pigs was lower than that in BHR guinea pigs throughout the day. These results suggest that parasympathetic nervous activity may be predominant in BHS guinea pigs.

High-frequency modulation of heart rate variability during exercise in patients with COPD

STUDY OBJECTIVES

To evaluate cardiac autonomic modulation in patients with COPD during peak exercise.

METHODS

Fifty-three patients with COPD (mean FEV(1), 35% predicted [SD, 11% predicted]; mean PaO(2), 68 mm Hg [SD, 11 mm Hg]; mean PaCO(2), 40 mm Hg [SD, 7 mm Hg]; mean age, 61 years [SD, 10 years]; 26 women and 27 men) and 14 healthy control subjects aged 60 years (SD, 8 years) [seven women and seven men] were studied at rest and during ramped bicycle ergometry to their volitional peak. Patients were not receiving autonomic medications other than inhaled beta-agonist agents and/or anticholinergic agents. Control subjects were not receiving any medications. Cardiac autonomic modulation was assessed via time-frequency analysis (Wigner-Ville) of ECG-derived heart rate variability as the power in the low-frequency (LF) band (ie, 0.04 to 0.15 Hz) and the high-frequency (HF) band (ie, > 0.15 to 0.4 Hz) averaged from > 3 min at rest and minutes 2 through 5 of their exercise period.

RESULTS

Patients with COPD had a significantly increased mean, ln-transformed HF band from rest to peak exercise (9.9 ms(2) [SD, 1.4 ms(2)] vs 10.7 ms(2) [SD, 1.4 ms(2)], respectively; p < 0.01), while the HF band was unchanged for the control group (10.7 ms(2) [SD, 1.5 ms(2)] vs 10.4 ms(2) [1.3 ms(2)], respectively; difference not significant). The mean ln-transformed LF band was significantly increased from rest to peak exercise in patients with COPD (10.9 ms(2) [SD, 1.5 ms(2)] vs 11.5 ms(2) [SD, 1.4 ms(2)], respectively; p < 0.01) and in control subjects (10.9 ms(2) [SD, 1.5 ms(2)] vs 11.5 ms(2) [SD, 1.3 ms(2)], respectively; p < 0.01). The mean LF/HF ratio was significantly decreased from rest to peak exercise in patients with COPD (3.1 [SD, 1.5] vs 2.5 [SD, 1.0], respectively; p < 0.01) and was increased in control subjects (1.9 [SD, 0.8] vs 2.4 [1.0], respectively; p < 0.01). When expressed in normalized units ([absolute power of the components]/[total power - very low frequency power] x 100), the HF band was again significantly greater during peak exercise than at rest in the patients with COPD and was unchanged during peak exercise for the control group. Autonomic changes were not significantly correlated with age, gender, body mass index, spirometry, lung volumes, resting gas exchange, or oxygen saturation during exercise.

CONCLUSION

These data suggest that, in contrast to control subjects, the balance of sympathetic to parasympathetic cardiac modulation decreases in patients with COPD during maximal volitional exercise.

Psychological aspects of asthma

Asthma can be affected by stress, anxiety, sadness, and suggestion, as well as by environmental irritants or allergens, exercise, and infection. It also is associated with an elevated prevalence of anxiety and depressive disorders. Asthma and these psychological states and traits may mutually potentiate each other through direct psychophysiological mediation, nonadherence to medical regimen, exposure to asthma triggers, and inaccuracy of asthma symptom perception. Defensiveness is associated with inaccurate perception of airway resistance and stress-related bronchoconstriction. Asthma education programs that teach about the nature of the disease, medications, and trigger avoidance tend to reduce asthma morbidity. Other promising psychological interventions as adjuncts to medical treatment include training in symptom perception, stress management, hypnosis, yoga, and several biofeedback procedures.

Prevalence and mechanisms of development of asthma and airway hyperresponsiveness in athletes

A high prevalence of asthma and airway hyperresponsiveness (AHR) has been reported in the athlete population. Factors potentially predisposing athletes to these conditions have not been clearly identified. Although moderate exercise has been shown to be beneficial in patients with asthma, repeated high-intensity exercise could possibly contribute to the development of asthma and AHR. This report provides an overview of the prevalence and possible mechanisms of development of asthma and AHR in the athlete population. The prevalence of asthma and AHR are higher in athletes than in the general population, particularly in swimmers and athletes performing sports in cold air environments. Possible mechanisms involved in the development of asthma in athletes are still uncertain; however, the content and physical characteristics of the inhaled air seem to be important factors, while immune and neurohumoral influences could play a modulatory role. This report stresses the need for further studies to better define the aetiologic factors and mechanisms involved in the development of asthma and AHR in athletes, and proposes relevant preventive and therapeutic measures.

Defensiveness and individual response stereotypy in asthma

OBJECTIVE

Previous literature has shown that the psychological trait of defensiveness is related to elevated sympathetic reactivity to stress and to several cardiac risk factors. The aim of this study was to examine whether these previous findings on defensiveness extend to an asthmatic population.

METHODS

Defensiveness was measured by the Marlowe-Crowne Social Desirability Scale using a quartile split: high (upper 25%) and low (bottom 75%). Twenty-two defensive and 66 nondefensive participants with asthma were exposed to laboratory tasks (initial baseline rest period, reaction time task, and a shop accident film).

RESULTS

During the tasks there was evidence of lower skin conductance levels and greater respiratory sinus arrhythmia amplitudes among defensive patients with asthma. After exposure to the tasks, defensive patients with asthma showed a decline on spirometry test measures compared with nondefensive asthmatic patients, who displayed an increase.

CONCLUSIONS

These data confirm individual response stereotypy and suggest that defensiveness may be characterized by sympathetic hypoarousal and parasympathetic hyperarousal among patients with asthma. Future studies are needed to determine whether defensiveness is a risk factor for stress-induced bronchoconstriction.

Gastroesophageal reflux, asthma, and mechanisms of interaction

Gastroesophageal reflux (GER) is a potential trigger of asthma. The esophagus and lung interact through a variety of mechanisms. Esophageal acid-induced bronchoconstriction can be provoked by a vagally mediated reflex, whereby acid in the distal esophagus produces airway responses; by neural enhancement of bronchial reactivity, whereby esophageal acid augments airway hyperresponsiveness; or by microaspiration, in which small amounts of esophageal acid in the upper airway cause significant airway responses. Interestingly, even in the microaspiration model, the vagus nerve plays a significant role. Neurogenic inflammation in the lung may occur with either vagally mediated mechanisms or with microaspiration. The prevalence of reflux symptoms, esophagitis, and abnormal esophageal acid contact time is higher in patients with asthma than in control populations. Potential mechanisms, whereby asthma may predispose to the development of GER, include autonomic dysregulation, an increased pressure gradient differential between the thorax and the abdomen, a high prevalence of hiatal hernia, alterations in crural diaphragm function, and bronchodilator medication use. Further research will help define how the esophagus and lung interact.

Airway hyperresponsiveness in elite athletes

It has been suggested that high-level training could contribute to the development of airway hyperresponsiveness (AHR), but the comparative effects of different sports on airway function remains to be determined. We evaluated 150 nonsmoking volunteers 18 to 55 yr of age; 100 athletes divided into four subgroups of 25 subjects each according to the predominant estimated hydrocaloric characteristic of ambient air inhaled during training: dry air (DA), cold air (CA), humid air (HA) and a mixture of dry and humid air (MA), and 50 sedentary subjects. Each subject had a respiratory questionnaire, a methacholine challenge, allergy skin-prick tests, and heart rate variability recording for evaluation of parasympathetic tone. The athletes had a 49% prevalence of AHR (PC(20) < 16 mg/ml), with a mean PC(20) of 16.9 mg/ml, compared with 28% (PC(20): 35.4) in sedentary subjects (p = 0.009). The prevalence (%) of AHR and mean PC(20) (mg/ml) varied as followed in the four subgroups of athletes: DA: 32% and 30.9; CA: 52% and 15.8; HA: 76% and 7.3; and MA: 32% and 21.5 (p = 0.002). The estimated parasympathetic tone was higher in athletes (p < 0.001), but this parameter showed only a weak correlation with PC(20) (r = -0.17, p = 0.04). This study has shown a significantly higher prevalence of AHR in athletes than in the control group because of the higher prevalence in the CA and HA groups. Parasympathetic activity may act as modulator of airway responsiveness, but the increased prevalence of AHR in our athlete population may be related to the type and possibly the content of inhaled air during training.

Defecation-induced bronchospasm

Acute asthma exacerbations are common. Patients with asthma experience symptoms in response to a wide variety of stimuli, and identifying the precipitating cause may be useful in guiding treatment and preventing future attacks. A case of asthma exacerbation occurring during multiple defecations is reported. Abnormal parasympathetic tone has been implicated in the pathogenesis of certain types of asthma, and defecation can be associated with increased parasympathetic tone. This patient's pattern of defecation-related asthma exacerbations responded to prophylactic anticholinergic medication.

Location of airway inflammation in asthma and the relationship to circadian change in lung function

Nocturnal asthma is an important part of asthma as the majority of patients with asthma have nocturnal worsening in lung function. The etiology of this process is multifactorial and interactive. There are many naturally occurring circadian rhythms, which for the normal individual have only a minor effect on lung function. However, in the asthmatic patient, these day-to-night alterations produce increased airway inflammation and worsening of asthma. Although asthma is considered an airway disease, the location of the inflammatory response may be greater in the alveolar tissue area. If correct, this could alter the therapeutic approach to this disease.

Autonomic regulation in asthmatics with gastroesophageal reflux

STUDY OBJECTIVE

To study the role of autonomic regulation in asthmatics with gastroesophageal reflux (GER).

DESIGN

Prospective study.

SETTING

Autonomic function laboratory of a 908-bed university hospital.

PARTICIPANTS

Fifteen nonsmoking asthmatics with GER (six men, nine women; average age, 36 years).

INTERVENTIONS

Subjects were connected to an ECG monitor. BP was measured by sphygmomanometer at set intervals. After a resting period, each subject had heart rate and BP monitored during an 80 degrees passive tilt, Valsalva maneuver, quiet and deep breathing, handgrip, and an echo stress test of cortical arousal. Each autonomic function test was analyzed and defined as normal, hypervagal, hyperadrenergic, or mixed (a combination of hypervagal and hyperadrenergic responses) as compared with 23 age-matched normal control subjects from our laboratory (14 men, 9 women; average age, 35 years) and published normal control values. Each subject had an overall response score that was determined by the results of the tilt, Valsalva maneuver, and deep breathing maneuvers.

RESULTS

All asthmatics with reflux had at least one autonomic function test display a hypervagal response. Overall response scores show that eight of 15 asthmatics with GER had an overall hypervagal response, and seven had a mixed response. Of the seven asthmatics with GER who had a mixed response score, two had a hypervagal predominant response.

CONCLUSIONS

Asthmatics with GER have evidence of autonomic dysfunction. Heightened vagal tone may be partially responsible for the heightened airway responsiveness to esophageal acidification in asthmatics with reflux.

Cardiovascular autonomic regulation in asthmatic children evidenced by spectral analysis of heart rate and blood pressure variability

The objective of the study was to investigate the features of cardiovascular and respiratory autonomic nervous regulation in asthmatic and control children. Cardiorespiratory reactivity was studied by continuous and non-invasive recording of the electrocardiogram, finger systolic arterial pressure (SAP) and flow-volume spirometry in supine and upright positions and during a deep breathing test in 19 children with bronchial asthma and 10 healthy control children (age 8-11 years). The periodic variability components of R-R intervals (the time between successive heart beats) and SAP in relation to respiration were assessed using spectral analysis techniques. Nine asthmatic children without beta2-agonist medication had a lower respiratory rate and larger high frequency (HF) variability of SAP than the controls, and 10 asthmatic children with beta2-agonist medication had greater low-frequency (LF) variability of SAP and LF/HF ratio of R-R intervals, but their respiratory rate did not differ from the controls. No intergroup differences were found in the postural change of variables. Stable bronchial asthma appears to increase respiratory-induced alterations in systolic blood pressure in children. Beta2-agonist medication, on the other hand, increases sympathetic cardiovascular activity in children with asthma.

Behavioral task-induced bronchodilation in asthma during active and passive tasks: a possible cholinergic link to psychologically induced airway changes

This study investigated pulmonary and autonomic reactions to active and passive behavioral laboratory tasks among asthmatic subjects. It also examined the relationship between airway irritability, as measured by the methacholine challenge test (MCT), and autonomic activity and reactivity to these tasks. Fifty-one asthmatic and 37 nonasthmatic subjects were exposed to psychological laboratory tasks involving either active (mental arithmetic and reaction time) or passive (films depicting shop accidents and thoracic surgery) response. The MCT was given to asthmatics in a separate session. Active tasks reduced respiratory impedance, as measured by forced oscillation pneumography. They also increased heart rate and appeared to block vagal activity, as measured by respiratory sinus arrhythmia (RSA). Airway irritability as assessed by the MCT was positively related to amplitude of RSA and to skin conductance levels. Our data suggest that active and passive behavioral tasks may produce different pulmonary effects among both asthmatic and nonasthmatic individuals. Engaging in tasks requiring active responses may produce temporary improvements in pulmonary function. No autonomic differences were obtained between asthmatics and nonasthmatics in physiological response to stress, but greater cholinergic receptor sensitivity was suggested among high responders to methacholine.

Relation between bronchial and cardiac vagal tone in healthy humans

A generally increased vagal nervous activity was suggested to exist in bronchial asthma; however, this contention has never been fully tested. Before studying vagal activity in asthma, we raised the question if there existed any relation between vagal outflows to different target organs in the physiologic state. The specific aim of this study was to determine the relation between the resting level of bronchial and cardiac vagal activity in healthy volunteers. Bronchial and cardiac vagal tone were measured in 12 subjects as the change of airway resistance (Raw) and heart period (HP) in response to complete cholinergic blockade. It was found that after intravenous atropine administration, Raw was reduced from 1.30 +/- 0.41 cm H2O/L/s to 0.51 +/- 0.22 cm H2O/L/s and HP was reduced from 789 +/- 84 ms to 506 +/- 41 ms. All the values are given as mean +/- SD. Both the bronchial and cardiac responses exhibited considerable interindividual variability, but there was no significant correlation between them (R = 0.22, p = 0.50). It was concluded that under resting conditions, vagal control of bronchial tone and HP were not related in healthy human subjects.

Chronobiology and chronotherapy in medicine

There is a fascinating and exceedingly important area of medicine that most of us have not been exposed to at any level of our medical training. This relatively new area is termed chronobiology; that is, how time-related events shape our daily biologic responses and apply to any aspect of medicine with regard to altering pathophysiology and treatment response. For example, normally occurring circadian (daily cycles, approximately 24 hours) events, such as nadirs in epinephrine and cortisol levels that occur in the body around 10 PM to 4 AM and elevated histamine and other mediator levels that occur between midnight and 4 AM, play a major role in the worsening of asthma during the night. In fact, this nocturnal exacerbation occurs in the majority of asthmatic patients. Because all biologic functions, including those of cells, organs, and the entire body, have circadian, ultradian (less than 22 hours), or infradian (greater than 26 hours) rhythms, understanding the pathophysiology and treatment of disease needs to be viewed with these changes in mind. Biologic rhythms are ingrained, and although they can be changed over time by changing the wake-sleep cycle, these alterations occur over days. However, sleep itself can adversely affect the pathophysiology of disease. The non-light/dark influence of biologic rhythms was first described in 1729 by the French astronomer Jean-Jacques de Mairan. Previously, it was presumed that the small red flowers of the plant Kalanchoe bloss feldiuna opened in the day because of the sunlight and closed at night because of the darkness. When de Mairan placed the plant in total darkness, the opening and closing of the flowers still occurred on its intrinsic circadian basis. It is intriguing to think about how the time of day governs the pathophysiology of disease. On awakening in the morning, heart rate and blood pressure briskly increase, as do platelet aggregability and other clotting factors. This can be linked to the acrophase (peak event) of heart attacks. During the afternoon we hit our best mental and physical performance, which explains why most of us state that "I am not a morning person." Even the tolerance for alcohol varies over the 24-hour cycle, with best tolerance around 5 pm (i.e. "Doctor, I only have a couple of highballs before dinner"). Thus, all biologic functions, from those of the cell, the tissue, the organs, and the entire body, run on a cycle of altering activity and function.(ABSTRACT TRUNCATED AT 400 WORDS)

Decreased heart rate variability in patients with chronic obstructive pulmonary disease

To evaluate possible autonomic nervous system (ANS) dysfunction in patients with chronic obstructive pulmonary disease (COPD) in the absence of any hypoxic neuronal damage, we studied 31 patients with COPD patients aged 31 to 68 years (55 +/- 10) and 32 age-matched healthy subjects (control). Respiratory function in the patients was as follows: FEV1 = 52 +/- 8 percent; PaO2 = 71 +/- 14 mm Hg; and PaCO2 = 40 +/- 10 mm Hg. The ANS was assessed by heart rate variability (HRV) in the time domain (SD of mean RR interval) and frequency domain (autoregressive spectral analysis recognizing low [LF] and high [HF] frequency components, vagal and sympathetic related, respectively). Patients and controls were evaluated at rest and during vagal (controlled breathing [CB]) and sympathetic (passive head-up tilt) maneuvers. Patients with COPD showed a depressed global HRV (rest SD = 34 +/- 20 ms vs 45 +/- 15 ms, p < 0.05; tilt SD = 28 +/- 14 ms vs 38 +/- 13, p < 0.01) with a predominant respiratory drive (rest HF = 44 +/- 28 vs 28 +/- 18, p < 0.05; tilt HF 42 +/- 28 vs 16 +/- 12, p < 0.01) as compared with normal subjects. In the control group, vagal and sympathetic responses were in opposite directions following a stimulus, whereas there was no significant HRV response in the COPD group. We conclude that patients with COPD have abnormalities of ANS function, with in particular a depressed HRV response to sympathetic and vagal stimuli.

Effects of aerosol ipratropium bromide on cardiac vagal tone

Thirty-one adult asthmatic subjects, aged 18 to 40 years, were administered both ipratropium bromide and placebo, in two sessions, held at least 2 days apart, in balanced order. Pulmonary function, heart period (milliseconds between heart beats), and respiratory sinus arrhythmia (a measure of cardiac vagal tone) were assessed before drug administration and 45 min thereafter. Ipratropium bromide had no significant effect on cardiac vagal tone, while it did produce improvement in pulmonary function.

The effects of atropine on respiratory sinus arrhythmia in asthma

Heart rate is rhythmically related to respiratory rate, in a phenomenon known as respiratory sinus arrhythmia (RSA). Amplitude of RSA has been found to be an accurate noninvasive measure of vagal tone in the normal population. The purpose of this study was to examine the relationship between RSA and cardiac vagal tone among asthmatics, a group which has been described as having elevated RSA. This was accomplished by examining the effects of atropine on RSA in asthmatics, and comparing the results to those obtained elsewhere among normal subjects. Atropine at a dose of 1 mg/75 kg body weight was administered to 18 asthmatics, and produced decreases in RSA, equivalent to those previously found among normal subjects. The results suggest that the relationship between cardiac vagal tone and RSA is unaffected by the presence of asthma.

Predictors of the new onset of wheezing among middle-aged and older men. The Normative Aging Study

Characteristics potentially associated with the development of wheeze symptoms were examined in a prospective cohort study of 624 middle-aged and older men who initially denied any history of wheezing or asthma. Initial evaluation included spirometry, methacholine challenge testing, allergy skin testing with common aeroallergens, serum total IgE concentration, blood leukocyte count, blood eosinophil count, and postural heart rate change (standing minus supine). The presence or absence of wheezing symptoms at follow-up 3 yr later was assessed by questionnaire. Multiple logistic regression was used to examine initial characteristics as predictors of subsequent wheezing. Current smoking was the strongest independent predictor of the new onset of wheezing (adjusted OR, 14.3; 95% confidence interval (CI), 3.9 to 52.3). The risk of developing new wheezing also increased with age (adjusted OR, 1.6; 95% CI, 0.9 to 2.9 comparing individual subjects 10 yr apart) and postural heart rate change at the initial examination (adjusted OR, 1.8; 95% CI, 1.1 to 3.0 comparing individual subjects differing by 10 beats/min). A significant association between greater methacholine airway responsiveness (PD20FEV1 < or = 16.8 mumol versus PD20FEV1 > 16.8 mumol) and the subsequent development of wheezing was observed among nonsmokers (adjusted OR, 5.2; 95% CI, 2.0 to 13.6) but not among current smokers. Other baseline variables were not independently related to the risk of developing wheezing symptoms. These data suggest that current smoking, age, nonspecific airway responsiveness, and altered autonomic function are independently related to the risk of developing wheezing symptoms in middle-aged and older men.