Effect of Bedtime Ethanol on Total Inspiratory Resistance and Respiratory Drive in Normal Nonsnoring Men

We have previously reported that bedtime ethanol (2.0 ml/kg of 100 proof vodka) increases upper airway closing pressure in males who habitually snored but were otherwise healthy. We also observed that some of these snorers developed obstructive apneas. To explore this phenomenon in more detail, we measured the inspiratory resistance (R_I) and respiratory drive after bedtime ethanol in 10 nonobese men (ages 23 to 33) with no history of snoring. Subjects went to bed wearing a tightly fitting valved mask over the nose and mouth that allowed measurement of inspiratory and expiratory flow, pressure in the mask, and endtidal CO₂. We measured R_I by calculating the pressure difference between the mouth and a balloon positioned in the midesophagus. Respiratory drive was quantified by the inspiratory occlusion pressure (P_0.1), the ventilatory response to hyperoxic hypercapnia (ΔV_E/ΔP_ETCO₂), and the ventilatory response to isocapnic hypoxia (ΔV_E/ΔS,O₂). Measurements were made during waking and during stage 2 NREM sleep on two nights: (1) when the subjects drank 1.5 ml/kg of 100 proof vodka in orange juice over a 30-min period 15–45 min before lights out and (2) when the orange juice contained less than 0.1 ml of vodka floating on the top. Eight of the nine men in whom we had technically adequate measurements showed a rise in R_I during NREM sleep above the waking level on both control and ethanol nights and the sleeping R_I was greater on the ethanol than on the control night. There was a tendency for P_0.1 to be higher during sleep and greater on the ethanol night, suggesting that the neural output to the respiratory muscles was not depressed and may have been stimulated by the inspiratory “loading” secondary to the increased R_I. The hypercapnic response was significantly depressed during sleep. Whereas the response tended to be less on the ethanol than on the control night, the difference was not significant. The hypoxic response showed little change from waking to sleeping and no significant change with ethanol. We speculate that inspiratory loading due to increased upper airway resistance tends to stimulate respiratory drive and thereby partially offsets the depressant effect of ethanol on the central respiratory chemoreceptors.