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Session: Poster session I
Session starts: Thursday 24 January, 15:00

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Marit van Velzen (Dept of experimental Anesthesiology, Erasmus University Medical Center Rotterdam)
Minke Kortekaas (Dept of experimental Anesthesiology, Erasmus University Medical Center Rotterdam)
Arjo Loeve (Biomechanical Engineering, faculty 3mE, Delft University of Technology)
Egbert Mik (Dept of experimental Anesthesiology, Erasmus University Medical Center Rotterdam)
Sjoerd Niehof (Dept of experimental Anesthesiology, Erasmus University Medical Center Rotterdam)
Robert Jan Stolker (Dept of experimental Anesthesiology, Erasmus University Medical Center Rotterdam)

Abstract:
INTRODUCTION Pain is usually assessed by the interpretation of behaviour of and/or reports by patients. Both methods bear subjective elements. Having purely objective pain assessment tools would greatly benefit clinical practice. Vasoconstriction is one of the physiological responses of the body to pain. Vasoconstriction changes the arterial compliance (index of arterial elasticity). The compliance can be determined using photoplethysmography (PPG).During vasoconstriction, the blood velocity increases when the blood flow is kept constant despite the reduced arterial diameter, and the arterial compliance decreases. Consequently, the time it takes for a pressure pulse wave (PW) to travel from the heart to the periphery (called the pulse transit time, PTT) decreases. The PTT is determined by taking the time between the R-wave of the ECG and the arrival of the foot of the PW in the fingertip. The PW in the fingertip can be visualized using PPG, a widely available non-invasive technique for measuring PWs with a simple photodiode and infrared light. Theoretically, the vasoconstriction in response to a pain stimulus causes a decrease of PTT. The aim of our study is to investigate if the PTT decreases in response of heat induced pain stimuli. METHODS The PTT was measured in healthy volunteers (18-35 years of age, no cardiovascular or other vasomotor function affecting disease, no limb injuries) on both index fingers, using PPG-sensors. Baseline PTT was measured for 1 minute while the subjects were sitting relaxed without moving. To test if the PTT decreases due to a vascular response to pain, the subjects received a heat-induced pain stimulus, which was applied using a temperature control block (thermode). Each stimulus started at a temperature of 32°C and rose to 50°C with a speed of 1°C/s. The temperature of the thermode was set to drop back to the starting temperature of 32°C with a speed of 10°C/s after each stimulus. To explore the best way to measure the repeatability of PTT measurements, the stimulus was applied 3 times with a time interval of 20 or 60 seconds (randomized). Afterwards, the relative PTT change between the last heartbeat before and the first heartbeat after each the stimulus was determined. RESULTS Three subjects were included for the pilot study (2 men and 1 woman, age 29 ± 4.5 years (mean ± SD), BMI 22 ± 2 kg/m²) and a mean difference in PTT of –7.7 ± 0.71% on the stimulated side was found. CONCLUSION Preliminary results suggest that PTT decreases in response to heat-induced pain stimuli. After the approval of the METC Ethical board, expected early October 2012, 20 subjects will be measured. It is expected that PTT can be used as an objective indication of pain.