| |
Any model of pain
for human application should be safe and reliable. The pain challenge
should also be applied to deep tissue, such as muscle, because,
in contrast to superficial pain, deep pain is poorly localized
and frequently associated with pronounced autonomic responses
(Cervero, 1988; Gebhardt
and Ness, 1991).
Deep pain in tissue
such as muscle has been induced in humans by experimental techniques
such as fatiguing concentric and eccentric muscles, ischemia,
and electrical stimulation. Pain has also been induced in deep
tissue by injection of algesic substances that are suitable for
human use. Although heat has been applied directly to deep tissue
in experimental animals, thermal stimulation is unlikely to gain
acceptance in the study of deep somatic pain in humans because
of tissue damage. Visceral pain conditions have been modeled by
systems using mechanical distention or electrical stimulation.
Since pain sensitivity
and ability to suppress pain vary widely between individuals,
a stimulus of a given magnitude is likely to result in significant
response differences between subjects. This variation may need
to be taken into account in the design of the model conditions
and interpretation of results. With this background in mind, differences
in model conditions need to be understood within the context of
the question that the investigator aims to study.
| Table
6.1: Stimulus and Subject Response
|
|---|
| Stimulus
Type
| Pain
Stimulation
| Resulting
Pain Experience
|
|---|
| Single | Brief
or Initial | Inter-individual
differences in pain intensity |
| Repeated
Constant magnitude | Prolonged | Inter-individual
differences in pain intensity and time course of pain |
| Continuous
Experientially-adjusted | Sustained | Similar
intensity and time course of perceived pain among subjects |
|
|