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In 1637 Rene Descartes wrote “The soul by which I am, what I am, is entirely distinct from my body and even if the body were not, the soul would not cease to be what it is”.1 Descartes was thus reflecting on the longstanding conundrum of relationships between body and soul which have continued to this day and are equally mirrored in our views on diseases of the gastrointestinal tract.
The fathers of gastroenterology clearly recognised the relationships between the brain and gut. In his classic studies of the control of gastric secretion conducted on his subject Tom with a permanent gastric fistula,2 Stuart Wolf found that emotional state affected secretion and that mucosal blood flow, measured by a simple thermistor, altered in parallel.3 Similar relationships between rectal mucosal blood flow and psychological state were also reported by Almy.4 In his now classic “hoax” experiment, he induced anxiety in a “volunteer” by pretending to identify an abnormality during sigmoidoscopy. This induced a marked change in colonic motor activity and a change in mucosal colour.
In the last half century however the onset of an era of objectivity has influenced how we view gastrointestinal symptoms. Quite rightly perhaps, the view that “if you can't measure something you don't know that it exists” has entered gastroenterology. As a result of this scientific rigour, the validity of observations such as those of Wolf and Almy have understandably been questioned. “Where are the controls in a case report?” “What is the repeatability of a hoax?”
A consequence of this objectivity has been that research has become concentrated on that which can be accurately measured and avoidance of that which cannot, irrespective of its relevance to the problems of clinical practice. The pendulum of research endeavour thus swung away from mind-gut interactions over the last half century. Paradoxically however the development of more and more objective technologies for measuring gut function have now begun to return the pendulum to a more balanced position. Thanks to the development of new and powerful brain imaging techniques such as positron emission tomography and functional magnetic resonance imaging, research over the last decade has shown remarkable insights into relationships between the brain and gut.5
The recent work by Emmanuel and Kamm6 ,7 represents a further advance in the measurement of brain-gut activity. Using a sensitive laser Doppler flowmeter they measured rectal mucosal blood flow to a high degree of accuracy and showed that it changes in a predictable manner with meal ingestion and in response to pharmacological agents. In their current work8 ,9 they have re-explored the work of Almy and Wolf and now report the relationships between psychological state and gut mucosal blood flow and the results of behavioural treatment (biofeedback) in patients with constipation (see pages 209 and 214).
What Emmanuel and colleagues8 ,9 have found is that rectal mucosal blood flow correlates well with degrees of anxiety/depression expressed in patients with chronic constipation. They have also shown that in patients who respond to behavioural therapy (biofeedback) there is an associated “improvement” in mucosal blood flow. So what does this tell us about Cartesian dualism in functional bowel diseases such as constipation? The results clearly show that it is naïve to continue with the belief that because patients have gut symptoms they must therefore have a gut (and not a brain) disorder. Indeed their studies could be interpreted to indicate that most if not all of the problem in functional gastrointestinal disorders arises from the brain. The real answer is of course not so simple. The reports do not exclude the possibility that a gut located disorder (for example, intrinsic neural damage) could play an important role in the development of constipation.8 ,9 However, their interesting findings suggest strongly that whatever the primary cause may be, blood flow changes in constipation are not themselves modulated by the degree of constipation but are related to anxiety levels expressed in patients.
One of the continuing difficulties in studies of the brain-gut axis in patients with functional gastrointestinal disorders remains the influence of the technique used for studying gut function on the variable being studied and the work of Emmanuel et al, while taking us forwards from the studies of Almy, is still subject to this problem. Measurement of rectal mucosal blood flow by their technique requires rigid sigmoidoscopy for probe placement, and hence those individuals who find rigid sigmoidoscopy a distressing procedure would no doubt show greater alterations in rectal mucosal blood flow during the procedure than those who do not. This is perhaps one explanation for the stronger relationship between anxiety state and rectal mucosal blood flow in constipated patients. The fundamental question of whether constipation is a gut manifestation of an altered psychological state or a psychological manifestation of altered gastrointestinal state therefore unfortunately remains unanswered.
Do the studies of Emmanuel et al on biofeedback help us unravel this problem? The paper9 shows that effective behavioural therapy (biofeedback) improves both symptoms and rectal blood flow in 60% of constipated patients. Does this therefore indicate that colonic function is improved by biofeedback? While it is reassuring to note that patients feel better, constipation itself seemed to be more difficult to move, and marker transit showed only a small improvement. Here again the relationship between the measured variable and its effect on the measurement becomes relevant. In the study of Emmanuel and Kamm, improvement in rectal mucosal blood flow could only be noted at the time of sigmoidoscopy, which perhaps could simply indicate that biofeedback increased patient tolerance to sigmoidoscopy!
While the studies of Emmanuel et al on CNS control of mucosal blood flow8 ,9 are a valuable advance and place our understanding of mind-body relationships on a yet more objective footing, they inevitably raise as many questions as they answer, and the problem of Descartian dichotomy is not yet completely resolved for functional disorders. If the gut had its own mind and could express its views about the conundrum, perhaps it might paraphrase Descartes' famous maxim and respond in the following manner: “I'm pink, therefore I am”.
- Motility and visceral sensation
- Motility and visceral sensation