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Level
2: Characterization
of Model Phenomena
As a next
step, the investigator has to measure and summarize the signs
and symptoms that occur in response to the stimulus applied by
the pain model system. Assuming that there is no valid case definition,
such as a biomarker of sufficient sensitivity and specificity
for the clinical condition in question, symptoms and signs in
response to pain are measured and compared using the same assessment
techniques and strategies employed in the clinical material (Level
1).
Varying the stimulation
parameters sheds additional light on factors that regulate or
modulate the signs and symptoms in response to pain. Non-painful
stimuli should be employed in a blind fashion as a control to
tease out the effects specific to pain from those that are non-specific,
such as responses due to the subject's anticipation of pain. Additional
attention should also be devoted to the temporal sequence of events
by which signs and symptoms appear in response to pain as those
measures can rarely be obtained in clinics. Such observations
can provide important insight into the pathogenesis of the clinical
picture that is not easily understood in a clinical context because
signs and symptoms present at once and their temporal relationships
are not easily resolved.
| Figure
13.1: Level 2 of Model Validation Process
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A,
B and C refer to variations in the model conditions.
Internal validity is assessed by contrasting
symptoms reported in experimental pain with
the corresponding signs measured by the investigator.
Mismatch between these findings would constitute
questionable validity. Observations of the temporal
sequence of events by which signs and symptoms
occur in response to pain provide insight into
the pathogenesis of complex clinical scenarios.
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