Physiologically Induced State Anxiety Reduces Perceived Heat Pain in Healthy Subjects

BackgroundState anxiety modulates pain perception. Both, amplification and attenuation of perceived pain have been observed in healthy subjects in an acute state of anxiety, typically induced by phasic cues, such as threat of shock. However, state anxiety in real life is continuous over its duration. Here, this was experimentally achieved by administering hypercapnic air (7.5% CO2). The primary objective was to investigate whether perceived heat pain would be differentially modulated during this intervention compared to regular air administration. The secondary objective assessed the potential differences of such a modulation w.r.t. heat intensity level. Methods38 participants (19w) received two air mixtures (hypercapnic and regular air) for 13 minutes each, during which 18 (6x3) noxious heat stimuli of three different intensities were applied to the calf and had to be rated on two visual analogue scales (intensity and pleasantness/unpleasantness). State anxiety induction was assessed by comparing the body sensations questionnaire, self-assessment manikins, heart rate and galvanic skin response between conditions. Statistical analyses were performed using Bayesian estimation testing. ResultsBetween-condition differences were statistically meaningful for all heat intensity levels, always showing a reduced pain perception during hypercapnia compared to normocapnia. The magnitude of the observed hypoalgesic effect did not depend on heat intensity levels. ConclusionsPhysiologically induced continuous state anxiety results in hypoalgesia. Future studies need to determine whether the potentially involved neural mechanisms only reflect hypercapnic-dependent reactions in healthy subjects or generally represent anxiety-pain interactions in clinical pathologies.