Neurophysiological evaluation of convergent afferents innervating the human esophagus and area of referred pain on the anterior chest wall.
Noxious stimuli in the esophagus cause pain that is referred to the anterior chest wall because of convergence of visceral and somatic afferents within the spinal cord. We sought to characterize the neurophysiological responses of these convergent spinal pain pathways in humans by studying 12 healthy subjects over three visits (V1, V2, and V3). Esophageal pain thresholds (Eso-PT) were assessed by electrical stimulation and anterior chest wall pain thresholds (ACW-PT) by use of a contact heat thermode. Esophageal evoked potentials (EEP) were recorded from the vertex following 200 electrical stimuli, and anterior chest wall evoked potentials (ACWEP) were recorded following 40 heat pulses. The fear of pain questionnaire (FPQ) was administered on V1. Statistical data are shown as point estimates of difference +/- 95% confidence interval. Pain thresholds increased between V1 and V3 [Eso-PT: V1-V3 = -17.9 mA (-27.9, -7.9) P < 0.001; ACW-PT: V1-V3 = -3.38 degrees C (-5.33, -1.42) P = 0.001]. The morphology of cortical responses from both sites was consistent and equivalent [P1, N1, P2, N2 complex, where P1 and P2 are is the first and second positive (downward) components of the CEP waveform, respectively, and N1 and N2 are the first and second negative (upward) components, respectively], indicating activation of similar cortical networks. For EEP, N1 and P2 latencies decreased between V1 and V3 [N1: V1-V3 = 13.7 (1.8, 25.4) P = 0.02; P2: V1-V3 = 32.5 (11.7, 53.2) P = 0.003], whereas amplitudes did not differ. For ACWEP, P2 latency increased between V1 and V3 [-35.9 (-60, -11.8) P = 0.005] and amplitudes decreased [P1-N1: V1-V3 = 5.4 (2.4, 8.4) P = 0.01; P2-N2: 6.8 (3.4, 10.3) P < 0.001]. The mean P1 latency of EEP over three visits was 126.6 ms and that of ACWEP was 101.6 ms, reflecting afferent transmission via Adelta fibers. There was a significant negative correlation between FPQ scores and Eso-PT on V1 (r = -0.57, P = 0.05). These data provide the first neurophysiological evidence of convergent esophageal and somatic pain pathways in humans.
Hobson
Anthony R
AR
Wingate Institute of Neurogastroenterology, Centre for Gastroenterology, Queen Mary's School of Medicine and Dentistry, 26 Ashfield St., London E12AJ, UK. a.hobson@qmul.ac.uk
Chizh
Boris
B
Hicks
Kirsty
K
Aziz
Qasim
Q
Worthen
Sian
S
Lawrence
Philip
P
Dewit
Odile
O
Boyle
Yvonne
Y
Dukes
George
G
D000328:Adult; D004947:Esophagus / Q000294:innervation* / Q000502:physiology; D005073:Evoked Potentials, Somatosensory / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009431:Neural Conduction / Q000502:physiology; D009619:Nociceptors / Q000502:physiology; D010147:Pain Measurement; D017288:Pain Threshold / Q000502:physiology; D053591:Referred Pain / Q000503:physiopathology*; D011930:Reaction Time / Q000502:physiology; D013116:Spinal Cord / Q000502:physiology*; D035441:Thoracic Wall / Q000294:innervation* / Q000502:physiology; D017833:Visceral Afferents / Q000502:physiology*