Heart rate variability as a measure of pain intensity in healthy volunteers

Pain is considered to be multifactorial. It consists of physical pain -somatic,
visceral and/or neuropathic-, psychosocial, emotional and spiritual pain. When
measuring pain intensity, the pain experience of a patient is measured. This is
subjective as only a patient can describe how he experiences his pain. In the
clinic, the visual analogue scale (VAS) is the standard tool to measure pain
intensity. This is a scale ranging from 0 (no pain) to 10 (the worst pain
imaginable). The patient can indicate his pain intensity at a specific moment.
It is an easy tool to use in the (outpatient) clinic, but it has several
disadvantages: it needs patient*s understanding and co-operation, it is
subjective and the reproducibility over time is limited. Moreover, an
assessment of pain with the VAS for one patient may not imply the same
intensity in another patient.
In patients unable to communicate their pain changes in heart rate and blood
pressure are sometimes used to measure pain intensity. Heart rate variability
is one of these methods. Heart rate variability is easy, reproducible and
objective to measure. Most studies using heart rate variability as a measure of
pain intensity have been performed in infants, mostly admitted to a NICU, and
pain scores have been taken by trained nurses.
Therefore, to which extent heart rate variability is a measure of pain
intensity should be further explored.

The objective of this study is to determine whether heart rate variability
measures correlate with pain intensity measured by a visual analogue scale in
healthy volunteers in whom pain is induced by local heat application.

Healthy volunteers will be asked to participate in this study.
Volunteers will be asked to fill in the neuroticism subscale of the Eysenck
Personality Questionnaire before the start of the procedure.
At baseline, pain intensity will be assessed by visual analogue scale. Heart
rate will be measured continuously during the whole research period (about 30
minutes) using a Portapres. After obtaining five minutes of baseline heart rate
recording, pain will be induced using local applied heat to the forearm. This
stimulus will be continued during two minutes. After which volunteers will
indicate on a VAS the intensity of the experienced pain. Thereafter, ten
minutes of rest will be followed by application of the same pain stimulus and
pain measurement. This procedure will be repeated twice.

The Medoc Pathway System (Medoc ltd., Israel) equipment will be used to apply
heat to the inner forearm. Before starting pain measurements the thermode will
be placed on the forearm of the arm NOT containing the Portapres equipment
necessary to measure the heart rate. This electrode is connected to the Pathway
equipment which is programmed to induce heat during 2 minutes, starting at 45
degrees Celsius increasing every 10 seconds with 0.1 degree Celsius during
those two minutes. This will provide a stable pain intensity measured by the
visual analogue scale.

-30 minutes time
-a moderate pain during apllication of the pain stimulus
-possible redness where the thermode has been placed