The phenomenon of temporal summation to repetitive pressure pain stimuli is an important central neural mechanism for pain intensity encoding. This study evaluated the time-dependent behaviour of mechanical characteristics of soft tissue during repeated cuff stimulation used for eliciting temporal summation of cuff pressure-evoked pain. Such information of tissue mechanics is important for the interpretation of the pain response evoked during sequential stimulations.
Temporal summation was assessed in 16 subjects separated into two groups (healthy controls and severe knee osteoarthritis patients) using a visual analogue scale during 10 repetitive painful cuff stimuli (1-s duration, 1-s break) of the lower leg. The geometry of the lower leg was constructed based on magnetic resonance image (MRI) data. The loading boundary condition of the finite element model was defined according to the parabolic pattern of the interface pressure around the limb and the time-dependent profile of the cuff pressure during repetitive stimuli.
The pain intensity significantly increased with an increasing number of stimuli (p < 0.001), and facilitated temporal summation of pain was observed in patients compared with healthy controls (p < 0.001). The maximal deep tissue stress and strain during stimuli 1-4 varied 43% and 9%, respectively. No variation was observed for stimuli 5-10.
The temporal summation of pain during sequential cuff stimulation is inexplicable by the time-dependent response of mechanical stress and strain in soft tissue.
The study concludes that the temporal summation of pain response during sequential cuff pressure is not explicable by a specific time-dependent behaviour of stress and strain in the activated deep tissue and hence not due to changes in tissue biomechanics.