1. Sedatives such as the benzodiazepines and alcohol reduce upper airway muscle activity. We hypothesized that a sedating antihypertensive, α-methyldopa, might have similar effects. To investigate this hypothesis we studied the effect of α-methyldopa on alae nasi electromyographic (EMG) activity during hypercapnia.

2. We studied ten healthy subjects and three subjects with obstructive sleep apnoea during CO2-stimulated breathing. In a preliminary study four subjects demonstrated a fall in alae nasi EMG activity 4 h after the ingestion of 500 mg of α-methyldopa during CO2 rebreathing.

3. In six additional normal subjects and three subjects with obstructive sleep apnoea, we studied the alae nasi EMG activity during steady-state hypercapnia with PCO2 held constant 5 torr (0.7 kPa) above baseline. On 2 separate days we studied subjects before and 2 h after they had ingested 750 mg of α-methyldopa or placebo.

4. In the normal subjects the mean alae nasi EMG activity fell by 34% 2 h after ingestion of α-methyldopa (P < 0.05) without a change in other ventilatory parameters.

5. In the sleep apnoea group the individual mean alae nasi EMG activity fell 16–49%, with ventilation and tidal volume falling in one patient.

6. We conclude that α-methyldopa selectively reduces upper airway motor activity.

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