The extent and time-frame of endogenous inhibitory effects after a cold pressor test using a conditioned pain modulation paradigm (ICE study)

Several studies suggested the necessity of using painful stimuli as
conditioning and as test stimuli to produce inhibitory effects. However,
non-painful heat as conditioning stimulus also appeared to be capable of
decreasing the ratings of the test stimuli at painful levels (Stefan
Lautenbacher, Roscher, & Strian, 2002). Whether the subjective painfulness of
the conditioning and the test stimuli forms a prerequisite for the inhibitory
action has not yet been investigated in a systematic fashion although
inhibitory effects upon non-painful sensations have been observed. The
conditioning stimuli in most studies were mainly not assessed for their
perceptual qualities. In one study they utilized two conditioning stimuli
(heat pain) both very close to pain threshold, one above and one below (S
Lautenbacher & Rollman, 1997). Interestingly, these two (heat) stimuli did not
differ in their inhibitory effects. In the NAP study we utilize a cold pressor
test as conditioning stimulus in accordance with conditioned pain modulation
paradigm guideliness described in literature. As far as we know, to date there
is no study available that investigated the necessity of using a cold pain
tolerance threshold to produce inhibitory effects. Several (above-mentioned)
studies suggested less pain stimuli might be capable to reliably activate
endogenous inhibitory pathways, and therefore unnecessary to expose study
subjects to more painful stimuli. In this sub-study we will explore whether
the inhibitory effects of conditioned stimuli depent on the subjective
experience of pain. Furthermore, we will explore the time-frame of these
inhibitory effects.

In this sub-study we will explore whether the inhibitory effects of conditioned
stimuli depent on the subjective experience of pain. Furthermore, we will
explore the time-frame of these inhibitory effects.

prospective, observational, mono-center study

-2 test sessions

Study subjects will undertake a 30-minute experiment at visits at the Intensive
Care Unit Department. Quantitative sensory testing will be performed, including
evaluation of endogenous analgesia pathways (conditioned pain modulation) using
a cold pressor test (CPT). Risks during participation in this study are
negligible. Study session will be performed at the Intensive Care Department.
The study will not intervene with daily habits of participating residents.
Nocitrack® device used for eQST measurement is approved safe by the Department
of Medical Physics of the St. Antonius Hospital [Device number 66294]. ECG
electrodes attached to the skin during the use of the Nocitrack® device might
give some local skin redness or irritability, however based on former clinical
use this is expected to be minimal. Benefit exists in expanding our knowledge
about the effects of sleep deprivation on several pain processes.