RESUMEN
Reduced vagally mediated heart rate variability (VmHRV) has been reported in patients with chronic pain. In healthy persons, breathing with longer expiration relative to inspiration increases VmHRV at 12 breaths per minute. The present study aimed to determine the immediate effect of breathing with longer expiration relative to inspiration on VmHRV and mood states in patients with chronic pain. Fifty patients with chronic pain aged between 20 and 67 years were prospectively randomized as two groups with an allocation ratio of 1:1. The interventional group practiced breathing with metronome based visual cues, maintaining an inspiration to expiration ratio of 28:72 (i/e ratio, 0.38) at a breath rate of 12 breaths per minute. The average i/e ratio they attained based on strain gauge respiration recording was 0.685 (SD 0.48). The control group, which looked at the metronome without conscious breath modification had an average i/e ratio of 0.745 (SD 0.69). The VmHRV, respiration and self-reported mood states (using the Brief Mood Introspection Scale (BMIS)) were assessed. There was a significant increase in HF-HRV and RMSSD during low i/e breathing (repeated measures ANCOVA, Bonferroni adjusted post-hoc test, p < 0.05; in all cases). Self-reported mood states changed as follows: (i) following low i/e breathing positive-mood states increased while the aroused mood state decreased whereas (ii) following the control intervention the aroused mood state increased (repeated measure ANOVA, p < 0.05; in all cases). Hence breathing with prolonged expiration is possibly useful to increase VmHRV and improve self- reported mood states in patients with chronic pain.