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Despite medication with opioids and other powerful pharmacologic pain medications, most patients rate their pain during severe burn wound care as severe to excruciating. Excessive pain is a widespread medical problem in a wide range of patient populations. Immersive virtual reality (VR) distraction may help reduce pain associated with medical procedures. Recent research manipulating immersiveness has shown that a high tech VR helmet reduces pain more effectively than a low tech VR helmet. The present study explores the effect of interactivity on the analgesic effectiveness of virtual reality. Using a double blind design, in the present study, twenty-one volunteers were randomly assigned to one of two groups, and received a thermal pain stimulus during either interactive VR, or during non-interactive VR. Subjects in both groups individually glided through the virtual world, but one group could look around and interact with the environment using the trackball, whereas participants in the other group had no trackball. Afterwards, each participant provided subjective 0–10 ratings of cognitive, sensory and affective components of pain, and the amount of fun during the pain stimulus. Compared to the non-interactive VR group, participants in the interactive VR group showed 75% more reduction in pain unpleasantness (p < .005) and 74% more reduction in worst pain (p < .005). Interactivity increased the analgesic effectiveness of immersive virtual reality.
Despite aggressive use of pharmacologic analgesics, excessive pain during medical procedures performed on awake patients remains a widespread medical problem.1,2 Although increasing the dose of analgesics (e.g., opioids) often increases analgesia, side effects of the pain medications (e.g., nausea, constipation, cognitive dysfunction, disturbance of sleep cycles, etc) become increasingly problematic with higher opioid analgesia doses.2 Adjunctive use of psychological techniques such as distraction may help reduce patient suffering without increasing side effects.
Immersive virtual reality (VR) distraction provides computer-generated multi-sensory input (sight, sound, manual interactivity) to participants. There is growing clinical evidence that adjunctive use of VR reduces pain during interventions as disparate as burn-wound dressing changes, endoscopic urological procedures, and dental pain.3,4,5,6,7,8 Laboratory studies provide converging evidence that VR reduces pain. Functional brain imaging (fMRI) studies reveal that significant reductions in subjective pain ratings during VR immersion are accompanied by similar decreases in pain-related brain activity.9 And opioids + VR reduce pain ratings and pain-related brain activity more than opioid analgesia alone.10
Pain requires attention.11 Hoffman, Patterson and colleagues7 propose that VR is unusually attention grabbing, attracting the spotlight of attention into the virtual world, leaving less attention available to process incoming pain signals. As a result, many patients subjectively feel less pain, and spend less time thinking about their pain during medical procedures.
More immersive VR hardware is more effective at reducing pain.12,13,14 Hoffman, Seibel et al,12 showed that increasing the objective immersiveness of the VR system hardware increased the amount of VR analgesia obtained. In their study, one out of three healthy volunteers receiving thermal pain stimuli reported clinically meaningful reductions in pain (> 30% reductions) during VR via less immersive VR goggles (narrow field of view). In contrast, two out of three participants reported clinically meaningful reductions in pain in a group wearing a more immersive (wide field of view) VR helmet.12
Towards the goal of creating an immersive VR system,15 in the present study, our interactive VR group used a VR system designed 1) to shut out physical reality (helmet and headphones that exclude sights and sounds from the real world), 2) to provide converging evidence to multiple senses, (both sights and sounds), 3) to provide a surrounding/ panoramic view rather than limited narrow field of view, 4) to be vivid/high resolution, and 5) to permit the participant to interact with the virtual world via a trackball. Subjects in our non-interactive VR group used the same system, except with no trackball and thus no means to look around, aim and shoot to interact with objects in the virtual world. Slater and Wilbur15 define VR immersion as an objective, quantifiable description of what a particular VR system can provide to a participant. Immersion is different from presence in VR, the subjective psychological illusion of going into the virtual world. According to Slater and colleagues, presence is a psychological state of consciousness. Interactivity contributes to the objective immersiveness of a VR system. The current study is designed to isolate the influence of interactivity on analgesic effectiveness. Interactivity was the only factor manipulated.
Twenty-one subjects, 18–19 years of age, participated in a randomized, double-blind, between groups design comparing interactive VR vs. non-interactive VR. Both written and verbal informed consent were obtained using a protocol approved by the University of Washington’s Human Subjects Review Committee.
Controlled thermal pain stimulation was applied using a commercially available Medoc TSA II thermal pain stimulator (www.medoc-web.com) designed to provide noxious heat stimulation over a range of 0–50°C.16,17,18 The stimulus temperature (mean = 46°C, range = 44–48.5°C in the present study) was individually determined for each subject using the psychophysical method of ascending levels.9,13 A 30-sec heat stimulus (always 44°C for the first stimulus) was delivered through a thermode attached to the foot, and the subject was asked to rate the stimulus using a 0–10 graphic rating scale (see below). With the subject’s permission, the temperature for the next stimulus was then increased by 1°C (or less, if the patient was approaching his/her maximum) and again rated their pain. This sequence was repeated until the subject reported a stimulus that was “painful but tolerable.” The final stimulus temperature selected for the baseline pain condition (30-sec thermal stimulus without distraction) also served as the pain stimulus temperature during the subsequent VR intervention phase of the study protocol (30 sec of thermal pain during VR distraction).
After each pain stimulus, subjects received the following instructions prior to answering six separate subjective queries assessed with similar 0–10 graphic rating scales as shown below: “Please indicate how you felt during the past 30-sec pain stimulus by making a mark anywhere on the line. Your response does not have to be a whole number.”.
Such pain rating scales have been shown to be valid through their strong associations with other measures of pain intensity, as well as through their ability to detect treatment effects.19,20 The specific queries used in the current study were designed to assess the cognitive component of pain (amount of time spent thinking about pain), the affective component of pain (pain unpleasantness), and the sensory component of pain (worst pain). Nausea was assessed in an effort to identify the incidence of this component of simulator sickness sometimes associated with VR use.21 A single rating was used in the present study to assess the user’s sense of presence in the virtual world.
The VR system consisted of a Dell 530 workstation with dual 2 GHz CPUs, 2 GB of RAM, a GeForce 6800 video card, Windows 2000 operating system, and SnowWorld 2003 software (www.vrpain.com). The SnowWorld virtual environment presents a virtual arctic canyon to the user, complete with flowing river below, blue sky above, and terraced canyon walls to the sides containing virtual penguins, igloos, and snowmen. Soothing music and accompanying arctic sounds (e.g., the river) accompany the visual input (see Figure 1). Subjects in both treatment groups wore both a Kaiser SR-80 high-resolution head-mounted display with custom blinders to block subjects’ view of the real world, and noise-canceling headphones that provided background music and sound effects while excluding extraneous sounds of the immediate laboratory environment (see Figure 1).
Subjects in both treatment groups “glided” through the virtual world along a pre-determined path. Subjects in the interactive group could adjust their view of the vir- tual environment (e.g., subjects saw the sky when they looked up, a canyon wall when they looked to the left, and a river when they looked down). Subjects could target and shoot virtual objects on the canyon walls by moving the trackball. This interactive condition also included sound effects (e.g., a splash when a snowball hit the river; an animated green-, blue-, or white-colored explosion when a snowball hit the target). SnowWorld was specifically designed to have a simple human-computer interface for burn patients who often have reduced attention resources and limited dexterity available during wound care (due to pain, opioid medications, and burn injuries to the hands).
The non-interactive VR system (hardware and software) in this group was identical to the interactive VR system, with the exception that subjects could not interact with the virtual world (i.e., could not use the trackball to look around the virtual world or target/shoot virtual targets).
Data for each outcome variable were analyzed using SPSS by One-Way ANOVA, and are reported as means with SD in parentheses after each mean.
The baseline (i.e., with no VR) thermal pain stimulation temperatures were equivalent for the interactive and non-interactive groups [mean temperature of 46.0 °C (SD = 1.1 °C) and 46.2°C (SD = 1.1°C) respectively, F(1,19) = .10, p = .75 NS]. The VR analgesia scores (baseline pain minus pain during VR) were calculated for each individual (max possible difference = 10) for each of the three pain ratings, (i.e., worst pain, pain unpleasantness, and time spent thinking about pain). These VR analgesia scores were analyzed using between-groups analysis via One-Way ANOVA, with alpha = .05. The results are summarized in Table 1.
As can be seen in more detail in Table 1 (B minus VR), subjects in the interactive VR group reported a significantly larger reduction in pain unpleasantness during VR compared to subjects in the non-interactive VR group [mean = 3.43 (1.97) vs. .86 (1.39) respectively], F(1,19) = 11.11, p < .005, MSE = 3.06.
Subjects in the interactive VR group reported a significantly larger reduction in pain intensity (ie., worst pain) during VR compared to subjects in the non-interactive VR group [mean = 3.21 (1.64) vs. .82 (1.38) respectively], F(1,19) = 12.45, p < .005, MSE = 2.35.
Subjects in the interactive VR group did not report a significantly larger reduction in time spent thinking about pain during VR, compared to subjects in the non-interactive VR group [mean = 4.16 (1.59) vs. 2.83 (1.93) respectively], F(1,19) = 2.99, p = .10 NS, MSE = 3.03.
Subjects in the interactive VR group reported a significantly larger increase in “fun” in VR compared to subjects in the non-interactive VR group [mean = 3.45 (1.53) vs. 1.83 (.90) respectively], F(1,19) = 7.86, p = .01, MSE = 1.71.
And no significant difference between the groups was found for ratings of how present participants felt in virtual reality [4.1 (1.7) vs. 3.0 (2.0) for non-interactive and interactive respectively, F(1,19) = 1.82, p = 0.19, NS, MSE = 3.57], or how nauseous participants felt in virtual reality, nearly zero nausea [.04 (.05) vs. .08 (.17) for non-interactive and interactive respectively, F(1,19) < 1, p = .50 NS, MSE = .014].
In this study, we compared the relative effectiveness of VR distraction using an interactive VR system vs. a non-interactive VR system. Results showed more pain reduction during interactive VR than during non-interactive VR. Compared to the non-interactive group, the interactive VR group reported 32% more reduction in time spent thinking about pain, 75% more reduction in pain unpleasantness, 74% more reduction in worst pain, and 47% more increase in fun during VR. Our findings using a highly immersive VR system with 19–20 year old college students during thermal pain are consistent with those reporting enhanced analgesia when interactivity is added to a less immersive VR system using a video game in children experiencing cold pressor pain.22 The results of the present study provide converging evidence for the importance of subject interaction with the virtual world for maximizing the amount of VR analgesia, and implicate involvement of an attentional mechanism in VR analgesia.
Increasing the immersiveness of the VR system significantly increased the analgesic effectiveness without a significant increase in presence ratings (see also Hoffman et al).12 Pain ratings may be more sensitive to manipulations of the immersiveness of VR hardware, compared to the single VAS presence rating scale typically used in most VR analgesia studies. In the studies to date, manipulations of the immersiveness of VR systems consistently affected the amount of pain reduction achieved. Several custom VR systems that don’t allow head movements (using a mouse or trackball to look around and interact with the virtual world, as in the present study) have achieved large reductions in pain (e.g, water friendly fiberoptic VR goggles,3 fMRI magnet friendly fiberoptic VR goggles,9,10 and articulated arm mounted VR goggles). 4 Unlike interactivity and helmet quality, we speculate that head tracking may be one factor affecting the immersiveness of the VR system that does not strongly affect analgesia.
Research is needed to further explore what elements of immersive VR are dispensible and how to maximize VR analgesia. The present results support the notion that maximizing the immersiveness of the VR systems will help maximize VR’s analgesic effectiveness. Future studies exploring how to best combine VR and pharmacologics in a multimodal approach to analgesia are justified.
Pain during medical procedures such as severe burn wound care is often excessive. Adjunctive use of immersive virtual reality can substantially reduce the amount of procedural pain experienced. The results of the present study show that a more immersive interactive VR system reduced pain more effectively than a less immersive, non-interactive VR system.
We thank the undergraduate students who participated in this study, as well as Christine Hoffer for her logistic assistance in performing the study. This work was supported by NIH HD40954-01, 1R01AR054115-01A1, R01 GM042725-17A1, the Scan Design by Inger & Jens Bruun Foundation, and the Pfeiffer Foundation.
The authors have no potential conflicts of interest to disclose.