Friday, August 2, 2013

Pain modulation induced by respiration: phase and frequency effects

http://dx.doi.org/10.1016/j.neuroscience.2013.07.048, How to Cite or Link Using DOI

^a Départment de Psychologie, Université de Montréal, Montréal, QC, Canada H3T 1J4
^b Départment de Chiropratique, Université du Québec à Trois-Rivières, Trois-Rivières, QC, Canada G9A 5H7
^c Départment de Stomatologie
^d Centre de recherche en neuropsychologie et cognition (CERNEC)
^e Centre de recherche, Institut universitaire de gériatrie de Montréal (CRIUGM)
^f Université de Montréal, Montréal, QC, Canada H3T 1J4

http://dx.doi.org/10.1016/j.neuroscience.2013.07.048, How to Cite or Link Using DOI

Highlights

•: Manipulation of respiration produced small effects on shock pain and brain activity
•: Hypoalgesic effects involved respiration phase but not frequency
•: Hypoalgesic effects were independent of the inhibition of spinal nociception.
•: Pain inhibition was marginal compared with studies on relaxation techniques
•: The analgesic effects of these techniques may not only depend on respiration.

Abstract

The voluntary control of respiration is used as a common means to regulate pain and emotions and is fundamental to various relaxation and meditation techniques. The aim of the present study was to examine how breathing frequency and phase affect pain perception, spinal nociceptive activity (RIII-reflex) and brain activity (scalp somatosensory evoked-potentials - SEP’s). In 20 healthy volunteers, painful electric shocks individually adjusted to 120% of the RIII-reflex threshold were delivered to the sural nerve near the end of inspiration or expiration phases, during three cued-breathing conditions: 1) Slow breathing (0.1Hz) with slow (4s) inspiration (0.1Hz-SlowIns), 2) Slow breathing (0.1Hz) with fast (2s) inspiration (0.1Hz-FastIns), and 3) Normal breathing (0.2Hz) with fast (2s) inspiration (0.2Hz). Pain ratings were not affected by breathing patterns (p=0.3), but were significantly lower during inspiration compared with expiration (p=0.02). This phase effect was also observed on the N100 component of SEP’s, but only in the 0.1Hz-FastIns condition (p=0.03). In contrast, RIII-reflex amplitude was greater during inspiration compared with expiration (p=0.02). It was also decreased in the 0.1Hz-SlowIns compared with the 0.2Hz condition (p=0.01). Slow breathing also increased the amplitude of respiratory sinus arrhythmia, although these changes were not significantly associated with changes in pain responses. In conclusion, this study shows that pain and pain-related brain activity may be reduced during inspiration but these changes are dissociated from spinal nociceptive transmission. The small amplitude of these effects suggests that factors other than respiration contribute to the analgesic effects of relaxation and meditation techniques.

Abbreviations

EMG, electromyography;
RIII-reflex, nociceptive flexion reflex;
NRS, numerical rating scale;
RSA, respiratory sinus arrhythmia

Keywords

Pain;
Breathing;
Analgesia;
RIII-reflex;
Autonomic;
Somatosensory evoked-potentials

Figures and tables from this article:

: Fig. 1. Experimental paradigm. Electrical stimuli (vertical black lines) were delivered during inspiration or expiration, and distributed in 3 conditions: A) 4s-inspiration slow breathing at a frequency of 6 breath/min (0.1HzSlowIns) B) 2s-inspiration slow breathing at a frequency of 6 breath/min (0.1HzFastIns) and C) regular breathing at a frequency of 12 breath/min (0.2Hz). High pitch and low pitch auditory cues indicated the beginning of inspiration and expiration (upward and downward black arrows). Stimuli were delivered 500 ms before the expiration cue or 1 or 2 seconds before the inspiration cue.; Figure options

: Fig. 2. Modulation of pain and anxiety ratings, RIII-reflex amplitude and N100 scalp evoked-potentials. Histograms represents the mean value and the SEM of (A) pain ratings, (B) shock-anxiety ratings, C) RIII amplitude presented in T-score and (D) N100 scalp evoked-potentials across the 6 conditions. Significant differences were found in pain ratings, RIII and N100 as reported in A, C and D (∗ p<0.05, ∗∗ p<0.01).; Figure options

: Fig. 3. Grand mean average of scalp evoked-potentials at Cz. The amplitude of the N100 component of the sural nerve potentials was decreased during the inspiration in the 0.1Hz-SlowIns condition. However, the P45, N150 and P260 were unaffected by respiration phase and frequency. The N100 component is indicated on the graph of the 0.1Hz-SlowIns condition.; Figure options