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Pregnancy‐induced analgesia: a combined psychophysical and neurophysiological study
Author(s) -
Draisci G.,
Catarci S.,
Vollono C.,
Zanfini B.A.,
Pazzaglia C.,
Cadeddu C.,
Virdis D.,
Valeriani M.
Publication year - 2012
Publication title -
european journal of pain
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.305
H-Index - 109
eISSN - 1532-2149
pISSN - 1090-3801
DOI - 10.1002/j.1532-2149.2012.00139.x
Subject(s) - dermatome , medicine , threshold of pain , forearm , pregnancy , anesthesia , surgery , biology , genetics
Background To investigate changes in heat pain threshold and modifications in heat pain processing during pregnancy and labour, seventy‐six nulliparous pregnant women were enrolled in two studies. Methods In the first study (psychophysical), 60 pregnant women underwent a quantitative sensory testing ( QST ) investigating heat perception in two body areas (right forearm and T 10 dermatome) according to these groups: 32–33 gestational weeks ( GW ), 39–40 GW , early stage of active labour and 24 h after the delivery. In the other study (neurophysiological), contact heat‐evoked potentials ( CHEPs ) were recorded in other 16 women at the 32nd GW and in 11 of these also at the 40th GW . Results The psychophysical study showed that heat pain threshold was significantly increased at the forearm at 32–33 GW (median ± IQR : 39.6 ± 0.7 ° C ), at 39–40 GW (40.6 ± 1.1 ° C ) and at early stage of active labour (40.8 ± 1.5 ° C ) as compared to 20 non‐pregnant controls ( p < 0.001). Heat pain threshold tested at T 10 level was significantly increased at 32–33 GW (41.0 ± 1.6 ° C ), at 39–40 GW (42.1 ± 1.8 ° C ), and at early stage of active labour (42.3 ± 1.3 ° C ) as compared to the non‐pregnant women ( p < 0.001). The N 2‐ P 2 CHEP amplitude (main negative N 2 and positive P 2 components of the vertex biphasic potential) recorded from the pregnant women was significantly lower at the 40th than at the 32nd GW , after stimulation of both the forearm ( p < 0.001) and the abdomen ( p < 0.001). Conclusions 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.