Leg elevation compared with Trendelenburg position: effects on autonomic cardiac control.

We have studied in 12 healthy male volunteers the effects of three different body positions (10 degrees head-down tilt, horizontal supine and supine with 50-cm leg elevation from the hip) on the spectral components of heart rate and finger plethysmographic amplitude variability. We have demonstrated the absence of any statistically significant difference in any measure of variability in the time of frequency domain for both of these measures between the three positions. We conclude that neither leg elevation nor 10 degrees head-down tilt is associated with any significant alteration in the dominant parasympathetic cardiac control in comparison with the resting supine position.