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When designing
studies of constipation among those being treated for illness, especially those
receiving palliative care, it is important to consider the relative roles of:
- Dietary
fiber, food intake and physical activity
- Mental
state
- Opioid
contribution to constipation, and
- Opioid
tolerance.
Dietary
fiber, food intake, and physical activity
The influence
of dietary fiber on gut transit and ease of defecation emerged from comparative
epidemiological studies on groups with different dietary habits (Burkitt,
Walker and Painter, 1972). On the other hand, the efficacy of adding fiber
to the diet of a constipated person depends on the type of fiber and the degree
of constipation, especially the duration of transit time. A study of constipated
cancer patients found that it would take an intolerable increase in dietary fiber
to produce a significant improvement in bowel frequency (Mumford,
1986).
Most colonic
activity consists of segmentation, which mixes the contents but produces no net
forward movement. Peristalsis occurs on only a small number of occasions each
day and may then produce transit over considerable distances. Manometric studies
in healthy subjects have shown that these mass movements are grouped after:
Peristalsis
and colonic transit are, therefore, strongly influenced by:
No direct studies
of the pattern of transit alterations in a medically ill population have been
reported. Such studies present difficulties because of their invasiveness in a
group who are unwell for reasons separate from any bowel pathology.
In fit people
it has been hard to show an influence of physical activity on
gut motility. Total and colonic transit was unaltered in healthy
volunteers by treadmill exercise (Robertson
et al., 1993). In athletes, small bowel transit time was not
influenced by imposed rest (Kayaleh
et al., 1996).
An indirect
approach was used in a group of cancer patients whose constipation,
assessed by a simple categorical scale, showed a highly significant
correlation with poor (3 or 4) ECOG performance scale results
(Fallon
and Hanks, 1999). Clearly, such an approach cannot clarify
whether immobility or some other influence on gut transit is most
influential, or which gut regions are most affected.
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