Fig. 3. Effect of tilt-table testing on the mean of all normal RR intervals (mean RR interval), cardiac output, and total peripheral resistance in patients (squares ) and control subjects (circles ). Hemodynamic parameters were measured during 10 min supine rest (Baseline), two times 10 min in 60^oupright position (Upright 1, Upright 2), and 10 min supine recovery (Recovery). For the mean RR interval (A ) the main effect of the group was significant with significantly decreased RR interval in patients compared with control subjects during all four conditions. For cardiac output and total peripheral resistance there was a significant condition by group interaction. Patients had a significantly higher reduction in cardiac output (B ) and increase in total peripheral resistance (C ) compared with control subjects, at the change from supine baseline to upright position. These changes remained significant during the recovery period. Asterisks  indicate significant changes. Values in mean (SD). ms = milliseconds; RR interval = mean time between consecutive normal R waves in the QRS complexes.