A vagally mediated response to metabolic acidosis in anesthetized rabbits.

Pentobarbital sodium-anesthetized rabbits received 10-min infusions of acetic, lactic, or propionic acid delivered via a catheter to the right atrium at a rate of 1 mmol/min (n = 14). Arterial [H+] increased by 35.8 +/- 7.

Chemoreflexes in rabbits.

Criteria defining chemoreflexes (called responses) in rabbits have been established in relation to right atrial injection of 16 chemicals, and compared with previously-defined chemoreflexes of cats. A vagally mediated 'pulmonary' response elicited at latencies less than 1.6 sec consists only of an increased frequency of breathing due primarily to decrease of expiratory duration.

CO2/H+ receptors in the lungs of anaesthetized rabbits.

The CO2/H+ sensitivity of 'pulmonary' non-myelinated vagal afferent endings was investigated in anaesthetized rabbits using 'natural' stimuli of lactic (LA) and acetic (AA) acids, for comparison with previous results using sodium dithionite (NaD) and phenyl biguanide (PDG). Right atrial injections of these four chemicals demonstrated a respiratory reflex from 'pulmonary' endings, consisting primarily of a decrease in expiratory duration and consequent increase in respiratory frequency coincident with transient increase in PETCO2. Three of the chemicals (AA, LA and NaD) apparently activated the endings by increased [CO2] and/or [H+], since equimolar doses of sodium lactate and acetate were without effect.

Role of vagal C-fiber afferents in respiratory response to hypercapnia.

The respiratory response to hypercapnia has been investigated in 10 anesthetized rabbits by use of a rebreathing technique. The responses were obtained in three situations: with one intact vagus nerve (control), during differential block of conduction, and after vagotomy. Differential block was achieved using anodal hyperpolarization by application of a direct current to the cervical vagus nerve.

Non-myelinated vagal lung receptors and their reflex effects on respiration in rabbits.

The response characteristics of non-myelinated vagal lung receptors have been studied in the anaesthetized rabbit. The results indicate that the behaviour of these endings strongly resembles those found in cats and dogs and that they can be classified into 'pulmonary' 'bronchial' and 'pulmonary-bronchial' groups depending on their accessibility from either circulation. Experiments involving pericardial block with local anaesthetic to exclude responses from cardiac receptors and the use of sodium dithionite as a novel stimulus to 'pulmonary' endings alone, have shown that the predominant effect of these endings in the anaesthetized rabbit is to increase respiratory frequency.

Do axon reflexes exist within the lung?

Circumstantial evidence is given in support of the hypothesis that vagal lung receptors are involved in local axon reflexes. All the components of such mechanisms are present, and teleologically it would make sense for them to exist. It is suggested that rapidly-adapting or irritant receptors produce local muscle relaxation as well as the centrally-mediated reflex bronchoconstriction in other parts of the lung.

The non-adrenergic, vagal efferent system to the lung: does it exist, or is an artefact?

A third efferent pathway to the lungs - the non-adrenergic vagal inhibitory system - has previously been invoked to explain the residual neurally-mediated bronchodilatation, that is obtained after the administration of cholinergic and adrenergic blocking drugs. However, the experimental results cited as evidence for the existence of this third efferent pathway, can also be explained by an alternative mechanism, involving local axon reflexes in afferent fibres from lung receptors. If this latter explanation is correct, then the existence of the third efferent pathway is an artefact resulting from the experimental conditions.

Role of pulmonary stretch receptors during breathing in rabbits, cats and dogs.

In order to mimic and then modify the input to the respiratory centre from pulmonary stretch receptors, the central ends of the cut cervical vagus nerves were electrically stimulated with a frequency determined by transpulmonary pressure through a voltage to frequency converter. At appropriate end-expiratory stimulation frequency and gain of the voltage to frequency converter, such stimulation restored the pre-vagotomised patterns of breathing in rabbits, cats and dogs. Mimicking the changes in activity from pulmonary stretch receptors that would be produced by such manoeuvres as hypercapnia, inflations and deflations, reproduced the responses in inspiratory duration that occurred with natural stimuli in the same animals with intact.

The direct effect on pulmonary stretch receptor discharge produced by changing lung carbon dioxide concentration in dogs on cardiopulmonary bypass and its action on breathing.

1. Single fibre pulmonary stretch receptor discharge was recorded in dogs on cardiopulmonary bypass. 2.

The effect of carbon dioxide in the airways and alveoli on ventilation; a vagal reflex studied in the dog.

1. The inhalation of CO(2) produces a tachypnoea only in the presence of intact vagus nerves; the present study was designed to examine the mechanism of this phenomenon in the dog.2.

Studies of the pulmonary vagal control of central respiratory rhythm in the absence of breathing movements.

1. Breuer's hypothesis that the vagus nerves exert a tonic control of respiratory rhythm, in addition to the phasic control, was examined.2.

Assessment of differential block of conduction by direct current applied to the cervical vagus nerve.

As investigation has been made of the adequacy of direct current to block conduction in the myelinated fibres of the cervical vagus nerve, leaving the nonmyelinated fibres conducting normally. Conduction was assessed from the compound electroneurograms, and from single fibre recording. Conduction of spontaneous activity and the responses to inflation and deflation in single fibres from lung irritant receptors and pulmonary stretch receptors were completely abolished when the A-B wave of the electroneurogram was absent but the C wave was intact.