FIGURE 1.

Influence of TRH or placebo (normal saline) on remifentanil‐induced respiratory depression at iso‐hypercapnia in human volunteers. Initially, the end‐tidal PCO₂ was elevated so that minute ventilation increased to 20 ± 5 L/min. After reaching steady‐state ventilation, remifentanil was titrated to cause a depression of ventilation of 50%. Subsequently TRH (panels A‐F) or placebo (panels G‐I) were administered as a bolus dose followed by a continuous infusion over 30 min. In all but one subject (Panel F), this dosing sequence was repeated once. The data are obtained from seven healthy volunteers of either gender. Data from panels A and G and B and H are from the same subjects. Each symbol represents the minute ventilation averaged over 1‐min. The red dotted line gives the average ventilation prior to TRH or placebo administration.