Objectives This study sought to determine the most effective technique for Valsalva Manoeuvre (VM) and Human Dive Reflex Manoeuvre (HDR) generation of vagal tone.

Methods We conducted a repeated-measures trial of healthy adult volunteers from a university campus, aged 18–56 years, in sinus rhythm. Participants were randomised to VM (in supine or Trendelenberg postures) and HDR (supine or sitting postures) sequentially. Participants performed three trials of each technique, in random order, with a continuous ECG recording. Single-blinded analysis of ECG data was conducted. Mean differences between premanoeuvre and postmanoeuvre R-R intervals and heart rates were calculated for each posture within and between vagal manoeuvres.

Results Seventy-two participants were enrolled. The difference between VM (supine) and VM (Trendelenberg) was not significant at 0.008 s (−0.023 to 0.038). The difference in mean R-R intervals for HDR (supine) was greater than HDR (sitting) 0.062 (0.031 to 0.093), although this significance was not reflected in a heart-rate change of −0.87 (−3.00 to 1.26). VM supine generated greatest overall mean R-R interval difference, while HDR (sitting) provided the smallest change in R-R interval. The VM (supine) provided a significant maximum effectiveness over the HDR (supine) of 0.102 s (0.071 to 0.132).

Conclusions This study demonstrates that VM (supine) generates the greatest vagal tone producing the largest transient heart rate decrease in healthy volunteers. No advantage was identified in Trendelenberg posturing for the VM in this study. These results may assist in the standardisation of vagal manoeuvre technique for the range of therapeutic and diagnostic applications.