Oscillometric blood pressure measurement using a ring
Lindén, Arttu (2020)
2020
Biotekniikan DI-tutkinto-ohjelma - Degree Programme in Bioengineering, MSc (Tech)
Lääketieteen ja terveysteknologian tiedekunta - Faculty of Medicine and Health Technology
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Hyväksymispäivämäärä
2020-06-02
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tuni-202005054946
https://urn.fi/URN:NBN:fi:tuni-202005054946
Tiivistelmä
Cardiovascular diseases are the leading cause of death globally. One of the most important risk factors of cardiovascular diseases is chronically elevated blood pressure or hypertension. Hypertension is not only a health risk but a significant economic burden to the society. For these reasons accurate measurement of blood pressure is important.
Blood pressure is typically measured using oscillometric or auscultatory method in which the brachial artery of the upper arm is occluded using an inflatable cuff. By deflating the cuff, the blood pressure can be measured in the auscultatory method by listening to specific Korotkoff sounds. In the oscillometric method the measurement is based on measuring the amplitude of blood pressure oscillations as the cuff is deflated. The disadvantage of the current methods is that the devices are large and inconvenient to use. Furthermore, the use of the inflatable cuff can feel unpleasant for some patients. Due to the issues related to current devices, there is a continuous demand for more patient friendly technologies.
At Lakka Health we are developing a ring used to noninvasively measure blood pressure from the finger. The ring is based on the oscillometric method. In the ring, the inflatable cuff is replaced with a smart-metal-alloy actuator. The oscillometric blood pressure pulses are detect-ed using a piezo sensor system and the pressure is measured indirectly with a force measurement system. This system is based on sensing the position of a magnet using a magnetometer.
One objective of the thesis was to show how the different technologies used in the arm-cuff devices can be replaced to create a ring that can be used to measure blood pressure from the finger. Another objective was to determine the accuracy of a prototype of the ring by comparing it to a clinically validated arm-cuff device. The comparison study was conducted based on the guidelines given in the validation standard for new automatic sphygmomanometers with a small number of subjects (n = 8).
The results of the comparison study were that the mean value of the differences for diastolic and systolic blood pressure between the reference sphygmomanometer and the ring were +56,8 and +40,1 mmHg with standard deviation of 10,4 and 18,1 mmHg, respectively. Further-more, the diastolic blood pressure had statistically significant moderate correlation (p-value = 0,0066, r = 0,4980, N = 24). Contrarily, the systolic blood pressure did not have statistically significant correlation (p-value = 0,1595, r = 0,2124, N = 24).
Based on the results, it was determined that the ring overestimates both systolic and diastolic blood pressure. Furthermore, the standard deviation of the differences was too high and did not meet the validation requirements. Poor accuracy of the ring was shown to be caused by unreliable force measurement using the magnetometer and magnet. At the end of the thesis, recommendations are given on how to improve the accuracy of the ring by making changes to the force measurement concept.
Blood pressure is typically measured using oscillometric or auscultatory method in which the brachial artery of the upper arm is occluded using an inflatable cuff. By deflating the cuff, the blood pressure can be measured in the auscultatory method by listening to specific Korotkoff sounds. In the oscillometric method the measurement is based on measuring the amplitude of blood pressure oscillations as the cuff is deflated. The disadvantage of the current methods is that the devices are large and inconvenient to use. Furthermore, the use of the inflatable cuff can feel unpleasant for some patients. Due to the issues related to current devices, there is a continuous demand for more patient friendly technologies.
At Lakka Health we are developing a ring used to noninvasively measure blood pressure from the finger. The ring is based on the oscillometric method. In the ring, the inflatable cuff is replaced with a smart-metal-alloy actuator. The oscillometric blood pressure pulses are detect-ed using a piezo sensor system and the pressure is measured indirectly with a force measurement system. This system is based on sensing the position of a magnet using a magnetometer.
One objective of the thesis was to show how the different technologies used in the arm-cuff devices can be replaced to create a ring that can be used to measure blood pressure from the finger. Another objective was to determine the accuracy of a prototype of the ring by comparing it to a clinically validated arm-cuff device. The comparison study was conducted based on the guidelines given in the validation standard for new automatic sphygmomanometers with a small number of subjects (n = 8).
The results of the comparison study were that the mean value of the differences for diastolic and systolic blood pressure between the reference sphygmomanometer and the ring were +56,8 and +40,1 mmHg with standard deviation of 10,4 and 18,1 mmHg, respectively. Further-more, the diastolic blood pressure had statistically significant moderate correlation (p-value = 0,0066, r = 0,4980, N = 24). Contrarily, the systolic blood pressure did not have statistically significant correlation (p-value = 0,1595, r = 0,2124, N = 24).
Based on the results, it was determined that the ring overestimates both systolic and diastolic blood pressure. Furthermore, the standard deviation of the differences was too high and did not meet the validation requirements. Poor accuracy of the ring was shown to be caused by unreliable force measurement using the magnetometer and magnet. At the end of the thesis, recommendations are given on how to improve the accuracy of the ring by making changes to the force measurement concept.