ACUTE EFFECT OF LORAZEPAM ON RESPIRATORY MUSCLES IN PATIENTS WITH CHRONIC OBSTRUCTIVE PULMONARY-DISEASE

Benzodiazepines are known to cause muscle hypotonia, but their effects on respiratory muscle function, particularly on diaphragm, have not y et been studied. Our aim was to look for any effect of lorazepam on re spiratory muscle function in patients with chronic obstructive pulmona ry disease (COPD). Nine stable COPD patients (mean +/- SD forced expir atory Volume in one second (FEV(1)) 0.91 +/- 0.31 I) were included in the study. The following measurements were performed before and 1 hour after lorazepam administration (doses: 1.5 to 2 mg) by sublingual rou te: forced vital capacity (FVC), FEV(1), maximal voluntary ventilation (MVV), arterial oxygen tension (PaO2), arterial carbon dioxide tensio n (PaCO2), minute ventilation (Ve), tidal volume (Vt), respiratory rat e (f), inspiratory time/inspiratory plus expiratory time (Ti/Ttot), me an inspiratory flow (Vi), maximal inspiratory (MIP) and expiratory (ME P) pressures, maximal pleural pressure (PpI(max)), transdiaphragmatic pres sures (Pdi) and skeletal muscle strength and endurance. As expect ed, no change was noted in FVC, FEV(1), FEV(1)/FVC (Table 1). Besides stability of expiratory flows, this denotes no change in collaboration in spite of the sedative effects of lorazepam. There was a 20% decrea se in Ve, due to a Vt reduction and a small increase in PaCO2. These c ould be explained by the central effects of benzodiazepines. Skeletal muscle strength and endurance decreased significantly (22 and 50% resp ectively - Table 2), in accordance with the previously reported muscul ar actions of this pharmacological group. Respiratory muscle function parameters, MIP, MEP, MVV and PpI showed significant reductions (10 to 20 per cent), as was the case with diaphragmatic function measured by Pdi (Muller maneuver with abdominal protrussion and maximal open-glot tis expulsive maneuver) (Table 3). This study demonstrates that a sing le lorazepam dose reduces strength and endurance of respiratory muscle in chronic stable COPD patients.