Stránsky A

The effects of lung reflexes on laryngeal resistance and motoneurone discharge

1. The reflex action of stimulation of alveolar J–receptors and of airway epithelial irritant receptors has been investigated on laryngeal resistance to airflow and on laryngeal motoneurone discharge in cats and rabbits.

Short reflex expirations (expiration reflexes) induced by mechanical stimulation of the trachea in anesthetized cats.

Fifty spontaneously breathing pentobarbital-anesthetized cats were used to determine the incidence rate and parameters of short reflex expirations induced by mechanical stimulation of the tracheal mucosa (ERt). The mechanical stimuli evoked coughs; in addition, 67.6% of the stimulation trials began with ERt. The expiration reflex mechanically induced from the glottis (ERg) was also analyzed (99.5% incidence, p < 0.001 compared to the incidence of ERt). We found that the amplitudes of abdominal, laryngeal abductor posterior cricoarytenoid, and laryngeal adductor thyroarytenoid electromyograms (EMG) were significantly enhanced in ERg relative to ERt. Peak intrathoracic pressure (esophageal or intra-pleural pressure) was higher during ERg than ERt. The interval between the peak in EMG activity of the posterior cricoarytenoid muscle and that of the EMG of abdominal muscles was lower in ERt compared to ERg. The duration of thyroarytenoid EMG activity associated with ERt was shorter than that in ERg. All other temporal features of the pattern of abdominal, posterior cricoarytenoid, and thyroarytenoid muscles EMGs were equivalent in ERt and ERg.In an additional 8 cats, the effect of codeine administered via the vertebral artery was tested. Codeine, in a dose (0.03 mg/kg) that markedly suppressed cough did not significantly alter either the incidence rate or magnitudes of ERt.In the anesthetized cat the ERt induced by mechanical stimulation of the trachea was similar to the ERg from the glottis. These two reflex responses differ substantially only in the frequency of occurrence in response to mechanical stimulus and in the intensity of motor output.

Reflex control of discharge in motor fibres to the larynx

1. Action potentials have been recorded from single laryngeal motor fibres, with expiratory or inspiratory phases, in cats anaesthetized with pentobarbitone and breathing through a tracheal cannula.

Characteristics of augmented breaths provoked by almitrine bismesylate in cats

The contribution of almitrine bismesylate to the occurrence and pattern of augmented breaths was studied in fifteen spontaneously breathing, anaesthetized cats. Breathing was via a tracheostomy, while the laryngeal resistance to airflow was measured with the larynx isolated in situ. Almitrine bismesylate at a dose of 0.5 mg kg‐1 of body weight was injected intravenously in the intact animals and following bilateral vagotomy which spared the right recurrent laryngeal nerve. Almitrine injected intravenously elicited augmented breaths within the first 45 s in thirteen cats and within 1 min in the remaining two cats. During augmented breaths inspiratory and expiratory airflows rose, the mean increases being 385.2 and 159.6% respectively above the controls (P less than 0.01). The inspiratory laryngeal resistance declined to 77.7% of the control (P less than 0.01) and expiratory laryngeal resistance increased by 95.4% above the control level (P less than 0.01). The inspiratory and expiratory times were prolonged by 56 and 58% compared with baseline breathing. Following the augmented breaths the respiratory airflows exceeded baseline values, the respiratory timing was slightly reduced, and the inspiratory laryngeal resistance was significantly lowered below the control level (P less than 0.01). The expiratory laryngeal resistance showed the same trend without statistical significance. Bilateral vagotomy abolished the occurrence of augmented breaths following almitrine injection.

Action of Almitrine on the Laryngeal Passage in Cats

There have been a number of animal and human studies regarding the effects of almitrine bismesylate on ventilatory parameters. The size of respiratory changes depends on the preserved integrity of the carotid sinus and vagal nerves (Laubie and Diot, 1972; Laubie and Schmitt, 1980; Dhillon and Barer, 1982; De Backer et al., 1985), which befits with the pattern of the hypoxic response. The latter is known to elicit the expiratory vocal cord abduction, i.e. the decline in the resistance to flow posed by the larynx. Furthermore, the ammeliorating effect of almitrine bismesylate in patients with OSAS (Krieger et al., 1982) suggests that the upper airway airflow resistance might lower. No studies are yet available devoted to the evaluation of this problem. We have investigated the laryngeal response to almitrine bismesylate in cats, trying to assess the contribution of the vagal and sensory laryngeal inputs.

THE PATHOPHYSIOLOGICAL ROLE OF THE SNIFF-LIKE ASPIRATION REFLEX

Publisher Summary This chapter discusses the pathophysiological role of the sniff-like aspiration reflex (AR). Nasopharyngeal stimulation can evoke a sniff-like AR in cats, dogs, rats and some other mammals. It is characterized by marked respiratory, cardiovascular, somatomotor, and bronchomotor changes. AR may have the same underlying mechanisms as the accelerator respiratory reflex elicited by stimulation of the palatopharyngeal mucosa or the corresponding afferent nerves. The chapter reviews the most important effects of the sniff-like AR with possible experimental and clinical applications. It also discusses the main components and some characteristics of the reflex. The chapter describes the mechanical and humorally-mediated effects of the AR and their possible applications in some physiological and pathological conditions. The nasopharyngeal stimulation and the AR proved to be an effective method of resuscitation from clinical death and a promising approach for inhibition of some pathological respiratory acts.

Pattern of breathing and laryngeal patency following almitrine bismesylate in anesthetized cats

SummaryThe effects of almitrine bismesylate on the pattern of breathing and laryngeal caliber were investigated in anesthetized, spontaneously breathing cats. Breathing occurred via a tracheostomy, while the laryngeal resistance to airflow was measured with the larynx isolated in situ. Almitrine bismesylate in a dose of 0.5 mg/kg of body weight was injected intravenously three times: in the intact animals, following bilateral vagotomy (sparing the right recurrent laryngeal nerve), and after a sensory denervation of the larynx. In each condition, almitrine stimulated ventilation by significantly increasing inspiratory airflow, by increasing the respiratory rate in the 10th and the 20th minutes following injection, and by reducing laryngeal resistance to airflow in both the inspiratory and expiratory phases. The stimulatory effects of almitrine were most apparent in the intact animals. Following vagotomy, these significant changes in the pattern of breathing as well as the enlarged laryngeal caliber persisted. However, these latter effects were short-lived and were followed by narrowing of the laryngeal lumen. Laryngeal afferents were not essential for the response to almitrine.