Effects of midazolam on respiratory muscles in humans.

Midazolam at sedative doses alters the breathing pattern; however, its effects on respiratory load and respiratory muscle activity have not been established completely. Therefore, the effects of midazolam (0.1 mg/kg) on total pulmonary resistances and on diaphragmatic, intercostal, and abdominal muscle patterns were studied in nine volunteers. Measurements were performed during control, 5 and 10 min after midazolam, and then 2 min after 1.0 mg of intravenous flumazenil. After midazolam, total pulmonary resistance increased from 6.3 +/- 0.65 to 36.6 +/- 8.1 cm H2O-L-1 x s-1 (P < 0.01), a pattern associated with an increased intercostal electromyographic activity (peak and slope; P < 0.05). By contrast, the ratio of gastric pressure on esophageal pressure changes decreased from 65.5% +/- 6.2% to 16.3% +/- 3.9% (P < 0.01), indicating reduced diaphragmatic activity. In 7/9 subjects, there was expiratory abdominal muscle activity. Flumazenil reversed all these effects. We conclude that midazolam 0.1 mg/kg increases total pulmonary resistance and elicits a compensatory load response characterized by an increase in inspiratory intercostal and expiratory abdominal muscle activities whereas diaphragmatic contribution is reduced.