Pregnancy‐induced analgesia: a combined psychophysical and neurophysiological study

Abstract

In pregnant women, there is a progressive increase of heat pain threshold and a reduction of the CHEP amplitude, suggesting that a general inhibitory mechanism may be involved.

A Longitudinal Study to Evaluate Pregnancy-Induced Endogenous Analgesia and Pain Modulation

“…Our findings of no PIA effect with these static measures are in contrast with a study suggesting a progressive increase in heat pain threshold and a reduction of heat pain perception in pregnant women compared with nonpregnant subjects. 5 Our findings, however, support several studies showing no changes in static QST in pregnancy compared with postpartum. [3][4][5][6][7][8][9] Although CPM and mTS are reliable human experimental paradigms that measure dynamic components of pain modulation, 10,11,26 stability of these measurement tools repeated over prolonged time intervals as in this study is not well established.…”

“…Animal studies have demonstrated that gonadal hormones influence pain by modulation of the spinal cord dynorphin and κ opioid systems, [22][23][24][25] and that this phenomenon of pain inhibition can be abolished by blockade of spinal κ-opioid or δ-opioid receptors. 1 Although several animal studies studying PIA have shown significant pain modulation in the pregnant state, 1,2 studies evaluating PIA in women have used static QST, usually heat pain threshold and tolerance, [3][4][5] and have shown either no or a small effect. [3][4][5][6][7][8][9] Pain thresholds and tolerance may differ between animals and humans.…”

“…1 Although several animal studies studying PIA have shown significant pain modulation in the pregnant state, 1,2 studies evaluating PIA in women have used static QST, usually heat pain threshold and tolerance, [3][4][5] and have shown either no or a small effect. [3][4][5][6][7][8][9] Pain thresholds and tolerance may differ between animals and humans. Pain threshold (ie, when heat/cold becomes painful) may be influenced by human psychology and pain interpretation, and pain tolerance levels (ie, how long you can tolerate a painful stimulus) may be more impacted by human psychology and motivation compared with animal models.…”

“…1,2 Human studies evaluating the phenomenon of pregnancy-induced analgesia (PIA) have yielded mixed results. Several have demonstrated increases in heat pain threshold and tolerance during pregnancy compared with postpartum or nonpregnant control subjects, [3][4][5] whereas others have failed to show that PIA can be discerned with static quantitative sensory testing (QST). [6][7][8][9] Pain perception, however, is the result of dynamic and complex modulatory processes involving inhibitory and or excitatory nociceptive pathways; therefore, the magnitude of PIA and possible underlying mechanisms remain unsolved in human pregnancy.…”

“…Progressive inhibitory mechanisms are believed to be involved in PIA. 5 Mechanical temporal summation (mTS) is used to evaluate pain excitation pathway modulation. Reliable human experimental paradigms measuring these dynamic components of pain modulation have been developed.…”