VALIDATION OF DIGITAL INFRARED THERMAL IMAGING (DITI) WITH CONTACT THERMOMETRY: PILOT DATA
Cameron van den Heuvel, Sally Ferguson, Saul Gilbert and Drew Dawson
Centre for Sleep Research,University of South Australia, Australia.
Assessment of skin surface temperatures in the research laboratory has traditionally required attachment of thermistors that can limit subjects' movement and comfort. Especially during sleep studies, this can confound the results by delaying sleep initiation or increasing wake after sleep onset. However, remote sensing of temperature using a digital infrared thermal imaging (DITI) system can eliminate this potential confound. The aim of this study was to validate the temperature data from a new DITI system against a contact thermometry system already in use in our sleep laboratory.
At the time of submission, pilot data consisted of 184 measures of hand skin temperature (Tsk) collected and analyzed from one volunteer. Skin thermistors (Steri-Probe type 499B, Cincinnatti Sub Zero, Cincinnati OH) denuded of adhesive foam backing were attached with a minimal amount of adhesive to eight locations on the fingertips and palms of the subject's right hand. At various times of the day, after a 15-minute period of seated rest, data was collected simultaneously during 30-second intervals using a DITI system (MMS Med2000, Meditherm, QLD Australia) and a custom temperature system (Strawberry Tree) - both sensitive to temp changes of 0.01 deg C. Sixteen of the 184 Tsk measures could not be analyzed for technical reasons; the remaining data were analyzed using simple regressions and t-tests.
Preliminary results indicate that Tsk obtained using DITI displays a very strong and significant relationship with thermistor data at all locations investigated. In comparison to contact thermometry, DITI temperature data was precise but consistently lower by an average of xx deg C over all measures.
It is anticipated that calibration of both systems to "black box" temperature emitters and increased sample size would further strengthen the relationship between data obtained. Nevertheless, the data analyzed to date demonstrate that DITI is a useful tool for assessing skin surface temperatures in the sleep laboratory.
DIFFERENTIAL CHANGES IN SLEEP ONSET LATENCY, PERIPHERAL AND CORE BODY TEMPERATURES FOLLOWING CAFFEINE AND TEMAZEPAM ADMINISTRATION
S.S. Gilbert, S. Ferguson, C.J. van den Heuvel, A. Holmes and D. Dawson
Centre for Sleep Research, University of South Australia, Australia.
Sleep onset latency has been linked with a rapid reduction in core body temperature (TC) through increased peripheral heat loss 1. However, as the analysis of peripheral temperature physiology has been limited to single temperature thermistors attached to discrete body areas, it has not been possible to observe sleep onset-related changes in peripheral temperature in an integrated or cohesive manner. Recently, however, low cost high resolution thermal imaging systems have become available enabling the measurement of real-time changes in peripheral temperature across the whole body simultaneously 2. By using thermal imaging as well as standard thermistors and employing both an alerting agent (caffeine) and hypnotic agent (temazepam) to manipulate sleep propensity, we aimed to determine whether the capacity to dissipate heat at both proximal and peripheral skin sites may affect sleep onset in young adults. Preliminary results from four male subjects (18-23y) have been obtained thus far and only the thermistor data have been analysed. For these subjects, the thermoregulatory and soporific effects of temazepam (20mg) were compared. with caffeine (100mg), both given orally at 1400h. The study was placebo-controlled and counter balanced. From 0900-1830h, subjects lay quietly in bed during which time, skin and rectal temperatures were recorded continuously. Sleep propensity was measured using 30 minute multiple sleep latency tests (MSLT) performed hourly from 1100-1800h. Subjects were scored as being asleep after 3 consecutive epochs in stage 1 sleep (SOL1). Infra-red thermal images of the upper body (torso, head, arms and hands) were also taken during the MSLT protocols. Repeated measures ANOVAS were used for statistical analyses. Following temazepam administration, significant reductions in both TC (-0.23°C) and SOL1 (-11.6min) as well as a significant increase in foot temperature (0.86°C) were observed relative to placebo. Following caffeine administration, a significant increase in SOL1 (11.8min) and significant decrease in foot temperature (-2.05°C) were observed relative to placebo while TC did not differ significantly from placebo. For both caffeine and temazepam, a significant (p<0.05) Pearson's correlation coefficient of -0.49 was obtained between changes in SOL1 and foot temperature. From these results it could be argued that a decrease as well as an increase in peripheral heat loss may be involved in the regulation of sleep propensity.
Krauchi K., Cajochen C., Werth E., Wirz-Justice, A. Warm feet promote the rapid onset of sleep. Nature 1999, 401(6748):36-7.
Sherman RA, Woerman AL, Karstetter KW. Comparative effectiveness of video thermography, contact thermography, and infrared beam thermography for scanning relative skin temperature. J. Rehabil. Res. Dev, 1996; 33(4): 377-86.
INFRARED THERMAL IMAGING AS A MEASURE OF PERIPHERAL TEMPERATURE CHANGE AT SLEEP ONSET: A PILOT STUDY.
Ferguson SA, Gilbert SS, Holmes A, van den Heuvel CJ and Dawson D.
Centre for Sleep Research, University of South Australia, Australia.
Thermoregulation and sleep are interrelated processes. Traditionally, peripheral temperature measurements have been made using contact thermometry. The technique has limitations in that measurements can only be made at discrete points on the body, and from these whole body changes must be inferred. Further, insulation of the area of measurement by the thermistor may itself produce erroneous results. The current study will use digital infrared thermal imaging (DITI) technology to examine the dynamic, whole-body changes in peripheral temperature around the time of sleep onset in real-time. The technology will allow us to assess the normal patterns of heat transfer that occur around the time of sleep onset.
Sixteen healthy male participants, aged 18-30 were recruited to the study. Participants spent an adaptation night and a recording night in the laboratory. We recorded sleep using conventional PSG and temperature using both contact thermometry (core and feet) and DITI (whole upper body). Participants were lying supine in bed with their hands by their sides at least 90 minutes prior to their normal lights out. At the time of lights out they were requested to try and fall asleep in the same position. From 60 minutes prior to lights out thermal images were captured every 30 seconds. Splicing the images together into a continuous animation sequence allowed qualitative assessment of the peripheral temperature changes. Quantitative measurements were taken from regions of interest (hands, forearms, face, neck, chest and torso).
- Infrared thermal images can be captured from participants around the time of sleep onset with minimal loss of data due to movement (fig 1).
- The patterns of heat exchange across the period of sleep onset can be readily visualised in normal sleepers.
- Preliminary data analysis indicates that significant peripheral temperature changes occur in the forearms and hands, in addition to the lower torso region.
Fig 1. Digital infrared thermal images taken from a subject prior to sleep (left panel) and at sleep onset (right panel). The images are grayscaled for better visualisation in black and white. The change in peripheral temperature is most evident in the forearms and hands, and the face and neck, with the darker shade indicating higher temperature.
The results indicate that digital infrared thermal imaging is a technique that can be readily applied to the investigation of sleep initiation processes. Patterns of heat exchange around sleep onset, particularly in the arms and hands, and face and neck can be clearly visualised. Images from the present study will be compared with thermal images collected from sleep-onset insomniacs, with the aim of qualifying the differences in temperature exchange between normal sleepers and insomniacs.