Table 2. ED50(95% Confidence Intervals) Values for Infusion of Propofol (mg · kg−1· min−1) and Remifentanil (μg · kg−1· min−1), Alone and in Combination, on Phrenic Nerve Activity (PNA), and Changes in HR and MAP (ΔHR and ΔMAP) Evoked by 5-s Trains of Supramaximal High Frequency Electrical Stimulation (30 Hz, 30V, duration 0.5 ms) of Tibial Nerves, and the Ratios of the ED50s for ΔHR and ΔMAP to PNA