Pain and Unpleasantness Evoked by a Cold Pressor Test: METHODS

In: Main

10 Mar 2010


Thirteen healthy male undergraduate students were enrolled as one group and 11 female undergraduate students entered the study as another group. They were recruited by bill posting. All of the volunteers were healthy and used no medication. They had no previous experience with video glasses or cold pressor pain. The effect of video glasses was explained to the participants using the following neutral information: “Video glasses are today used widely for amusement of dental patients. Preliminary studies have shown a decrease in the feeling of unpleasantness among approximately half of these patients.” The cold pressor test and the experimental set-up were explained in writing, and students were informed that they could stop the experiment at any time. Written informed consent was obtained according to the Helsinki Declaration. The mean age (±SD) for the male group was 23.7 years (±3.3; range 21-33 years) and for the female group was 24.5 years (±2.1; range 23-30 years).


The cold pressor equipment consisted of a cold-water tank with a water temperature of 1-2°C. In the center of the tank was placed a perforated cylinder that separated the ice from the water inside the cylinder, allowed the water to circulate freely, but avoided direct skin contact with the ice. The video equipment consisted of a video recorder (NV-HD 660 Panasonic®) connected to a pair of video glasses (I-Glasses®, Virtual i-O®, Seattle, WA) used to transmit the video to the volunteer (the Figure). A 3D video sequence showing roller skaters and a comparable 2D video sequence were used.

Experimental Design

The study was designed as a controlled, randomized experiment. The study consisted of three trials using 3D, 2D, and no video glasses (control). The subjects were randomized prior to the experiment to start with either 3D, 2D, or no glasses. The volunteer was placed in a comfortable chair beside the cold water tank, the video glasses were mounted, and a test was conducted to ensure optimal reception of picture and sound from the video sequence. The volunteer immersed the left hand completely into the water tank. The left hand was used for immersion every time, as a previous study has shown that there is no difference in pain ratings using either the dominant or nondominant hand during a cold pressor test. The hand was not strapped, allowing the volunteer to withdraw the hand if the sensation became unbearable. After 3 minutes (or sooner if the sensation was unbearable), the volunteer withdrew the hand and was allowed to dry it with a towel. When the volunteer indicated that the hand had returned to its normal temperature, the next trial was performed. The intertest period was a minimum of 15 minutes, during which the volunteer was allowed to exercise the hand and warm it with a hair dryer. Immediately after each cold pressor test was completed, the volunteers scored their perceived pain intensity and unpleasantness on 100-mm VASs. The VASs were labeled with the statements “not at all painful” and “extremely painful” or “not at all unpleasant” and “extremely unpleasant” at either end. After the third trial, the volunteers were finally asked which of the three options, ie, 3D video, 2D video, or no video, they would prefer if they had to participate in another cold pressor test. The volunteers were not told of any positive effect of the video glasses, and they were not able to manipulate the picture quality nor to control the volume of the music after the adaptation period. The experimenter was present in the room during the trials in order to monitor the subjects but did not communicate with them.


Within each group (males and females), the VAS scores for each trial were compared by the Wilcoxon signed-rank test. The groups were compared using the Mann-Whitney U test for differences in VAS scores between genders. P < .05 was accepted as a significant difference. Viagra Online Canadian Pharmacy

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