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Research Article

Neurophysiologic evaluation of convergent afferents innervating the human esophagus and area of referred pain on the anterior chest wall.

¹Queen Mary University of London ²

Submitted 17 July 2009 ; revision received 1 October 2009 ; accepted in final form 15 October 2009

ABSTRACT

Noxious stimuli in the esophagus cause pain that is referred to the anterior chest wall due to convergence of visceral and somatic afferents within the spinal cord. We sought to characterize the neurophysiologic responses of these convergent spinal pain pathways in man studying 12-healthy subjects over 3-visits (V1, V2 and V3). Esophageal pain thresholds (Eso-PT) were assessed using electrical stimulation and anterior chest wall pain thresholds (ACW-PT) using 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%CI. Pain thresholds increased between V1 and V3 (Eso-PT: V1-V3 = -17.9mA (-27.9, -7.9) p<0.001, ACW-PT: V1-V3 = -3.38ºC (-5.33, -1.42) p=0.001). The morphology of cortical responses from both sites was consistent and equivalent (P1, N1, P2, N2 complex) 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) whilst 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 3-visits was 126.6ms and for ACWEP was 101.6ms reflecting afferent transmission via A-fibres. 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 neurophysiologic evidence of convergent esophageal and somatic pain pathways in humans.

Cortical Evoked Potentials; Visceral; Somatic; Esophageal