Influence Of Chemoreceptors Research Articles

Intermittent hypoxia: keeping it real

in this issue of the Journal of Applied Physiology , Tamisier and colleagues ([20][1]) describe a novel method for studying the effects of chronic intermittent hypoxia (CIH) in healthy human subjects. To investigate the effects of CIH on sleep, ventilatory control, and blood pressure, the authors

NO and CO have got to GO for enhanced chemoreceptor sympathoexcitation in heart failure

arterial chemoreceptors located in the carotid body are an important defense mechanism against systemic hypoxemia. Activation of arterial chemoreceptors increases alveolar ventilation and sympathetic outflow to most vascular beds. During acute exposures to hypoxia, the sympathoexcitatory responses

6 Anaesthesia and the respiratory system in paediatrics

Summary This article is an overview of the paediatric respiratory system and its importance for anaesthesia. Differences between paediatric and adult lung volumes and age-dependent respiratory variables exist. The efficiency of the pulmonary network is demonstrated in the alveolar ventilation and pulmonary perfusion relationships, or the V/Q matching. The control of breathing is largely determined by the central and peripheral chemoreceptors. The breathing system depends on the anatomy of the airway for efficiency. The pulmonary system effectively integrates the alveolar-capillary gas exchange, the physics of gas flow, restrictive forces, and surface tension, as well as extrapulmonary factors such as neuronal control from the higher respiratory centre and central and peripheral chemoreceptor influences. In this article, we discuss the embryological development of the lung, the fetal circulation, the perinatal changes of the fetal circulation and respiratory system, and the pulmonary mechanics of the neonate and child. The oxygen and carbon dioxide gas-exchange relationship and its effects on V/Q matching are discussed. The neuronal control of breathing in regard to central and peripheral chemoreceptors is elaborated. The acquired and congenital airway abnormalities of the neonate and child are described. Examples of the differences between neonatal, childhood and adult airways are emphasized. The abnormal and difficult airways are discussed in regards to the anaesthetic considerations. We use the heavily debated issue of the presence preoperatively of upper respiratory infections (URIs) to illustrate the difficult dilemmas posed in deciding whether or not to provide general anaesthesia when the risk of intraoperative complications is increased. Specific congenital airway abnormalities are associated with difficult endotracheal intubation. Neonatal abnormalities such as tracheoesophageal fistula, congenital diaphragmatic hernia, and persistent pulmonary hypertension of the newborn are discussed in detail. This article also covers chronic pulmonary diseases such as cystic fibrosis, asthma, sleep apnoea, and bronchopulmonary dysplasia which all present potential challenges for the anaesthetist. We also note important factors in monitoring of the neonate and child are to evaluate oxygenation and ventilation. We provide examples of the effects of anaesthesia on respiratory variables, carbon dioxide and oxygen responses, and airway anatomy.

Vagal and chemoreceptor influences on abdominal muscle activity in awake lambs during hypoxia.

The ventilatory response to hypoxia is a complex phenomenon involving several control mechanisms. We designed this study to examine the dynamic control of abdominal muscle expiratory electromyogram (EMG) activity during room-air breathing and hypoxia and then to analyze the relative contribution of the chemoreceptors and vagal afferents. We studied 12 11- to 22-day-old awake nonsedated lambs, six intact and six vagotomized. To assess the dynamic influence of peripheral chemoreceptors on abdominal muscle expiratory activity, we performed transient testing of peripheral chemoreceptor function (pure O2 and N2 inhalation, KCN injection). To assess the influence of central chemoreceptor afferents, we compared results obtained during hypocapnic and isocapnic 15-min hypoxic runs (fractional concentration of inspired O2 0.08) in each lamb. We also compared results obtained in intact and vagotomized lambs so that the importance of vagal afferents could be assessed. We consistently observed abdominal muscle expiratory EMG activity in each lamb, whether intact or vagotomized, during baseline room air breathing; further recruitment was observed during hypoxia. We also consistently observed abdominal muscle expiratory recruitment during hypocapnic hypoxia in each lamb, although it was significantly less marked than during isocapnic hypoxia. Our transient testing of peripheral chemoreceptor function showed, furthermore, that peripheral chemoreceptor afferents dynamically modulate abdominal muscle expiratory activity. Thus, during hypoxia in 11- to 22-day-old awake nonsedated lambs, increased afferent information from peripheral chemoreceptors forcefully enhances abdominal muscle expiratory activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of Chemoreceptors on Neurohypophyseal Blood Flow During Hypoxic Hypoxia

Influence of Chemoreceptors on Neurohypophyseal Blood Flow During Hypoxic Hypoxia

Influence of chemoreceptors on neurohypophyseal blood flow during hypoxic hypoxia.

Neurohypophyseal blood flow was studied using radiolabelled microspheres in 13 dogs. Hypoxic hypoxia and carbon monoxide hypoxia with similar arterial oxygen contents (CaO2, approximately 8 vol %) were produced. Under conditions of hypoxic hypoxia, 100-200% increases in blood flow in caudate nucleus, white matter, neurohypophysis, and all other brain regions occurred. Similar blood flow responses were observed with carbon monoxide hypoxia in all brain regions except the neurohypophysis. The role of carotid and aortic chemoreceptors in mediating this blood flow response was studied in 6 additional dogs. Similar degrees of hypoxic hypoxia were produced in chemoreceptor-intact and completely denervated animals (CaO2 approximately 8 vol %, PaO2 approximately 33 mm Hg). Hypoxic hypoxia produced a 250% increase in neurohypophyseal blood flow and a concurrent rise in plasma arginine vasopressin from 8 +/- 3 to 52 +/- 8 pg/ml. Chemoreceptor denervation completely inhibited the increase in neurohypophyseal blood flow associated with hypoxic hypoxia. Arginine vasopressin was not increased by hypoxic hypoxia under conditions of complete denervation. A unique role for peripheral chemoreceptors in regulating neurohypophyseal blood flow is postulated.

Comparison of respiratory-related trigeminal, hypoglossal and phrenic activities

In decerebrate, paralyzed and vagotomized cats, we recorded activities of hypoglossal and phrenic nerves and of the mylohyoid branch of the trigeminal nerve. At normocapnia, a respiratory-modulated trigeminal discharge could be discrened in most cats. This discharge was characterized by a diminution of activity during neural inspiration and a peak in expiration. In hypercapnia or hypoxia, peak activity increased and its time of occurence moved to late inspiration. Augmentations of peak trigeminal, hypoglossal and phrenic activities were proportional. Peak trigeminal and hypoglossal activities increased more than phrenic following administration of protriptyline, strychnine and, in some cats, cyanide or doxapram. Peak trigeminal activity fell more than phrenic after diazepam. Pentobarbital or halothane reduced peak hypoglossal, but not trigeminal, activity more than phrenic. However, after these anesthetics, trigeminal activity became restricted to the inspiratory-expiratory junction. We conclude that trigeminal and hypoglossal activities are more dependent upon processes within the retcicular formation than in the bulbospinal-phrenic system. Central and peripheral chemoreceptor influences are distributed equivalently upon trigeminal, hypoglossal and phrenic motoneurons.

1696 EFFECTS OF UPPER AIRWAY (UA) INTRALUMINAL PRESSURE ON RESPIRATORY FREQUENCY

Reduced respiratory frequency (f) is seen during obstructive and mixed apnea. Since intrathoracic pressure changes in obstructive and mixed apnea are conducted to the larynx and pharynx, we wondered if UA pressure changes could contribute to the reduced f, in addition to lung and chemoreceptor reflexes. Therefore, we studied the effects of UA pressure changes on f by raising or lowering the pressure in the isolated UA (nose, pharynx and larynx) during tracheostomy breathing and by adding respiratory loads (airway occlusion) after eliminating lung stretch reflexes by cervical vagotomy. Comparison of the first occluded with the preceding breath eliminated chemoreceptor influences. The integrated diaphragmatic EMG was used to determine f. The effect of a sustained pressure change in the isolated UA was tested in 15 anesthetized (Pentothol) rabbits. A rapid decrease in f during negative pressure change (up to 35%) and an increase in f during positive pressure change (up to 20%) were seen. The percentage change in f correlated with the magnitude of pressure change (2-10cm H2O). The nasal or tracheostomy airway was occluded briefly (at FRC) in 6 vagotomized animals. During nasal occlusion inspiratory and respiratory cycle duration was prolonged (10-20%) whereas no change was seen during tracheostomy occlusion. We conclude that response to UA pressure changes may contribute to the reduced respiratory frequency seen during mixed and obstructive apnea. (Funding: NIH grant#HD10993)

Arterial and cardiopulmonary baroreceptor and chemoreceptor influences and interactions on ear sympathetic nerve discharge in the rabbit.

1. The effects of changing intravascular pressures on integrated ear sympathetic nerve activity (ESNA) were studied in anesthetized artificially ventilated rabbits by inflating aortic and inferior vena caval perivascular balloons under conditions of normal arterial Po2 and during arterial hypoxia. 2. At normal Po2 ESNA was unaffected by arterial and cardiopulmonary baroreflex influences. The small inhibition of ESNA observed during rises in arterial pressure after vagotomy was also present after section of the carotid sinus and aortic nerves, and after cutting both vagi as well. 3. During hypoxia there was marked inhibition of ESNA, which was minimally influenced by vagotomy but abolished by section of the carotid sinus and aortic nerves, suggesting that it was chemoreceptor-mediated. There was a pressure-related rise in ESNA which was abolished by vagotomy and considered to be due to a central nervous chemoreceptor-cardiopulmonary baroreflex interaction.

Central Nervous System and Chemoreceptor Factors in Control of Breathing

The respiratory control system at a conceptual level includes a set of receptors, some of which are chemoreceptors, which gather information about their environment and a complex array of neural connections which processes and sends the information to a set of effectors, the muscles, which produce ventilation. Although in the past most attention has been paid by respiratory physiologists to the chemoreceptor influences, it should be apparent that the neural elements of the system are crucial to its understanding.

Baroreceptor and chemoreceptor influences on sympathetic discharge to the heart

Baroreceptor and chemoreceptor influences in the regulation of sympathetic discharge to the heart were investigated, utilizing electroneurographic recordings from the left inferior cardiac nerve in the cat. Spontaneous discharge patterns exhibited phasic inhibition with the heartbeat and with inflation of the lungs. This was shown to be the consequence of baroreceptor and afferent vagal activity, respectively. Increasing blood pressure with epinephrine or angiotensin II caused marked inhibition of discharge which was abolished by baroreceptor deafferentation. No increase of cardiac sympathetic discharge occurred after the introduction of hypoxic blood into the isolated carotid sinus. Systemic hypoxia caused a marked increase in sympathetic discharge to the heart despite a large increase of systemic blood pressure. This response persisted after denervation of the peripheral chemoreceptors. A similar but less pronounced response to systemic hypercapnia was found. Systemic hypoxia frequently produced bradycardia which could be converted to tachycardia by atropine. This was associated with a large and continuous increase of cardiac sympathetic discharge to the heart. It is concluded that in systemic hypoxia both sympathetic and parasympathetic discharge to the heart is enhanced.

Carotid and vagal afferents and drug action on transcallosally evoked cortical potentials.

The use of transcallosally evoked cortical potentials to study the action of intracarotidly injected drugs on cerebral synapses has necessitated the demonstration that vagal, baroreceptor, and chemoreceptor influences do not play essential roles in the drug effects observed-for example, the cerebral synaptic inhibitory action of serotonin.

Carotid and Vagal Afferents and Drug Action on Transcallosally Evoked Cortical Potentials

The use of transcallosally evoked cortical potentials to study the action of intracarotidly injected drugs on cerebral synapses has necessitated the demonstration that vagal, baroreceptor, and chemoreceptor influences do not play essential roles in the drug effects observed—for example, the cerebral synaptic inhibitory action of serotonin.