Low-dose mirtazapine increases genioglossus activity in the anesthetized rat.

STUDY OBJECTIVES: To examine the effects of mirtazapine on genioglossus and diaphragmatic electromyogram activity in the anesthetized rat. DESIGN: Parallel-group study. SUBJECTS: Sprague-Dawley adult male rats, 10 in each of 3 groups were studied. INTERVENTIONS: After anesthesia with 1.2 g/kg of urethane, a tracheostomy and bilateral vagotomy were performed. Femoral arterial and venous lines were placed, and fine wire hook electrodes were implanted into the genioglossus and diaphragm muscles. MEASUREMENTS: After a baseline period of measurement, either saline, 0.5 mg/kg of mirtazapine, or 5.0 mg/kg of mirtazapine was injected via the intraperitoneal route, and measurements were made for the next 3 hours. The average peak and tonic values of the moving time average of the genioglossus and diaphragm electromyogram for hours 1, 2, and 3 were determined and expressed as a percentage of the corresponding average value during the baseline (preinjection) monitoring period. RESULTS: At 0.5 mg/kg of mirtazapine, the peak genioglossus electromyogram was significantly higher than in control conditions over hours 2 and 3. At 5.0 mg/kg of mirtazapine, the genioglossus electromyogram was significantly lower than in control conditions for the first 2 hours of monitoring. The peak diaphragmatic electromyogram was slightly but significantly lower in the mirtazapine 5.0-mg/kg group than in controls. CONCLUSIONS: Mirtazapine, at a dose similar to one used clinically, increased genioglossus activity. We hypothesize that, at this dose, the ability of mirtazapine to increase serotonin and norepinephrine or block type-3 serotonin receptors predominated. At the higher dose of mirtazapine, the type-2 blockade effect predominated and genioglossus activity decreased.

Comparison of respiratory event detection by a polyvinylidene fluoride film airflow sensor and a pneumotachograph in sleep apnea patients.

STUDY OBJECTIVES: Compare the ability of a polyvinylidene fluoride (PVDF) thermal sensor and a pneumotachograph to detect respiratory events in patients with obstructive sleep apnea. DESIGN: Single night of monitoring, single blinded scorer. SETTING: Veterans Affairs medical center. PATIENTS: Ten male subjects with obstructive sleep apnea. INTERVENTIONS: Nasal-oral airflow was simultaneously detected by a PVDF thermal sensor attached to the upper lip and a pneumotachograph in a mask over the nose and mouth. MEASUREMENTS: Events were scored from display views showing only the airflow tracings of the sensor in question and the events scored from that sensor. The apnea-hypopnea index was computed using two definitions for hypopnea. Hypopnea-1 was defined as a 50% reduction in flow for > or = 10 s in duration. Hypopnea-2 was defined as any reduction in airflow for > or = 10 s associated with a 3% drop in the arterial oxygen saturation or followed by an arousal. The level of agreement (kappa) for the sensors was determined by comparing whether or not they identified candidate events determined by a second blinded scorer. RESULTS: For the apnea-hypopnea-1 index (mean +/- SD), the event rate for the pneumotachograph (26.0 +/- 27.9 events/h) was slightly greater than that for the PVDF sensor (20.1 +/- 27.1 events/h; p < 0.05). For the apnea-hypopnea-2 index, the event rate for the pneumotachograph (29.4 +/- 26.8 events/h) and for that of the PVDF sensor (26.4 +/- 25.9 events/h) were similar (difference not significant). The mean +/- 2 SD difference was 3.0 +/- 8.5 events/h. The level of agreement between the sensors was in the "good range," whereby kappa = 0.69. For 20 randomly selected breaths per patient, the maximum deflections of the PVDF sensor varied linearly with pneumotachograph airflow deflections. CONCLUSION: The PVDF sensor compared favorably with a "gold standard" method of detecting respiratory events during sleep in patients with obstructive sleep apnea.