{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T01:18:58Z","timestamp":1760145538078,"version":"build-2065373602"},"reference-count":24,"publisher":"MDPI AG","issue":"15","license":[{"start":{"date-parts":[[2024,7,27]],"date-time":"2024-07-27T00:00:00Z","timestamp":1722038400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Sleep Number Corporation"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>The transition from wakefulness to sleep occurs when the core body temperature decreases. The latter is facilitated by an increase in the cutaneous blood flow, which dissipates internal heat into the micro-environment surrounding the sleeper\u2019s body. The rise in cutaneous blood flow near sleep onset causes the distal (hands and feet) and proximal (abdomen) temperatures to increase by about 1 \u00b0C and 0.5 \u00b0C, respectively. Characterizing the dynamics of skin temperature changes throughout sleep phases and understanding its relationship with sleep quality requires a means to unobtrusively and longitudinally estimate the skin temperature. Leveraging the data from a temperature sensor strip (TSS) with five individual temperature sensors embedded near the surface of a smart bed\u2019s mattress, we have developed an algorithm to estimate the distal skin temperature with a minute-long temporal resolution. The data from 18 participants who recorded TSS and ground-truth temperature data from sleep during 14 nights at home and 2 nights in a lab were used to develop an algorithm that uses a two-stage regression model (gradient boosted tree followed by a random forest) to estimate the distal skin temperature. A five-fold cross-validation procedure was applied to train and validate the model such that the data from a participant could only be either in the training or validation set but not in both. The algorithm verification was performed with the in-lab data. The algorithm presented in this research can estimate the distal skin temperature at a minute-level resolution, with accuracy characterized by the mean limits of agreement [\u22120.79 to +0.79 \u00b0C] and mean coefficient of determination R2=0.87. This method may enable the unobtrusive, longitudinal and ecologically valid collection of distal skin temperature values during sleep. Therelatively small sample size motivates the need for further validation efforts.<\/jats:p>","DOI":"10.3390\/s24154882","type":"journal-article","created":{"date-parts":[[2024,7,29]],"date-time":"2024-07-29T12:27:43Z","timestamp":1722256063000},"page":"4882","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":3,"title":["Unobtrusive Skin Temperature Estimation on a Smart Bed"],"prefix":"10.3390","volume":"24","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-4621-4667","authenticated-orcid":false,"given":"Gary","family":"Garcia-Molina","sequence":"first","affiliation":[{"name":"Sleep Number Labs, San Jose, CA 95113, USA"},{"name":"Department of Psychiatry, University of Wisconsin, Madison, WI 53719, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Trevor","family":"Winger","sequence":"additional","affiliation":[{"name":"Sleep Number Labs, San Jose, CA 95113, USA"},{"name":"Department of Computer Science and Engineering, University of Minnesota, Minneapolis, MN 55455, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Nikhil","family":"Makaram","sequence":"additional","affiliation":[{"name":"Sleep Number Labs, San Jose, CA 95113, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Megha Rajam","family":"Rao","sequence":"additional","affiliation":[{"name":"Sleep Number Labs, San Jose, CA 95113, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Pavlo","family":"Chernega","sequence":"additional","affiliation":[{"name":"GlobalLogic, 03038 Kyiv, Ukraine"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Yehor","family":"Shcherbakov","sequence":"additional","affiliation":[{"name":"GlobalLogic, 03038 Kyiv, Ukraine"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Leah","family":"McGhee","sequence":"additional","affiliation":[{"name":"Sleep Number Corporation, Minneapolis, MN 55404, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Vidhya","family":"Chellamuthu","sequence":"additional","affiliation":[{"name":"Sleep Number Labs, San Jose, CA 95113, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Erwin","family":"Veneros","sequence":"additional","affiliation":[{"name":"Sleep Number Labs, San Jose, CA 95113, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Raj","family":"Mills","sequence":"additional","affiliation":[{"name":"Sleep Number Corporation, Minneapolis, MN 55404, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Mark","family":"Aloia","sequence":"additional","affiliation":[{"name":"Sleep Number Corporation, Minneapolis, MN 55404, USA"},{"name":"Department of Medicine, National Jewish Health, Denver, CO 80206, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-0822-1732","authenticated-orcid":false,"given":"Kathryn J.","family":"Reid","sequence":"additional","affiliation":[{"name":"Center for Circadian and Sleep Medicine, Department of Neurology, Feinberg School of Medicine, Northwestern University, Chicago, IL 60611, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2024,7,27]]},"reference":[{"key":"ref_1","unstructured":"Someren, E.J.V. (2006). Chapter 18: Mechanisms and Functions of Coupling Between Sleep and Temperature Rhythms, Elsevier."},{"key":"ref_2","doi-asserted-by":"crossref","unstructured":"Zoccoli, G., Silvani, A., and Franzini, C. (2013). Sleep and the Peripheral Vascular System, Elsevier.","DOI":"10.1016\/B978-0-12-378610-4.00113-3"},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"R741","DOI":"10.1152\/ajpregu.2000.278.3.R741","article-title":"Functional link between distal vasodilation and sleep-onset latency?","volume":"278","author":"Krauchi","year":"2000","journal-title":"Am. J. Physiol. Regul. Integr. Comp. Physiol."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"36","DOI":"10.1038\/43366","article-title":"Warm feet promote the rapid onset of sleep","volume":"401","author":"Cajochen","year":"1999","journal-title":"Nature"},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"13","DOI":"10.1186\/s40101-018-0172-z","article-title":"Effects of feet warming using bed socks on sleep quality and thermoregulatory responses in a cool environment","volume":"37","author":"Ko","year":"2018","journal-title":"J. Physiol. Anthropol."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"1589","DOI":"10.1152\/ajpregu.00492.2004","article-title":"Cutaneous warming promotes sleep onset","volume":"288","author":"Raymann","year":"2005","journal-title":"Am. J. Physiol. Regul. Integr. Comp. Physiol."},{"key":"ref_7","doi-asserted-by":"crossref","unstructured":"Siyahjani, F., Molina, G.G., Barr, S., and Mushtaq, F. (2022). Performance Evaluation of a Smart Bed Technology against Polysomnography. Sensors, 22.","DOI":"10.3390\/s22072605"},{"key":"ref_8","unstructured":"Sleep Number Corporation (2024, July 05). Sleep Number\u00ae Climate360\u00ae Smart Bed. Available online: https:\/\/www.sleepnumber.com\/products\/climate360."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"489","DOI":"10.1016\/j.physbeh.2006.04.026","article-title":"Evaluation of wireless determination of skin temperature using iButtons","volume":"88","author":"Daanen","year":"2006","journal-title":"Physiol. Behav."},{"key":"ref_10","doi-asserted-by":"crossref","unstructured":"Mccarthy, C., Pradhan, N., Redpath, C., and Adler, A. (2016, January 29\u201331). Validation of the Empatica E4 Wristband. Proceedings of the 2016 IEEE EMBS International Student Conference (ISC), Ottawa, ON, Canada.","DOI":"10.1109\/EMBSISC.2016.7508621"},{"key":"ref_11","unstructured":"iButton Link (2024, July 08). DS1922L iButton. Available online: https:\/\/www.ibuttonlink.com\/products\/ds1922l."},{"key":"ref_12","unstructured":"Empatica, S.R.L. (2024, July 08). Empatica E4 Tech Specs. Available online: https:\/\/box.empatica.com\/documentation\/20141119_E4_TechSpecs.pdf."},{"key":"ref_13","unstructured":"AASM (2014). International Classification of Sleep Disorders, American Academy of Sleep Medicine. [3rd ed.]."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"A39","DOI":"10.1093\/sleep\/zsac079.084","article-title":"0086 Unobtrusive Sensing of Skin Temperature During Sleep Using a Mattress Sensor","volume":"45","author":"Makaram","year":"2022","journal-title":"Sleep"},{"key":"ref_15","unstructured":"Tartarini, F., and Schiavon, S. (2020, January 1\u20135). Skin Temperature Sampling Period for Longitudinal Thermal Comfort Studies. Proceedings of the 16th International Conference on Indoor Air Quality and Climate (INDOOR AIR 2020), Seoul, Republic of Korea."},{"key":"ref_16","doi-asserted-by":"crossref","unstructured":"Chen, T., and Guestrin, C. (2016, January 13\u201317). Xgboost: A scalable tree boosting system. Proceedings of the 22nd ACM SIGKDD International Conference on Knowledge Discovery and Data Mining, San Francisco, CA, USA.","DOI":"10.1145\/2939672.2939785"},{"key":"ref_17","unstructured":"Breiman, L. (2001). Random Forests, Springer."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"829","DOI":"10.1080\/01621459.1979.10481038","article-title":"Robust Locally Weighted Regression and Smoothing Scatterplots","volume":"74","author":"Cleveland","year":"1979","journal-title":"J. Am. Stat. Assoc."},{"key":"ref_19","unstructured":"Kohavi, R. (1995, January 20\u201325). A Study of Cross-Validation and Bootstrap for Accuracy Estimation and Model Selection. Proceedings of the 1995 International Joint Conference on AI, Montreal, QC, Canada."},{"key":"ref_20","unstructured":"Bergstra, J., Yamins, D., and Cox, D.D. (2013, January 16\u201321). Making a Science of Model Search: Hyperparameter Optimization in Hundreds of Dimensions for Vision Architectures. Proceedings of the 30th International Conference on Machine Learning (ICML 2013), Atlanta, GA, USA."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"307","DOI":"10.1016\/S0140-6736(86)90837-8","article-title":"Statistical methods for assessing agreement between two methods of clinical measurement","volume":"1","author":"Bland","year":"1986","journal-title":"Lancet"},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"e623","DOI":"10.7717\/peerj-cs.623","article-title":"The coefficient of determination R-squared is more informative than SMAPE, MAE, MAPE, MSE and RMSE in regression analysis evaluation","volume":"7","author":"Chicco","year":"2021","journal-title":"PeerJ Comput. Sci."},{"key":"ref_23","doi-asserted-by":"crossref","unstructured":"Aldoseri, A., Al-Khalifa, K.N., and Hamouda, A.M. (2023). Re-Thinking Data Strategy and Integration for Artificial Intelligence: Concepts, Opportunities, and Challenges. Appl. Sci., 13.","DOI":"10.20944\/preprints202305.1565.v2"},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"S92","DOI":"10.1016\/S0893-133X(01)00315-3","article-title":"Circadian clues to sleep onset mechanisms","volume":"25","year":"2001","journal-title":"Neuropsychopharmacology"}],"container-title":["Sensors"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1424-8220\/24\/15\/4882\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,10]],"date-time":"2025-10-10T15:25:04Z","timestamp":1760109904000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1424-8220\/24\/15\/4882"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2024,7,27]]},"references-count":24,"journal-issue":{"issue":"15","published-online":{"date-parts":[[2024,8]]}},"alternative-id":["s24154882"],"URL":"https:\/\/doi.org\/10.3390\/s24154882","relation":{},"ISSN":["1424-8220"],"issn-type":[{"type":"electronic","value":"1424-8220"}],"subject":[],"published":{"date-parts":[[2024,7,27]]}}}