Changes in respiratory sensations induced by lobeline after human bilateral lung transplantation

Hepatocyte CHRNA4 mediates the MASH-promotive effects of immune cell-produced acetylcholine and smoking exposure in mice and humans

Metabolic dysfunction-associated steatohepatitis (MASH) is a leading risk factor for liver cirrhosis and hepatocellular carcinoma. Here, we report that CHRNA4, a subunit of nicotinic acetylcholine receptors (nAChRs), is an accelerator of MASH progression. CHRNA4 also mediates the MASH-promotive effects induced by smoking. Chrna4 was expressed specifically in hepatocytes and exhibited increased levels in mice and patients with MASH. Elevated CHRNA4 levels were positively correlated with MASH severity. We further revealed that during MASH development, acetylcholine released from immune cells or nicotine derived from smoking functioned as an agonist to activate hepatocyte-intrinsic CHRNA4, inducing calcium influx and activation of inflammatory signaling. The communication between immune cells and hepatocytes via the acetylcholine-CHRNA4 axis led to the production of a variety of cytokines, eliciting inflammation in liver and promoting the pathogenesis of MASH. Genetic and pharmacological inhibition of CHRNA4 protected mice from diet-induced MASH. Targeting CHRNA4 might be a promising strategy for MASH therapeutics.

Alterations in Pulmonary Physiology with Lung Transplantation

Lung transplant is a treatment option for patients with end-stage lung diseases; however, survival outcomes continue to be inferior when compared to other solid organs. We review the several anatomic and physiologic changes that result from lung transplantation surgery, and their role in the pathophysiology of common complications encountered by lung recipients. The loss of bronchial circulation into the allograft after transplant surgery results in ischemia-related changes in the bronchial artery territory of the allograft. We discuss the role of bronchopulmonary anastomosis in blood circulation in the allograft posttransplant. We review commonly encountered complications related to loss of bronchial circulation such as allograft airway ischemia, necrosis, anastomotic dehiscence, mucociliary dysfunction, and bronchial stenosis. Loss of dual circulation to the lung also increases the risk of pulmonary infarction with acute pulmonary embolism. The loss of lymphatic drainage during transplant surgery also impairs the management of allograft interstitial fluid, resulting in pulmonary edema and early pleural effusion. We discuss the role of lymphatic drainage in primary graft dysfunction. Besides, we review the association of late posttransplant pleural effusion with complications such as acute rejection. We then review the impact of loss of afferent and efferent innervation from the allograft on control of breathing, as well as lung protective reflexes. We conclude with discussion about pulmonary function testing, allograft monitoring with spirometry, and classification of chronic lung allograft dysfunction phenotypes based on total lung capacity measurements. We also review factors limiting physical exercise capacity after lung transplantation, especially impairment of muscle metabolism. © 2023 American Physiological Society. Compr Physiol 13:4269-4293, 2023.

Dyspnea

The clinical term dyspnea (a.k.a. breathlessness or shortness of breath) encompasses at least three qualitatively distinct sensations that warn of threats to breathing: air hunger, effort to breathe, and chest tightness. Air hunger is a primal homeostatic warning signal of insufficient alveolar ventilation that can produce fear and anxiety and severely impacts the lives of patients with cardiopulmonary, neuromuscular, psychological, and end-stage disease. The sense of effort to breathe informs of increased respiratory muscle activity and warns of potential impediments to breathing. Most frequently associated with bronchoconstriction, chest tightness may warn of airway inflammation and constriction through activation of airway sensory nerves. This chapter reviews human and functional brain imaging studies with comparison to pertinent neurorespiratory studies in animals to propose the interoceptive networks underlying each sensation. The neural origins of their distinct sensory and affective dimensions are discussed, and areas for future research are proposed. Despite dyspnea's clinical prevalence and impact, management of dyspnea languishes decades behind the treatment of pain. The neurophysiological bases of current therapeutic approaches are reviewed; however, a better understanding of the neural mechanisms of dyspnea may lead to development of novel therapies and improved patient care.

Beyond Alkaloids: Novel Bioactive Natural Products From Lobelia Species

In this work, we reviewed the progress in the phytochemical and biological investigations of bioactive components derived from medicinally valuable Lobelia species. In the last 60 years, Lobelia has garnered significant attention from the phytochemist from around the world, majorly due to the discovery of bioactive piperidine alkaloids (e.g., lobinaline and lobeline) in the early 1950s. Later, lobeline underwent clinical trials for several indications including the treatment of attention deficit hyperactivity disorder and a multicenter phase three trial for smoking cessation. Subsequently, several other alkaloids derived from different species of Lobelia were also investigated for their pharmacological characteristics. However, in the last few years, the research focus has started shifting to the characterization of the other novel chemical classes. The major shift has been noticed due to the structurally similar alkaloid components, which essentially share similar pharmacological, physicochemical, and toxicological profiles. In this review, we present an up-to-date overview of their progress with special attention to understanding the molecular mechanisms of the novel bioactive components.

Air Hunger: A Primal Sensation and a Primary Element of Dyspnea

The sensation that develops as a long breath hold continues is what this article is about. We term this sensation of an urge to breathe "air hunger." Air hunger, a primal sensation, alerts us to a failure to meet an urgent homeostatic need maintaining gas exchange. Anxiety, frustration, and fear evoked by air hunger motivate behavioral actions to address the failure. The unpleasantness and emotional consequences of air hunger make it the most debilitating component of clinical dyspnea, a symptom associated with respiratory, cardiovascular, and metabolic diseases. In most clinical populations studied, air hunger is the predominant form of dyspnea (colloquially, shortness of breath). Most experimental subjects can reliably quantify air hunger using rating scales, that is, there is a consistent relationship between stimulus and rating. Stimuli that increase air hunger include hypercapnia, hypoxia, exercise, and acidosis; tidal expansion of the lungs reduces air hunger. Thus, the defining experimental paradigm to evoke air hunger is to elevate the drive to breathe while mechanically restricting ventilation. Functional brain imaging studies have shown that air hunger activates the insular cortex (an integration center for perceptions related to homeostasis, including pain, food hunger, and thirst), as well as limbic structures involved with anxiety and fear. Although much has been learned about air hunger in the past few decades, much remains to be discovered, such as an accepted method to quantify air hunger in nonhuman animals, fundamental questions about neural mechanisms, and adequate and safe methods to mitigate air hunger in clinical situations. © 2021 American Physiological Society. Compr Physiol 11:1449-1483, 2021.

Dyspnea related to reversibly-binding P2Y12 inhibitors: A review of the pathophysiology, clinical presentation and diagnostics

Dyspnea is a common symptom physiologically associated with strenuous exercise and pathologically reflecting well-known diseases and conditions that are predominantly pulmonary, cardiovascular, and weight-related in origin. Dyspnea improves with appropriate measures that enhance physical performance and treatment of the underlying diseases. Dyspnea is less commonly triggered by other causes such as the environment (e.g., ozone), drugs, and others, some of which do not seem to affect bronchopulmonary function as evidenced by normal results of comprehensive pulmonary function testing. In cardiovascular medicine, dyspnea has recently attracted attention because it has been reported that this symptom occurs more frequently with the administration of the new oral reversibly-binding platelet P2Y12 receptor inhibitors ticagrelor [1-6], cangrelor [7-10], and elinogrel [11]. This paper succinctly addresses the current understanding of the pathophysiology, clinical presentation, and diagnostics of dyspnea, associated either with bronchopulmonary function impairment, as triggered mainly by pulmonary and cardiovascular diseases, or without bronchopulmonary function impairment, as induced by endogenous or external compounds such as drugs in order to provide a context for understanding, recognizing and managing P2Y12 inhibitor-induced dyspnea.

Inspiratory high frequency airway oscillation attenuates resistive loaded dyspnea and modulates respiratory function in young healthy individuals

Direct chest-wall percussion can reduce breathlessness in Chronic Obstructive Pulmonary Disease and respiratory function may be improved, in health and disease, by respiratory muscle training (RMT). We tested whether high-frequency airway oscillation (HFAO), a novel form of airflow oscillation generation can modulate induced dyspnoea and respiratory strength and/or patterns following 5 weeks of HFAO training (n = 20) compared to a SHAM-RMT (conventional flow-resistive RMT) device (n = 15) in healthy volunteers (13 males; aged 20–36 yrs). HFAO causes oscillations with peak-to-peak amplitude of 1 cm H₂O, whereas the SHAM-RMT device was identical but created no pressure oscillation. Respiratory function, dyspnoea and ventilation during 3 minutes of spontaneous resting ventilation, 1 minute of maximal voluntary hyperventilation and 1 minute breathing against a moderate inspiratory resistance, were compared PRE and POST 5-weeks of training (2×30 breaths at 70% peak flow, 5 days a week). Training significantly reduced NRS dyspnoea scores during resistive loaded ventilation, both in the HFAO (p = 0.003) and SHAM-RMT (p = 0.005) groups. Maximum inspiratory static pressure (cm H₂O) was significantly increased by HFAO training (vs. PRE; p<0.001). Maximum inspiratory dynamic pressure was increased by training in both the HFAO (vs. PRE; p<0.001) and SHAM-RMT (vs. PRE; p = 0.021) groups. Peak inspiratory flow rate (L.s⁻¹) achieved during the maximum inspiratory dynamic pressure manoeuvre increased significantly POST (vs. PRE; p = 0.001) in the HFAO group only. HFAO reduced inspiratory resistive loading–induced dyspnoea and augments static and dynamic maximal respiratory manoeuvre performance in excess of flow-resistive IMT (SHAM-RMT) in healthy individuals without the respiratory discomfort associated with RMT.

Sprouted innervation into uterine transplants contributes to the development of hyperalgesia in a rat model of endometriosis

Endometriosis is an enigmatic painful disorder whose pain symptoms remain difficult to alleviate in large part because the disorder is defined by extrauteral endometrial growths whose contribution to pain is poorly understood. A rat model (ENDO) involves autotransplanting on abdominal arteries uterine segments that grow into vascularized cysts that become innervated with sensory and sympathetic fibers. ENDO rats exhibit vaginal hyperalgesia. We used behavioral, physiological, and immunohistochemical methods to test the hypothesis that cyst innervation contributes to the development of this hyperalgesia after transplant. Rudimentary sensory and sympathetic innervation appeared in the cysts at two weeks, sprouted further and more densely into the cyst wall by four weeks, and matured by six weeks post-transplant. Sensory fibers became abnormally functionally active between two and three weeks post-transplant, remaining active thereafter. Vaginal hyperalgesia became significant between four and five weeks post-transplant, and stabilized after six to eight weeks. Removing cysts before they acquired functional innervation prevented vaginal hyperalgesia from developing, whereas sham cyst removal did not. Thus, abnormally-active innervation of ectopic growths occurs before hyperalgesia develops, supporting the hypothesis. These findings suggest that painful endometriosis can be classified as a mixed inflammatory/neuropathic pain condition, which opens new avenues for pain relief. The findings also have implications beyond endometriosis by suggesting that functionality of any transplanted tissue can be influenced by the innervation it acquires.

An official American Thoracic Society statement: update on the mechanisms, assessment, and management of dyspnea

BACKGROUND

Dyspnea is a common, distressing symptom of cardiopulmonary and neuromuscular diseases. Since the ATS published a consensus statement on dyspnea in 1999, there has been enormous growth in knowledge about the neurophysiology of dyspnea and increasing interest in dyspnea as a patient-reported outcome.

PURPOSE

The purpose of this document is to update the 1999 ATS Consensus Statement on dyspnea.

METHODS

An interdisciplinary committee of experts representing ATS assemblies on Nursing, Clinical Problems, Sleep and Respiratory Neurobiology, Pulmonary Rehabilitation, and Behavioral Science determined the overall scope of this update through group consensus. Focused literature reviews in key topic areas were conducted by committee members with relevant expertise. The final content of this statement was agreed upon by all members.

RESULTS

Progress has been made in clarifying mechanisms underlying several qualitatively and mechanistically distinct breathing sensations. Brain imaging studies have consistently shown dyspnea stimuli to be correlated with activation of cortico-limbic areas involved with interoception and nociception. Endogenous and exogenous opioids may modulate perception of dyspnea. Instruments for measuring dyspnea are often poorly characterized; a framework is proposed for more consistent identification of measurement domains.

CONCLUSIONS

Progress in treatment of dyspnea has not matched progress in elucidating underlying mechanisms. There is a critical need for interdisciplinary translational research to connect dyspnea mechanisms with clinical treatment and to validate dyspnea measures as patient-reported outcomes for clinical trials.

An official American Thoracic Society statement: update on the mechanisms, assessment, and management of dyspnea

BACKGROUND

Dyspnea is a common, distressing symptom of cardiopulmonary and neuromuscular diseases. Since the ATS published a consensus statement on dyspnea in 1999, there has been enormous growth in knowledge about the neurophysiology of dyspnea and increasing interest in dyspnea as a patient-reported outcome.

PURPOSE

The purpose of this document is to update the 1999 ATS Consensus Statement on dyspnea.

METHODS

An interdisciplinary committee of experts representing ATS assemblies on Nursing, Clinical Problems, Sleep and Respiratory Neurobiology, Pulmonary Rehabilitation, and Behavioral Science determined the overall scope of this update through group consensus. Focused literature reviews in key topic areas were conducted by committee members with relevant expertise. The final content of this statement was agreed upon by all members.

RESULTS

Progress has been made in clarifying mechanisms underlying several qualitatively and mechanistically distinct breathing sensations. Brain imaging studies have consistently shown dyspnea stimuli to be correlated with activation of cortico-limbic areas involved with interoception and nociception. Endogenous and exogenous opioids may modulate perception of dyspnea. Instruments for measuring dyspnea are often poorly characterized; a framework is proposed for more consistent identification of measurement domains.

CONCLUSIONS

Progress in treatment of dyspnea has not matched progress in elucidating underlying mechanisms. There is a critical need for interdisciplinary translational research to connect dyspnea mechanisms with clinical treatment and to validate dyspnea measures as patient-reported outcomes for clinical trials.

Effects of preconditioning on the resistance to acute hypobaric hypoxia and their correction with selective antagonists of nicotinic receptors

Hypobaric hypoxic preconditioning increased the resistance of low resistant and highly resistant rats to acute hypobaric hypoxia at a critical height. Intergroup differences in the resistance of rats to acute hypobaric hypoxia were not observed after hypobaric hypoxia and one variational series with a wide range of resistance (4.5-24.5 min) appeared. Methyllycaconitine, an antagonist of subtype α(7) nicotinic cholinergic receptors, abolished the influence of hypobaric hypoxia on low resistant rats, but had no effect on highly resistant animals. Mecamylamine, a preferential antagonist of subtype α(4)β(2) and α(3)-containing cholinergic receptors, did not modulate the effect of hypobaric hypoxia. By contrast, hypobaric hypoxia abolished the effect of mecamylamine on the resistance of rats that were not trained under conditions of hypobaric hypoxia (low resistant and highly resistant animals with low sensitivity to hypobaric hypoxia). We conclude that the same effect of hypobaric hypoxia is mediated by various mechanisms, which involve different nicotinic cholinergic receptors. They differ from the resistance mechanisms in non-trained rats.

Cough reflex in lung transplant recipients

Lung transplantation has become the standard of care for particular individuals with advanced lung disease. However, this surgical procedure involves interruption of the lower vagal nerve fibers which leads to loss of the protective cough reflex. Injury of the neural pathways involved with the sensory limb of the cough reflex is associated with an increased risk of complications involving the allograft. While loss of the cough reflex was once considered permanent, recent evidence indicates functional and structural restoration is a time-dependent process that occurs 6-12 months after lung transplantation. The implication that the cough reflex may be reestablished in lung transplant recipients provides insight into the dynamic response to airway neural injury that may lead to improvements in allograft tissue repair.

Lung transplantation and lung volume reduction surgery

Since the publication of the last edition of the Handbook of Physiology, lung transplantation has become widely available, via specialized centers, for a variety of end-stage lung diseases. Lung volume reduction surgery, a procedure for emphysema first conceptualized in the 1950s, electrified the pulmonary medicine community when it was rediscovered in the 1990s. In parallel with their technical and clinical refinement, extensive investigation has explored the unique physiology of these procedures. In the case of lung transplantation, relevant issues include the discrepant mechanical function of the donor lungs and recipient thorax, the effects of surgical denervation, acute and chronic rejection, respiratory, chest wall, and limb muscle function, and response to exercise. For lung volume reduction surgery, there have been new insights into the counterintuitive observation that lung function in severe emphysema can be improved by resecting the most diseased portions of the lungs. For both procedures, insights from physiology have fed back to clinicians to refine patient selection and to scientists to design clinical trials. This section will first provide an overview of the clinical aspects of these procedures, including patient selection, surgical techniques, complications, and outcomes. It then reviews the extensive data on lung and muscle function following transplantation and its complications. Finally, it reviews the insights from the last 15 years on the mechanisms whereby removal of lung from an emphysema patient can improve the function of the lung left behind.

Targeting peripheral afferent nerve terminals for cough and dyspnea

Chronic unproductive coughing and dyspnea are symptoms that severely diminish the quality of life in a substantial proportion of the population. There are presently few if any drugs that effectively treat these symptoms. Rational drug targets for cough and dyspnea have emerged over the recent years based on developments in our understanding of the innervation of the respiratory tract. These drug targets can be subcategorized into those that target the vagal afferent nerve endings, and those that target neural activity within the CNS. This review focuses on targets presumed to be in the peripheral terminals of afferent nerves within the airways. Conceptually, the activity of peripheral afferent nerves involved with unwanted urge-to-cough or dyspnea sensations can be inhibited by limiting the intensity of the stimulus, inhibiting the amplitude of the stimulus-induced generator potential, or inhibiting the transduction between the generator potential and action potential discharge and conduction. These mechanisms reveal many therapeutic strategies for anti-tussive and anti-dyspnea drug development with peripheral sites of action.

Chronic 'cough hypersensitivity syndrome': a more precise label for chronic cough

Chronic cough remains a challenge to many clinicians because there is often no diagnostic link to causation, and because indirect antitussives are largely ineffective. Chronic cough can also be a predominant symptom associated with many chronic respiratory diseases such as COPD, asthma and pulmonary fibrosis. Chronic cough itself does impair the quality of life and is associated with psychological impairment. The symptoms associated with chronic cough include persistent tickling or irritating sensation in the chest or throat, hoarse voice, dysphonia or vocal cord dysfunction. Currently, the clinical diagnosis of cough is associated with chronic cough caused by airway eosinophilic conditions such as asthma, gastrooesophageal reflux disease or post-nasal drip (or upper airway syndrome), which implies cause and effect, or with chronic cough associated with other diseases such as COPD, cancer or heart failure, that does not necessarily imply cause and effect. A recently-recognised category is idiopathic cough, with no associated or causative diagnosis. We suggest that there is a better label needed for chronic cough, that includes the common association with a hypersensitive cough response to tussive stimuli such as capsaicin or citric acid. This would invoke a hypersensitive syndrome, and there are good reasons to use a new label that would encompass the problem of chronic cough: the chronic 'cough hypersensitivity syndrome'. This would focus the problem on the cough symptomatology and lead to greater focus on understanding the mechanisms of cough sensitisation, with the ultimate aim of obtaining more effective antitussives.

Mechanisms of dyspnea

The mechanisms and pathways of the sensation of dyspnea are incompletely understood, but recent studies have provided some clarification. Studies of patients with cord transection or polio, induced spinal anesthesia, or induced respiratory muscle paralysis indicate that activation of the respiratory muscles is not essential for the perception of dyspnea. Similarly, reflex chemostimulation by CO₂ causes dyspnea, even in the presence of respiratory muscle paralysis or cord transection, indicating that reflex chemoreceptor stimulation per se is dyspnogenic. Sensory afferents in the vagus nerves have been considered to be closely associated with dyspnea, but the data were conflicting. However, recent studies have provided evidence of pulmonary vagal C-fiber involvement in the genesis of dyspnea, and recent animal data provide a basis to reconcile differences in responses to various C-fiber stimuli, based on the ganglionic origin of the C fibers. Brain imaging studies have provided information on central pathways subserving dyspnea: Dyspnea is associated with activation of the limbic system, especially the insular area. These findings permit a clearer understanding of the mechanisms of dyspnea: Afferent information from reflex stimulation of the peripheral sensors (chemoreceptors and/or vagal C fibers) is processed centrally in the limbic system and sensorimotor cortex and results in increased neural output to the respiratory muscles. A perturbation in the ventilatory response due to weakness, paralysis, or increased mechanical load generates afferent information from vagal receptors in the lungs (and possibly mechanoreceptors in the respiratory muscles) to the sensorimotor cortex and results in the sensation of dyspnea.

Future directions in treating cough

Cough is a common and troublesome symptom that can be difficult to treat. New therapeutic options that are safe and more effective than those currently available are needed. In this article, the authors offer opinion on future directions in the treatment of cough, with a particular emphasis on the clinical syndrome associated with cough reflex hypersensitivity. In addition, the article provides an overview of some of the diagnostic technologies and promising drug targets likely to emerge from current clinical and scientific endeavor.

Blockade of airway sensory nerves and dyspnea in humans

Evidence has accumulated from previous studies that vagal fibers in the lungs are involved in the genesis of dyspnea. In a series of human studies, based on our previous animal data (J Physiol 1998; 508:109-18; J Appl Physiol 1998; 84:417-24; J Appl Physiol 2003; 95:1315-24) we established that intravenous adenosine has a dyspnogenic effect (J Appl Physiol 2005; 98:180-5; Respir Res 2006; 7:139; Pulm Pharmacol Ther 2008; 21:208-13), strongly implicating a role for vagal C-fibers in the genesis of dyspnea. We have now analyzed the relative effects of blockade of vagal C-fibers by two methods and routes of delivery: by inhibition of the sodium channel and interruption of action potential conduction in the nerve by inhaled local anesthetic (lidocaine), and by blockade by systemic theophylline, a known, nonselective adenosine receptor antagonist. Both techniques significantly (p < 0.05) attenuated the dyspneic response to intravenous adenosine. However, the attenuation was significantly (p < 0.05) greater with pretreatment with systemic theophylline (mean change in response, DeltaAUC -44%) versus pretreatment with inhaled lidocaine (mean change in response, DeltaAUC -11.8%). These differences in the results of airway sensory nerve blockade probably reflect different populations of C fiber receptors and may explain conflicting results of previous studies of dyspnea and airway anesthesia.

Fog-induced Cough with Impaired Respiratory Sensation in Congenital Central Hypoventilation Syndrome

RATIONALE

Congenital central hypoventilation syndrome (CCHS) is a genetic disorder mainly characterized by failure of automatic control of breathing, causing alveolar hypoventilation. Little is known regarding cough in CCHS. Parental reports indicate that patients cough normally during airway infections; however, previous studies have demonstrated no cough response to fog inhalation.

OBJECTIVES

To evaluate the sensory and motor components of cough, respiratory sensations, and changes in ventilation evoked by fog inhalation in children with CCHS and in sex- and age-matched control subjects.

METHODS

Cough threshold was measured and cough intensity was indexed in terms of cough peak expiratory flow and integrated abdominal electromyographic activity. The pattern of breathing was recorded by inductive plethysmography. Respiratory sensations were also investigated.

MEASUREMENTS AND MAIN RESULTS

All control subjects and six of seven patients coughed in response to fog inhalation. The seventh coughed with citric acid aerosol inhalation. Cough threshold values were similar in control subjects (range, 0.40-2.22 ml/min) and patients (range, 0.40-3.26 ml/min). Mean values of cough peak expiratory flow and of integrated abdominal electromyographic activity-related variables during coughing were also similar and corresponded to 80% of those recorded during maximum voluntary cough. Cough appearance was preceded by respiratory sensations and increases (P < 0.01) in ventilation in the control subjects but not in the patients.

CONCLUSIONS

Children with CCHS have normal cough threshold and motor responses to fog inhalation. However, the lack of respiratory sensations and the likely related ventilatory changes typically elicited by tussigenic fog concentrations suggest a neural sensory deficit that may increase the risk of respiratory disease in these patients.

Motor and sensory re-innervation of the lung and heart after re-anastomosis of the cervical vagus nerve in rats

There is no study in the literature dealing with re-innervation of the cardiopulmonary vagus nerve after its transection followed by re-anastomosis. In the present study, we explored the bronchomotor, heart rate and respiratory responses in rats at 2, 3 and 6 months after re-anastomosis of one cervical vagus trunk. The conduction velocity of A, B and C waves was calculated in the compound vagal action potential. We searched for afferent vagal activities in phase with pulmonary inflation to assess the persistence of pulmonary stretch receptor (PSR) discharge in re-innervated lungs. In each animal, data from the stimulation or recording of one re-anastomosed vagus nerve were compared with those obtained in the contra-lateral intact one. Two and three months after surgery, the conduction velocities of A and B waves decreased, but recovery of conduction velocity was complete at 6 months. By contrast, the conduction velocity of the C wave did not change until 6 months, when it was doubled. The PSR activity was present in 50% of re-anastomosed vagus nerves at 2 and 3 months and in 75% at 6 months. Respiratory inhibition evoked by vagal stimulation was significantly weaker from the re-anastomosed than intact nerve at 2 but not 3 months. Vagal stimulation did not elicit cardiac slowing or bronchoconstriction 6 months after re-anastomosis. Our study demonstrates the capacity of pulmonary vagal sensory neurones to regenerate after axotomy followed by re-anastomosis, and the failure of the vagal efferents to re-innervate both the lungs and heart.

Cough and ventilatory adjustments evoked by aerosolised capsaicin and distilled water (fog) in man

Airway receptors mediate cough and ventilatory adjustments. Simultaneous assessment of cough sensory-motor components and changes in breathing pattern may provide insights into the receptor(s) prevailingly stimulated by inhaled irritants. Nineteen subjects inhaled capsaicin and fog up to threshold concentrations for cough. Cough intensity, respiratory sensations and changes in breathing pattern induced by the two irritants were compared. Capsaicin and fog cough threshold values did not correlate. Coughing induced by both agents was preceded by qualitatively similar sensations and by significant increases in minute ventilation and respiratory drive due to selective increases in tidal volume (P<0.01). Cough intensity was similar with both agents. Cough frequency and the intensity of the urge to cough were higher with capsaicin (P<0.01). The lack of correlation between fog and capsaicin cough threshold values suggests differences in the neural mechanisms activated. The selective increase in tidal volume suggests prevailing involvement of rapidly adapting receptors. The stronger sensations evoked by capsaicin may contribute to the higher cough frequency observed with this agent.

The role of vagal afferent nerves in chronic obstructive pulmonary disease

Circumstantial evidence supports the hypothesis that the vagal nervous system is dysregulated in chronic obstructive pulmonary disease. This dysregulation can lead to an increased sensitivity of the cough reflex such that the coughing becomes, at times, "nonproductive" or inappropriate. Vagal dysregulation can also lead to an increase in the activity of the parasympathetic reflex control of the airways, which contributes to greater mucus secretion and bronchial smooth muscle contraction. Indirect evidence indicates that lung disease is accompanied by substantive changes to the entire reflex pathways, including enhanced activity of the primary afferent nerves, increases in synaptic efficacy at secondary nerves in the central nervous system, and changes in the autonomic nerve pathways. Drugs aimed at normalizing neuronal activity may, therefore, be beneficial in chronic obstructive pulmonary disease.

How does lobeline injected intravenously produce a cough?

In order to examine, whether the lobeline-induced cough is a true reflex or a voluntary effort to get rid of its irritating sensations in the upper respiratory tract, we systematically studied the cough response to lobeline, of subjects who were unable to make conscious discriminations i.e. were either comatose (n=4) or anaesthetized (n=5). 8 microg/kg lobeline injected into the right atrium of one and 29 microg/kg intravenously (i.v.) into another evenly and spontaneously breathing comatose subject produced a cough after 4s and 12s, respectively. Cough was repeatable and showed a dose response relationship i.e., its latency decreasing and its duration/intensity increasing with the dose. In a third subject, capable only of weak spontaneous respiration, a relatively high dose injected into the right atrium (44 microg/kg) generated a pronounced cough-like respiratory movement superimposed on the artificial ventilation and also during the apnoea after disconnecting the pump. No respiratory response was evoked in a fourth subject who had no evidence of brainstem reflexes. In five normals, cough was elicited with a mean dose of 35+/-5 microg/kg i.v. (latency 14+/-2 s; duration 10+/-3 s). After thiopental anaesthesia, injecting 41+/-7 microg/kg produced a cough within 13+/-2 s that lasted for 12+/-2 s. It may be noted that neither the later dose nor the latency or duration of cough that it produced were significantly different from the pre anaesthesia values (P>0.05). These two sets of results show unequivocally that the lobeline-induced cough is evoked reflexly; its magnitude in the conscious state could vary by subjective influences. We discuss the likelihood of its origin from juxtapulmonary capillary receptors.

Presence of lobeline-like sensations in exercising patients with left ventricular dysfunction

Since there is evidence that lobeline-induced sensations, associated with discomfort in the mouth, throat and chest arise by stimulating juxtapulmonary or J receptors, we were interested in investigating if similar sensations are felt by patients with left ventricular dysfunction (LVD) in whom a natural stimulation of these receptors would occur by transient interstitial oedema or during augmentation of the stimulus, by increased pulmonary blood flow during exercise. Threshold doses of lobeline produced three or more respiratory sensations simultaneously in 9 out of 10 patients, which was greater than the response of the controls (P < 0.01). With mild exercise, a greater number of patients (7) than controls (1) reported feeling two or more sensations (P < 0.01); in fact half the controls did not express a respiratory sensation with equivalent exercise (P < 0.05). The predominant lobeline-like sensations reported by patients with exercise were a feeling of heat or burning and pressure in the throat or chest (P < 0.05). The presence of cough in three patients and in none of the controls was noteworthy. The mean latency with which sensations appeared during exercise in patients (4.4 +/- 0.3 min) was almost half that in controls (7.4 +/- 0.2 min) (P < 0.005). Since, respiratory sensations in response to lobeline and exercise were intensified in patients compared to controls and since both lobeline and exercise-induced sensations were similar (P < 0.05), we speculate that a common origin exists. Despite important caveats, that we discuss, in our view these respiratory sensations and cough arise from stimulation of J receptors.

Role of sensory input from the lungs in control of muscle sympathetic nerve activity during and after apnea in humans

We reasoned that, if the lung inflation reflex contributes importantly to apnea-induced sympathetic activation, such activation would be attenuated in bilateral lung transplant recipients (LTX). We measured muscle sympathetic nerve activity (MSNA; intraneural electrodes), heart rate, mean arterial pressure, tidal volume, end-tidal Pco(2), and arterial oxygen saturation in seven LTX and seven healthy control subjects (Con) before, during, and after 20-s end-expiratory breath holds. Our evidence for denervation in LTX was 1) greatly attenuated respiratory sinus arrhythmia and 2) absence of cough reflex below the level of the carina. During apnea, the temporal pattern and the peak increase in MSNA were virtually identical in LTX and Con (347 +/- 99 and 359 +/- 46% of baseline, respectively; P > 0.05). In contrast, the amount of MSNA present in the first 5 s after resumption of breathing was greater in LTX vs. Con (101 +/- 4 vs. 38 +/- 7% of baseline, respectively; P < 0.05). There were no between-group differences in apnea-induced hypoxemia or hypercapnia, hemodynamic, or ventilatory responses. Thus cessation of the rhythmic sympathoinhibitory feedback that normally accompanies eupneic breathing does not contribute importantly to sympathetic excitation during apnea. In contrast, vagal afferent input elicited by hyperventilation-induced lung stretch plays an important role in the profound, rapid sympathetic inhibition that occurs after resumption of breathing after apnea.

Magnitude estimation of inspiratory resistive loads by double-lung transplant recipients

The purpose of this study was to investigate the role of afferent input from the lung and lower airways in magnitude estimation of inspiratory resistive loads (R). To assess the role of lung vagal afferents in respiratory sensation, sensations related to inspiratory R, reflected by subjects' percentage of handgrip responses (HG%), were compared between double-lung transplant (DLT) recipients with normal lung function and healthy control (Nor) subjects. Perceptual sensitivity to the external load was measured as the slope of HG% as a function of peak mouth pressure (Pm), and the slope of HG% as a function of R, after a log-log transformation. The results showed that the DLT group had a similar HG% response, as well as the slopes of log HG%-log Pm and log HG%-log R, compared with the Nor group. Furthermore, the ventilatory responses to external loads were also similar between the two groups. These results suggest that lung vagal afferents do not play a significant role in magnitude estimation of inspiratory resistive loads in humans.

Detection of inspiratory resistive loads in double-lung transplant recipients

The afferent pathways mediating respiratory load perception are still largely unknown. To assess the role of lung vagal afferents in respiratory sensation, detection of inspiratory resistive loads was compared between 10 double-lung transplant (DLT) recipients with normal lung function and 12 healthy control (Nor) subjects. Despite a similar unloaded and loaded breathing pattern, the DLT group had a significantly higher detection threshold (2.91 +/- 0.5 vs. 1.55 +/- 0.3 cmH(2)O. l(-1). s) and Weber fraction (0.50 +/- 0.1 vs. 0.30 +/- 0.1) compared with the Nor group. These results suggest that inspiratory resistive load detection occurs in the absence of vagal afferent feedback from the lung but that lung vagal afferents contribute to inspiratory resistive load detection response in humans. Lung vagal afferents are not essential to the regulation of resting breathing and load compensation responses.

Respiratory-related evoked potentials elicited by inspiratory occlusions in double-lung transplant recipients

This study investigated the role of lung vagal afferents in the respiratory-related evoked potential (RREP) response to inspiratory occlusions by using double-lung transplant recipients as a lung denervation model. Evoked potential recordings in response to inspiratory occlusions were obtained from 10 double-lung transplant (DLT) recipients with normal lung function and 12 healthy control (Nor) subjects under the attend, ignore, and unoccluded conditions. Results demonstrated that early-latency RREP components (P(1), P(1a), N(f), and N(1)) were not significantly different between the DLT and the Nor groups. The late-latency RREP component (P(3)) was identifiable in all DLT subjects during the attend trial. However, P(3) latency was significantly longer in the DLT group compared with the Nor group. The zero-to-peak amplitude of P(3) was also significantly smaller in the DLT group than that in the Nor group during the attend trial. These results suggest that lung vagal afferents were not essential to elicit RREP responses, but may contribute to the cognitive processing of respiratory stimuli.

Balancing acts: respiratory sensations, motor control and human posture

1. The present brief review covers some novel aspects of integration between respiration and movement of the body. 2. There are potent viscerosomatic reflexes in animals involving small-diameter pulmonary afferents that, when excited, would limit exercise. However, recent studies using lobeline injections to excite pulmonary afferents in awake humans suggest that there is no evoked reflex motoneuronal inhibition. Instead, the noxious respiratory sensations generated by the vagal afferents may be crucial in the decision to stop exercise. 3. While respiratory movements may affect limb movements, the control of the trunk and limbs can involve interaction (and even interference) with key respiratory muscles, such as the diaphragm. Recent studies have revealed that not only does the diaphragm receive feed-forward drive prior to some limb movements, but that it also contracts both phasically and tonically during repetitive limb movements. 4. Thus, challenges to posture can indirectly challenge ventilation, while coordinated diaphragm contraction may contribute to control of the trunk.