Effect of intramedullary procaine injection on tracheal tone and phrenic neurogram

Tracheal tone and the role of ionotropic glutamate receptors in the nucleus ambiguus

Excitatory amino acid (EAA) transmission in the rostral portion of the ventrolateral medulla (RVLM) appears to be required for reflex airway constriction. The purpose of the present study was to determine whether our prior observations of right sided dominance are also reflected at the level of the RVLM, particularly at the right nucleus ambiguus (NA). Microinjection of glutamate (109 nl, 100 mM) into the right NA of anesthetized dogs produced significant increases in tracheal smooth muscle tone as assessed by pressure changes in a saline filled cuff of the endotracheal tube (Delta15 +/- 2 mm Hg). Increasing inspired CO2 increased tracheal cuff pressure (Delta33 +/- 2 mm Hg) which was abolished by microinjections of the EAA antagonist kynurenic acid (109 nl, 100 mM) or the non-NMDA antagonist 6-nitro-7-sulfamobenzoquinoxaline-2,3-dione (NBQX, 109 nl, 10 mM) into the right NA. These results confirm that EAA receptors in the right NA are capable of modulating tracheal tone and suggest that non-NMDA receptors in the right NA are required for reflex airway constriction produced by systemic hypercapnia. Furthermore, the effects of right-sided NA microinjections in the present study, although not completely definitive, are consistent with previous studies that suggest dominant control of canine tracheal tone by the right vagus.

New strategies of screening and treatment for sleep apnea syndrome

The prevalence of sleep apnea syndrome (SAS) is approximately 7.5% in Japanese adults aged 18-68 years old. SAS is characterized by repeated episodes of apnea, especially obstructive apnea, during sleep. Severe SAS has life-threatening complications such as pulmonary hypertension, arrhythmias, right heart failure or brain damage, which could be caused by hypoxemia and/or hypercapnia. Upper airway relaxation is responsible for the obstruction during apnea, and an increase in the activities of the upper airway muscles dilates and stiffens the upper airway wall. Maintaining the activities of the upper airway muscles may contribute to keeping the airway patent. Submental electrical stimulation of the upper airway muscles would be a novel treatment method for obstructive apnea.