Respiration-induced hypoalgesia: exploration of potential mechanisms.

UNLABELLED Slow breathing is used as a means to reduce pain, yet the mechanisms responsible for respiration-induced hypoalgesia are poorly understood. The present study asked 30 healthy participants (M(age) = 21 years, M(education) = 15 years, 80% white non-Hispanic) to breathe at normal, slow (50% normal), and fast (125% normal) rates while constant-intensity, suprathreshold electric stimulations were delivered to the sural nerve to elicit pain and the nociceptive flexion reflex (NFR, a measure of spinal nociception). Stimulations were equally balanced across inhalations and exhalations to determine whether parasympathetic activation during exhalations contributes to hypoalgesia. Respiration rate, heart rate variability (HRV, a measure of parasympathetic activity), heart rate, and subjective arousal were assessed as manipulation checks. Slow breathing reduced pain relative to normal breathing and fast breathing, but NFR was not influenced by breathing. Further, pain and NFR did not differ between exhalations and inhalations, and changes in HRV did not correlate with changes in pain or NFR. Together, these findings suggest that respiration-induced hypoalgesia does not require gating of spinal nociception or changes in parasympathetic activity. PERSPECTIVE Slow breathing reduced pain relative to normal and fast breathing. This respiration-induced hypoalgesia does not appear to be due to gating of spinal nociception or changes in parasympathetic activity.