Effect of graded head-up tilt on parasympathetic reactivity.

Thirteen healthy subjects were tested for parasympathetic reactivity during head-up tilt and reversal of the tilt. Head-up tilt (70 degrees) resulted in significant increase in baseline heart rate and diastolic blood pressure. Head-up tilt also led to increased parasympathetic reactivity as measured by Valsalva manoeuvre and hand grip test. Heart rate response to deep breathing test did not change. The reversal of the tilt led to returning of heart responses to original values. Responses indicate towards enhanced parasympathetic reactivity during head-up tilt position.