Effects of metronome breathing on the assessment of autonomic control using heart rate variability

Analysis of Heart Rate Variability is a non-invasive quantitative tool to study the influence of the autonomic nervous system on the heart. Rapid variations in heart rate, related to breathing are primarily mediated by the vagal limb of the autonomic nervous system. The resulting variations in heart rate are usually referred to as respiratory sinus arrhythmia. Metronome breathing (MB) is often advocated to assess more accurately vagal control. However, the additional value of MB over SB has never been established. The authors studied the effect of MB (0.25 Hz) on HRV variables in 12 healthy male subjects under stable conditions using pharmacological autonomic blockade. During MB several variables showed a lower absolute value, however a strong correlation existed between variables computed during spontaneous breathing (SB) and MB. MB offers some, but no important advantages over spontaneous breathing.