Studies of human psycho-physiological responses to visceral pain.

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Nature of proposed research: while pain is a common human experience, our tolerance to it varies. This is because factors that influence pain perception such as life experiences, mental state and our genes, differ between individuals. Furthermore, when we perceive pain different parts of the nervous system are activated. These include nerves that carry pain signals from the body to the brain, control organ function e.g. heart and gut, and those that control the secretion of hormones such as cortisol that help combat stress. In our preliminary studies, we induced pain by blowing up a balloon in the healthy human oeosphagus (gullet) while we measured the activity of nerves that control the heart. We demonstrated that the activity of the vagus nerve which slows down the heart increased in some subjects and decreased in others. Interestingly, subjects who showed an increase in activity were in general more anxious and worried than those who showed a decrease in activity. These results suggest that two distinct populations exist in the way they respond to pain. We now want to carry out studies in a larger number of subjects to determine how prevalent the two types of responses to pain are and also to determine whether a particular response in an individual is reproducible over time. Furthermore we want to determine whether the hormonal response (cortisol levels) to stress is different in the two types of individuals and whether they also differ in the degree to which their oesophagus becomes sensitive after injury with acid. Finally we want to determine if patients who have chronic pain arising from the oesophagus but in whom no cause can be identified also demonstrate the same two types of response to pain as healthy subjects. We will also determine whether individuals who behave differently to pain do so because they have different genes from others. Prospective outcomes: we anticipate that this research will improve our understanding of why individuals differ in their response to pain and also whether certain individuals are more likely to developing chronic pain conditions. Expected benefit to human health: if certain individuals are more at risk of developing chronic pain then treatment strategies can be developed based on the reasons leading to this increase in risk, and preventative measures can then be taken to protect these individuals from environmental influences that may predispose them to the development of chronic pain conditions.