We Debunk Myths about Temperature and Saturation Measurements Using Wrist Devices

Temperature and saturation measurements obtained from the wrist are burdened with high potential error and low reliability of the collected data.

Simultaneous measurement of temperature and saturation by one wrist device seems to be an extremely convenient solution, but a review of the literature clearly indicates a lack of substantive grounds for performing measurements in this way.

Saturation measurement

Pulse oximetry is a non-invasive method of percutaneous monitoring of oxygen saturation of arterial blood hemoglobin and pulse frequency. For this purpose, devices called pulse oximeters are used, operating on the principle of transmission spectrophotometry, using various optical properties of oxygenated and deoxygenated hemoglobin.

Reliable saturation measurement should be carried out in an appropriate manner:

• In places with sufficient blood flow (fingers, toes or earlobes). PPG sensors are commonly used on fingers due to the high signal amplitude that can be obtained compared to other places.
• At rest – the pulse oximeter is a device very sensitive to movement. Movement in the measuring system causes significant disturbances, as a result of which the calculation of blood oxygen saturation can be false.
• The correct clamping force of the device to the place of measurement [see footnotes 1, 2, 3, 4].
• The amount of light reaching the pulse oximeter detector from the diodes should be much greater than the amount of light coming from the environment.

Blood saturation measurements with a pulse oximeter must therefore meet a number of conditions in order to be interpreted as reliable at the clinical level. To quote Bioengineering Professor Lex Schulthesis, former head of the Center for Radiological Devices and Health at the Food and Drug Administration, “Some currently available devices for home saturation measurement do not meet the standards for medical devices and their effectiveness has not been properly validated”5. Such devices include, among others, wristbands and watches, which have been developed and introduced to the market by several manufacturers. These devices, although easier to wear, are not used in clinical settings due to the currently insurmountable technical problems that saturation measurement in the wrist area presents. As a consequence, a device such as a wristband or watch cannot meet the correct measurement conditions listed above.

Body temperature measurement

Traditionally, body temperature measurement is performed using contact thermometers, requiring direct contact of the device/sensor with the skin or mucous membrane of the subject. The place of measurement must be taken into account. For example, a measurement from the mouth is 0.3-0.5 degrees Celsius higher than a measurement from the armpit.

Recently, devices have also appeared on the market that offer body temperature measurements on the wrist. These are bands or watches. However, there is no scientific basis for measuring the temperature at this location. This way of measuring temperature is not compatible with current medical knowledge (standardized and based on research). Only one-off studies have been conducted on such a method of measurement, and their results are contradictory. For example, a paper published in May 2020 by Hsuan-Yu Chen et al. clearly states that the wrist temperature measurement value shows significant deviations from the temperature of the tympanic membrane (taken as a reference value) and cannot be used to monitor fever.6 One work appears to confirm the hypothesis about the effectiveness of wrist measurements – in fact, temperature measurements were made 10 cm above the wrist (due to the lower impact of ambient temperature on the measurement in this location), i.e., not where a watch or band is typically and constantly worn.7 The temperature of the skin on the wrist and forearm does not correspond to the actual body temperature, and is very susceptible to external factors, such as wearing long-sleeved blouses or being in a cool or warm room.

Summary

Correct temperature and saturation measurement should be carried out by dedicated devices. Inaccuracy of measurements can be acceptable in fitness solutions, but can lead to false conclusions in healthcare, resulting in erroneous decisions made by telecare workers, such as unnecessarily triggering alarm procedures or not running them when necessary.

If you want to know more about this, we encourage you to read our free white paper.

Sources:

1. Understanding Pulse Oximetry: SpO2 Concepts (PDF). Philips Medical Systems. Retrieved 19 August 2016. http://incenter.medical.philips.com/doclib/enc/fetch/586262/586457/Understanding_ Pulse_Oximetry.pdf%3Fnodeid%3D586458%26vernum%3D2
2. https://www.howequipmentworks.com/pulse_oximeter/
3. Wearable Photoplethysmographic Sensors—Past and Present. Toshiyo Tamura, Yuka Maeda, Masaki Sekine, Masaki Yoshida. Electronics volume 3, issue 2, P282-302 2014 DOI: 10.3390/electronics3020282
4. Current progress of photoplethysmography and SPO2 for health monitoring. Toshiyo Tamura. Biomed Eng Lett. 2019 Feb; 9(1): 21–36. doi: 10.1007/s13534-019-00097-w. eCollection 2019 Feb
5. Pulse Oximeter & COVID-19 Shortness of Breath - Consumer Reports
6. Investigation of the Impact of Infrared Sensors on Core Body Temperature Monitoring by Comparing Measurement Sites. Hsuan-Yu Chen 1, Andrew Chen 2, Chiachung Chen 3 Sensors (Basel). 2020 May 19;20(10):2885. doi: 10.3390/s20102885.
7. Validity of Wrist and Forehead Temperature in Temperature Screening in the General Population During the Outbreak of 2019 Novel Coronavirus: a prospective real-world study. Ge Chen, Jiarong Xie, Guangli Dai, Peijun Zheng, Xiaqing Hu, Hongpeng Lu, Lei Xu, Xueqin Chen, Xiaomin Chen. doi: https://doi.org/10.1101/2020.03.02.20030148