Modification of bronchial reactivity by physiological concentrations of plasma epinephrine

Neuromodulation Strategies to Reduce Inflammation and Improve Lung Complications in COVID-19 Patients

Since the outbreak of the COVID-19 pandemic, races across academia and industry have been initiated to identify and develop disease modifying or preventative therapeutic strategies has been initiated. The primary focus has been on pharmacological treatment of the immune and respiratory system and the development of a vaccine. The hyperinflammatory state (“cytokine storm”) observed in many cases of COVID-19 indicates a prognostically negative disease progression that may lead to respiratory distress, multiple organ failure, shock, and death. Many critically ill patients continue to be at risk for significant, long-lasting morbidity or mortality. The human immune and respiratory systems are heavily regulated by the central nervous system, and intervention in the signaling of these neural pathways may permit targeted therapeutic control of excessive inflammation and pulmonary bronchoconstriction. Several technologies, both invasive and non-invasive, are available and approved for clinical use, but have not been extensively studied in treatment of the cytokine storm in COVID-19 patients. This manuscript provides an overview of the role of the nervous system in inflammation and respiration, the current understanding of neuromodulatory techniques from preclinical and clinical studies and provides a rationale for testing non-invasive neuromodulation to modulate acute systemic inflammation and respiratory dysfunction caused by SARS-CoV-2 and potentially other pathogens. The authors of this manuscript have co-founded the International Consortium on Neuromodulation for COVID-19 to advocate for and support studies of these technologies in the current coronavirus pandemic.

Effects of high altitude and cold air exposure on airway inflammation in patients with asthma

AIMS

Eighteen patients with asthma were evaluated during preparation to climb to extreme altitude in order to study the effects of low fractional inspired oxygen (FiO(2)), prolonged exposure to cold air and high altitude on lung function, asthma control and airway inflammation.

METHODS

Spirometry and airway inflammation (fractional exhaled nitric oxide (FeNO) and induced sputum) were studied under different test conditions: hypoxic (FiO(2)=11%) exercise test, 24-hour cold exposure (-5°C) and before, during and after an expedition that involved climbing the Aconcagua mountain (6965 m).

RESULTS

Forced expiratory volume in 1 s (FEV(1)) and FeNO values were slightly lower (p<0.04) after 1 h of normobaric hypoxia. FEV(1) decreased (p=0.009) after 24-hour cold exposure, accompanied by increased sputum neutrophilia (p<0.01). During the expedition FEV(1) and forced vital capacity decreased (maximum FEV(1) decrease of 12.3% at 4300 m) and asthma symptoms slightly increased. After the expedition the Asthma Control Test score and prebronchodilator FEV(1) were reduced (p<0.02), sputum neutrophil count was increased (p=0.04) and sputum myeloperoxidase levels, sputum interleukin 17 mRNA, serum and sputum vascular endothelial growth factor A levels were significantly higher compared with baseline. Patients with asthma with the lowest oxygen saturation during the hypoxic exercise test were more prone to develop acute mountain sickness.

CONCLUSIONS

Exposure to environmental conditions at high altitude (hypoxia, exercise, cold) was associated with a moderate loss of asthma control, increased airway obstruction and neutrophilic airway inflammation. The cold temperature is probably the most important contributing factor as 24-hour cold exposure by itself induced similar effects.

Low voltage vagal nerve stimulation reduces bronchoconstriction in guinea pigs through catecholamine release

OBJECTIVE

  Electrical stimulation of the vagus nerve at relatively high voltages (e.g., >10 V) can induce bronchoconstriction. However, low voltage (≤2 V) vagus nerve stimulation (VNS) can attenuate histamine-invoked bronchoconstriction. Here, we identify the mechanism for this inhibition.

METHODS

  In urethanea-nesthetized guinea pigs, bipolar electrodes were attached to both vagus nerves and changes in pulmonary inflation pressure were recorded in response to i.v. histamine and during VNS. The attenuation of the histamine response by low-voltage VNS was then examined in the presence of pharmacologic inhibitors or nerve ligation.

RESULTS

  Low-voltage VNS attenuated histamine-induced bronchoconstriction (4.4 ± 0.3 vs. 3.2 ± 0.2 cm H(2) O, p < 0.01) and remained effective following administration of a nitric oxide synthase inhibitor, NG-nitro-L-arginine methyl ester, and after sympathetic nerve depletion with guanethidine, but not after the β-adrenoceptor antagonist propranolol. Nerve ligation caudal to the electrodes did not block the inhibition but cephalic nerve ligation did. Low-voltage VNS increased circulating epinephrine and norepinephrine without but not with cephalic nerve ligation.

CONCLUSION

  These results indicate that low-voltage VNS attenuates histamine-induced bronchoconstriction via activation of afferent nerves, resulting in a systemic increase in catecholamines likely arising from the adrenal medulla.

Feasibility of percutaneous vagus nerve stimulation for the treatment of acute asthma exacerbations

OBJECTIVES

This study assessed the feasibility of an investigational vagus nerve stimulation (VNS) device for treating acute asthma exacerbations in patients not responding to at least 1 hour of initial standard care therapy.

METHODS

This was a prospective, nonrandomized study of patients treated in the ED for moderate to severe acute asthma (forced expiratory volume in 1 second [FEV(1)] 25% to 70% of predicted). Treatment entailed percutaneous placement of an electrode near the right carotid sheath and 60 minutes of VNS and continued standard care. VNS voltage was adjusted to perceived improvement, muscle twitching, or adverse events (AEs). All AEs, vital signs, FEV(1), perceived work of breathing (WOB), and final disposition were recorded.

RESULTS

Twenty-five subjects were enrolled. There were no serious AEs and no significant changes in vital signs. No subject required terminating VNS. One patient had minor bleeding from the procedure, and one had a hematoma and withdrew prior to VNS. AEs related to VNS were temporary and included cough (1 of 24), swallowing difficulty (2 of 24), voice change (2 of 24), and muscle twitching (14 of 24). These resolved when VNS ended. The FEV(1) improved at 15 minutes (median = 15.8%, 95% confidence interval [CI] = 9.3% to 22.4%), 30 minutes (median = 21.3%, 95% CI = 8.1% to 36.5%), and 60 minutes (median = 27.5%, 95% CI = 11.3% to 43.5%). WOB improved at 15 minutes (median = 53.9%, 95% CI = 33.7% to 73.9%), 30 minutes (median = 69.1%, 95% CI = 56.4% to 81.8%), and 60 minutes (median = 81.0%, 95% CI = 68.5% to 93.5%).

CONCLUSIONS

Percutaneous VNS did not result in serious AEs and was associated with improvements in FEV(1) and perceived dyspnea. Percutaneous VNS appears to be feasible for use in the treatment of moderate to severe acute asthma in patients unresponsive to initial standard care treatment.

Studying noninvasive indices of vagal control: the need for respiratory control and the problem of target specificity

Respiratory sinus arrhythmia (RSA) is a popular index of cardiac vagal control; however, research has rarely adequately addressed respiratory influences on RSA. In addition, simplistic views of the parasympathetic system have resulted in an overinterpretation of RSA as a general indicator of vagal control. Research using a respiration-corrected time-domain index of RSA has yielded plausible findings that substantially deviate from uncorrected RSA. Paced breathing, which is used for baseline calibration of RSA in this correction procedure, allows for a representative sampling of respiratory influences on RSA and has minimal impact on autonomic regulation. Past research has largely focused on cardiac vagal activity and ignored the extent of target specificity in the parasympathetic system. More research is needed on new noninvasive indices of vagal control at other organ sites. Studies also need to address muscarinic receptor sensitivity before noninvasive vagal indices can be interpreted as markers of central vagal outflow.

Reflex regulation of airway smooth muscle tone

Autonomic nerves in most mammalian species mediate both contractions and relaxations of airway smooth muscle. Cholinergic-parasympathetic nerves mediate contractions, whereas adrenergic-sympathetic and/or noncholinergic parasympathetic nerves mediate relaxations. Sympathetic-adrenergic innervation of human airway smooth muscle is sparse or nonexistent based on histological analyses and plays little or no role in regulating airway caliber. Rather, in humans and in many other species, postganglionic noncholinergic parasympathetic nerves provide the only relaxant innervation of airway smooth muscle. These noncholinergic nerves are anatomically and physiologically distinct from the postganglionic cholinergic parasympathetic nerves and differentially regulated by reflexes. Although bronchopulmonary vagal afferent nerves provide the primary afferent input regulating airway autonomic nerve activity, extrapulmonary afferent nerves, both vagal and nonvagal, can also reflexively regulate autonomic tone in airway smooth muscle. Reflexes result in either an enhanced activity in one or more of the autonomic efferent pathways, or a withdrawal of baseline cholinergic tone. These parallel excitatory and inhibitory afferent and efferent pathways add complexity to autonomic control of airway caliber. Dysfunction or dysregulation of these afferent and efferent nerves likely contributes to the pathogenesis of obstructive airways diseases and may account for the pulmonary symptoms associated with extrapulmonary disorders, including gastroesophageal reflux disease, cardiovascular disease, and rhinosinusitis.

Reflex regulation of airway sympathetic nerves in guinea-pigs

Sympathetic nerves innervate the airways of most species but their reflex regulation has been essentially unstudied. Here we demonstrate sympathetic nerve-mediated reflex relaxation of airway smooth muscle measured in situ in the guinea-pig trachea. Retrograde tracing, immunohistochemistry and electrophysiological analysis identified a population of substance P-containing capsaicin-sensitive spinal afferent neurones in the upper thoracic (T1-T4) dorsal root ganglia (DRG) that innervate the airways and lung. After bilateral vagotomy, atropine pretreatment and pre-contraction of the trachealis with histamine, nebulized capsaicin (10-60 microm) evoked a 63+/-7% reversal of the histamine-induced contraction of the trachealis. Either the beta-adrenoceptor antagonist propranolol (2 microm, administered directly to the trachea) or bilateral sympathetic nerve denervation of the trachea essentially abolished these reflexes (10+/-9% and 6+/-4% relaxations, respectively), suggesting that they were mediated primarily, if not exclusively, by sympathetic adrenergic nerve activation. Cutting the upper thoracic dorsal roots carrying the central processes of airway spinal afferents also markedly blocked the relaxations (9+/-5% relaxation). Comparable inhibitory effects were observed following intravenous pretreatment with neurokinin receptor antagonists (3+/-7% relaxations). These reflexes were not accompanied by consistent changes in heart rate or blood pressure. By contrast, stimulating the rostral cut ends of the cervical vagus nerves also evoked a sympathetic adrenergic nerve-mediated relaxation that were accompanied by marked alterations in blood pressure. The results indicate that the capsaicin-induced reflex-mediated relaxation of airway smooth muscle following vagotomy is mediated by sequential activation of tachykinin-containing spinal afferent and sympathetic efferent nerves innervating airways. This sympathetic nerve-mediated response may serve to oppose airway contraction induced by parasympathetic nerve activation in the airways.

Hormones and breathing

A number of hormones, including hypothalamic neuropeptides acting as neurotransmitters and neuromodulators in the CNS, are involved in the physiologic regulation of breathing and participate in adjustment of breathing in disease. In addition to central effects, some hormones also control breathing at peripheral chemoreceptors or have local effects on the lungs and airways. Estrogen and progesterone seem to protect from sleep-disordered breathing, whereas testosterone may predispose to it. Progesterone and thyroxine have long been known to stimulate respiration. More recently, several hormones such as corticotropin-releasing hormone and leptin have been suggested to act as respiratory stimulants. Somatostatin, dopamine, and neuropeptide Y have a depressing effect on breathing. Animal models and experimental human studies suggest that also many other hormones may be involved in respiratory control.

Handgrip-induced airway dilation in asthmatic patients with bronchoconstriction induced by MCh inhalation

We investigated the effects of static and rhythmic handgrip on the time course of recovery of airway resistance measured with the interrupter technique (Rint) following bronchoconstriction induced by methacholine (MCh) inhalation in 17 asthmatic patients. On three separate occasions, a 100 +/- 5% increase in baseline Rint was induced by MCh inhalation. Subsequently, patients either rested [control trials (CTs)] or performed 3-min bouts of static or rhythmic handgrip. Respiratory and cardiovascular variables were continuously monitored. Rint changes were assessed at 1-min intervals for 30 min after rest and both types of handgrip. Plasma catecholamine concentrations were also determined at scheduled intervals. Bronchoconstriction increased ventilation (P < 0.01) but did not affect cardiovascular variables and plasma catecholamine concentrations. Handgrip provoked an increase in cardiovascular variables (P < 0.01) and plasma norepinephrine concentrations (P < 0.05) but caused no additional changes in ventilation. Rint only partially recovered within 30 min after CTs, whereas it consistently decreased 1 min after both handgrip paradigms and remained lower than after CTs (P always <0.01) for the whole 30-min observation period. Sympathetic activation and withdrawal of cholinergic input to the airway smooth muscle reflexly induced by activation of skeletal muscle and carotid sinus receptors may be the primary events accounting for the bronchodilator response induced by handgrip. Mediators co-released in response to sympathetic activation may also have contributed.

Increased levels of free serotonin in plasma of symptomatic asthmatic patients

BACKGROUND

Previous research has shown that symptomatic asthmatic patients have increased levels of norepinephrine, epinephrine, dopamine, free serotonin, and cortisol in plasma when compared with asymptomatic patients.

OBJECTIVE

We investigated the relationship between plasma levels of catecholamines, free serotonin, and cortisol and clinical status and pulmonary function in symptomatic and asymptomatic patients with asthma.

METHODS

We compared clinical severity, spirometry, and neuroendocrine factors at weeks 0, 1, 2, 3, and 4 in 57 symptomatic (forced expiratory volume in one second [FEV1] < 70%) and 72 asymptomatic (FEV1 > 80%) asthmatic patients. We used multiple analyses of variance (repeated measures) to interpret the data. In addition, we used the Pearson Product Moment Test to investigate correlations among the different variables.

RESULTS

The clinical severity rating and levels of free serotonin, norepinephrine, epinephrine, dopamine, and cortisol were significantly higher in symptomatic asthmatic patients than those in asymptomatic patients (P < .001, in all cases). FEV1 was significantly lower in symptomatic patients than in asymptomatic patients. In symptomatic patients, the level of free serotonin correlated positively with the clinical severity rating (r = .564, P < .01) and negatively with FEV1 (r = -.959, P < .001). In addition, the clinical severity rating showed a negative correlation with FEV1 (r = -.359, P < .01). No significant correlations were found in asymptomatic patients.

CONCLUSION

Our finding that free serotonin was the only neuroendocrine factor closely associated with clinical severity and pulmonary function suggests that this factor plays an important role in the pathophysiology of acute asthma.

Prolonged recovery from exercise-induced asthma with increasing age in childhood

It has been suggested that children with asthma recover more quickly from exercise-induced bronchoconstriction than adults. On the basis of clinical observation we hypothesized that recovery rate from exercise-induced asthma (EIA) in childhood also decreases with age. In 14 children (aged 7-12 years) with a history of EIA, we measured spontaneous recovery from bronchoconstriction induced by two different stimuli: exercise and histamine. The children visited the laboratory three times. After a screening exercise test on the first visit, standardized bronchoprovocation tests with either exercise or histamine were performed on the following two visits in random order. The degree of bronchoconstriction induced by histamine was matched for that observed after exercise. During recovery, forced expiratory volume in 1 second (FEV1) was measured repeatedly up to 2 hours postchallenge. The recovery rate (% increase in FEV1/min) was calculated from the linear slope of the time-response curve. Differences in recovery rate between the two stimuli were analyzed by paired t-test, and age-related differences were analyzed using multiple regression analysis. For the group as a whole, recovery rate was not different between the two stimuli (mean +/- SD: 1.22 +/- 0.91 for exercise, and 1.46 +/- 0.65, for histamine, P = 0.31). However, the recovery rate for exercise-induced bronchoconstriction decreased significantly with age (r = -0.74, P = 0.003), in contrast to the recovery rate for histamine (r = -0.15, P = 0.60). Consequently, in the oldest age group (11-12 years, n = 5) recovery rate from exercise challenge was significantly slower than in the younger age group (7-10 years, n = 9), i.e., 0.54 +/- 0.17 and 1.60 +/- 0.93, respectively, P = 0.009, and slower than the recovery rate from histamine challenge: 0.54 +/- 0.17 and 1.33 +/- 0.54, respectively, P = 0.03. In the younger age group the recovery rates from exercise and histamine were not different (1.60 +/- 0.93 and 1.54 +/- 0.73, respectively, P = 0.83). We conclude that recovery from EIA in childhood decreases with increasing age. These data suggest that the mechanism of exercise-induced asthma in childhood changes with age. This might be due to changes in mediator production or response to mediator release.

Comparison of the effects of salbutamol and adrenaline on airway smooth muscle contractility in vitro and on bronchial reactivity in vivo

BACKGROUND

The effect of adrenergic agonists in asthma depends on their net effect on microvascular leakage, mucosal oedema, vascular clearance of spasmogens, inhibition of cholinergic neurotransmission, and airway smooth muscle contractility. It has been postulated that adrenaline, by virtue of its alpha effects on the vasculature and cholinergic neurotransmission, may have additional useful properties in asthma compared with selective beta agonists such as salbutamol.

METHODS

The airway effects of adrenaline (a non-selective adrenoreceptor agonist) were compared with the selective beta 2 agonist salbutamol. Their airway smooth muscle relaxant potencies and effect on histamine contraction in human bronchi in vitro were compared with their effects on airway calibre and histamine reactivity in asthmatic subjects in vivo. For the in vitro studies changes in tension were measured in response to these agents in thoracotomy specimens of human airways. In vivo the effects of adrenaline and salbutamol on airway calibre and histamine reactivity were measured in eight subjects with mild to moderate asthma in a randomised crossover study.

RESULTS

Salbutamol and adrenaline had approximately equivalent airway smooth muscle relaxant potencies in vitro and bronchodilator potency in vivo. However, their effects on histamine induced contraction in vitro were significantly different from their effects on histamine reactivity in vivo. Salbutamol was less potent in vitro producing a mean (SE) 2.4 (0.15) doubling dose increase in the histamine EC20 and adrenaline a 5.2 (0.18) doubling dose increase (mean difference between salbutamol and adrenaline 2.8 doubling doses; 95% CI 1.1 to 4.5). Salbutamol had no effect on the maximal response to histamine whereas adrenaline reduced it by 54%. In contrast, salbutamol was more potent in vivo producing a mean (SE) increase in PD20 histamine of 1.84 (0.5) doubling doses whereas adrenaline was without effect increasing PD20 by only 0.06 (0.47) doubling doses (mean difference between adrenaline and salbutamol 1.78, 95% CI 0.26 to 3.29 doubling doses).

CONCLUSIONS

These findings suggest that the alpha adrenergic airway effects of non-selective adrenoreceptor agonists such as adrenaline offer no additional protection against histamine-induced broncho-constriction in vivo than beta 2 selective drugs such as salbutamol, despite adrenaline providing greater protection against histamine-induced contraction in vitro. The differences between the effects of these agents in vitro and in vivo may be related to their opposing vascular effects in vivo.