Inter-individual differences in cardiovascular reactivity and the perception of the thermal grill illusion of pain

Background: Evidence has been given that there exists a functional relationship between the cardiovascular and the pain regulatory system. Alterations in blood pressure and concomitant changes in baroreceptor activation contribute to the modulation of pain sensitivity It could be shown that blood pressure, baroreflex sensitivity, and cardiac vagal tone (indexed by heart rate variability, HRV) are inversely associated to pain sensitivity. We aimed assessing the same cardiovascular parameters in a thermal grill paradigm to test the assumption of a relationship between inter-individual differences in autonomic cardiac control and the perception of the thermal grill illusion of pain (TGI).
Methods: All participants (N = 52) were stimulated three times during one minute with the temperatures of 15°C and 41°C set at the interlaced cold and warm bars of the water-bath driven thermal grill. Blood pressure and heart rate were recorded concomitantly. Numerical rating scales (NRS; 0–100) were used to quantify subjective paradoxical pain intensity and pain unpleasantness perceptions.
Results: A positive association between cardiac vagal tone and paradoxical pain sensitivity could be revealed. Higher resting HRV, as expressed by higher respiratory sinus arrhythmia (RSA), made it overall more likely to perceive the TGI. In contrast, blood pressure and the susceptibility to the TGI were inversely related. Volunteers displaying higher spontaneous blood pressure values in the first thermal grill stimulation phase did not feel the illusive pain as compared to those who presented significantly lower sympathetic arousal and perceived the TGI.
Conclusion: The present physiological findings complement previous evidence of an impact of psychological characteristics on the individual disposition to paradoxical pain perceptions.