Effects of upper airway carbon dioxide on upper airway resistance and muscle activity in young guinea-pigs

Abstract

The upper airway (UA) of adult animals is known to contain carbon dioxide‐sensitive receptors and UA CO2 reflexly affects breathing, UA dilator muscle activity and UA resistance. These effects may function in the control of UA patency. There is evidence that some UA reflexes are stronger in young than in adult animals, but it is not known whether CO2‐sensitive receptors are present in the UA of young animals, and the effects of UA CO2 on UA resistance and on UA dilator muscle activity have not been investigated in young animals. The responses of ventilation, UA resistance and geniohyoid muscle electromyographic activity to warm air containing 10% CO2 applied to the isolated UA were measured in anaesthetized, vagotomized young guinea‐pigs breathing spontaneously through a low‐cervical tracheostomy. Upper airway carbon dioxide caused an increase in ventilation (46.7±16.3 to 49.9±16.8 mL·min‐1·100 g body weight‐1) and upper airway resistance (56.8±14.8 to 63.7±17.7 cmH2O·L‐1·s‐1·kg body weight‐1). Similar effects were obtained following vagotomy. Geniohyoid activity became apparent following vagotomy and this activity was reduced by upper airway carbon dioxide. These responses were abolished by topical anaesthesia of the upper airway. This suggests that the reflexes seen are due to carbon dioxide‐sensitive receptors in the upper airway.

Elevated body temperature enhances the laryngeal chemoreflex in decerebrate piglets

“…Similarly, the response to upper airway CO 2 is variable among species. Increased CO 2 in the isolated upper airway of young guinea pigs actually stimulated ventilation (8), but increased upper airway CO 2 had no effect on ventilation in adult guinea pigs (A. K. Curran, unpublished observations). Furthermore, upper airway CO 2 had little or no inhibitory effect on geniohyoid or diaphragmatic electromyograph in anesthetized adult rats (33), and no inhibitory effect on ventilation (32).…”

Geniohyoid muscle function in awake canines

“…Several investigators found phasic Genio EMG activity during resting breathing in rats (30), rabbits (4,34), and canines (39), but always under anesthesia. On the other hand, anesthetized young guinea pigs do not have phasic Genio EMG activity (9,10). Van Lunteren et al (41) also demonstrated that Genio was electrically inactive and lengthening during resting breathing, but actively shortening with EMG activity during moderate CO 2 stimulation, in anesthetized cats.…”

Coordinated Respiratory Motor Activity in Nerves Innervating the Upper Airway Muscles in Rats

“…Some reports have demonstrated that the geniohyoid muscles, which are innervated by the HGN, had no phasic respiratory electromyographic activity in anesthetized cats [22] and young guinea pigs [23]. In contrast, other investigators have demonstrated that the geniohyoid and genioglossus muscles, which are also innervated by the HGN, had phasic inspiratory activity during resting breathing in anesthetized rats [24], rabbits [25], and dogs [26].…”