sechenovSechenov Medical JournalСеченовский вестник2218-73322658-3348Сеченовский Университет10.47093/2218-7332.2021.12.1.39-49sechenov-212Research ArticleINTERNAL MEDICINEВНУТРЕННИЕ БОЛЕЗНИComparison of cuffless blood pressure measurement using an electrocardiogram monitor with photoplethysmography function with measurement by the Korotkov method: a pilot studyСравнение безманжетного измерения артериального давления с помощью монитора электрокардиограммы с функцией фотоплетизмографии с измерением по методу Короткова: пилотное исследованиеhttps://orcid.org/0000-0003-0243-6724ГогиберидзеН. А.GogiberidzeN. A.

Гогиберидзе Нана Автандиловна, ассистент кафедры кардиологии, функциональной и ультразвуковой диагностики

ул. Трубецкая, д. 8, стр. 2, г. Москва, 119991

Nana A. Gogiberidze, Assistant Professor, Department of Cardiology, Functional and Ultrasound Diagnostics

8/2, Trubetskaya str., Moscow, 119991

nana10.11@mail.ruhttps://orcid.org/0000-0002-7795-4617СагироваЖ. Н.SagirovaZ. N.

Сагирова Жанна Насибуллаевна, аспирант кафедры кардиологии, функциональной и ультразвуковой диагностики

ул. Трубецкая, д. 8, стр. 2, г. Москва, 119991

Zhanna N. Sagirova, Postgraduate Student, Department of Cardiology, Functional and Ultrasound Diagnostics

8/2, Trubetskaya str., Moscow, 119991

+7 (965) 214-87-77

zhanna.s.n@mail.ruhttps://orcid.org/0000-0003-4717-1272КузнецоваН. О.KuznetsovaN. O.

Кузнецова Наталья Олеговна, аспирант кафедры кардиологии, функциональной и ультразвуковой диагностики

ул. Трубецкая, д. 8, стр. 2, г. Москва, 119991

Natalia O. Kuznetsova, Postgraduate Student, Department of Cardiology, Functional and Ultrasound Diagnostics

8/2, Trubetskaya str., Moscow, 119991

tusia.13@bk.ruhttps://orcid.org/0000-0002-0451-2009ГогниеваД. Г.GognievaD. G.

Гогниева Дарья Геннадиевна, ассистент кафедры кардиологии, функциональной и ультразвуковой диагностики

ул. Трубецкая, д. 8, стр. 2, г. Москва, 119991

Daria G. Gognieva, Assistant Professor, Department of Cardiology, Functional and Ultrasound Diagnostics

8/2, Trubetskaya str., Moscow, 119991

dashkagog@mail.ruhttps://orcid.org/0000-0003-1485-6072ЧомахидзеП. Ш.ChomakhidzeP. Sh.

Чомахидзе Петр Шалвович, д-р мед. наук, профессор кафедры кардиологии, функциональной и ультразвуковой диагностики

ул. Трубецкая, д. 8, стр. 2, г. Москва, 119991

Petr Sh. Chomakhidze, Dr. of Sci. (Medicine), Professor, Department of Cardiology, Functional and Ultrasound Diagnostics

8/2, Trubetskaya str., Moscow, 119991

Petr7747@gmail.comhttps://orcid.org/0000-0002-8025-7433СанерХ.SanerH.

Хьюго Санер, д-р мед. наук, научный сотрудник Центра исследований в области биомедицинской инженерии; консультант

50, Берн, 3008; 18, Берн, 3010

Hugo Saner, Dr. of Sci. (Medicine), Research Associate ARTORG Center for Biomedical Engineering Research; Senior Consultant

50, Murtenstrasse, Bern, 3008; 18, Freiburgstrasse, Bern, 3010

Hugo.Saner@insel.chhttps://orcid.org/0000-0001-5124-6383КопыловФ. Ю.KopylovP. Yu.

Копылов Филипп Юрьевич, д-р мед. наук, профессор кафедры кардиологии, функциональной и ультразвуковой диагностики

ул. Трубецкая, д. 8, стр. 2, г. Москва, 119991

Philipp Yu. Kopylov, Dr. of Sci. (Medicine), Professor, Department of Cardiology, Functional and Ultrasound Diagnostics

8/2, Trubetskaya str., Moscow, 119991

fjk@inbox.ruФГАОУ ВО «Первый Московский государственный медицинский университет им. И.М. Сеченова» Минздрава России (Сеченовский Университет)РоссияSechenov First Moscow State Medical University (Sechenov University)Russian FederationЦентр исследований в области биомедицинской инженерии ARTORG, Бернский университет Муртенштрассе; Университетская клиника кардиологии, Университетский госпиталь Инзельшпиталь ФрайбургштрассеШвейцарияARTORG Center for Biomedical Engineering Research, University of Bern; University Clinic for Cardiology, University Hospital InselspitalSwitzerland2021290420211213949Copyright © Gogiberidze N.A., Sagirova Z.N., Kuznetsova N.O., Gognieva D.G., Chomakhidze P.S., Saner H., Kopylov P.Y., 20212021Гогиберидзе Н.А., Сагирова Ж.Н., Кузнецова Н.О., Гогниева Д.Г., Чомахидзе П.Ш., Санер Х., Копылов Ф.Ю.Gogiberidze N.A., Sagirova Z.N., Kuznetsova N.O., Gognieva D.G., Chomakhidze P.S., Saner H., Kopylov P.Y.Данная работа распространяется под лицензией Creative Commons Attribution 4.0.This work is licensed under a Creative Commons Attribution 4.0 License.https://www.sechenovmedj.com/jour/article/view/212The aim

The aim. To evaluate the reliability of blood pressure (BP) measurement results using a cuffless blood pressure device (CardioQVARK®) in comparison with the values obtained using the Korotkov method.

Materials and methods

Materials and methods. An observational cross-sectional study of 50 patients (25 men, mean age 60 ± 14 years) with arterial hypertension was performed. Blood pressure was measured by the Korotkov method as a standard method, and a CardioQVARK® device, made in the form of a smartphone case, was used as a new method. The device records the electrocardiogram and the photoplethysmogram. Based on the parameters of the electrocardiogram and the photoplethysmogram the systolic and diastolic blood pressure (SBP and DBP) is calculated. Correlation analysis, Student’s t-test, Bland-Altman method were used for comparing the two methods, the standard deviation of the difference and a 95% confidence interval (95% CI) were calculated.

Results

Results. There were no statistically significant differences in the mean values of SBP and DBP for the two methods. There was a strong direct relationship between SBP (r = 0.976, p < 0.0001) and DBP (r = 0.817, p < 0.0001), measured by two methods. Bias for SBP and DBP measured by the new method was: –0.5 mm Hg (95% CI: –1.7; 0.7) and –0.3 mmHg (95% CI: –1.4; 0.7), respectively. The difference in DBP measurements depended on the blood pressure level (r = 0.302, p = 0.03). The underestimation of DBP values was more pronounced for low blood pressure from 55 to 75 mm Hg. At the time of the study, 13 (26%) patients had an increase in blood pressure. The sensitivity of the new method in detecting arterial hypertension was 77% (95% CI: 46; 95), specificity 100% (95% CI: 91; 100), accuracy 94% (95% CI: 83; 99).

Conclusion

Conclusion. The blood pressure measurement method based on the analysis of the electrocardiogram and photoplethysmogram showed reliable blood pressure measurement results in comparison with the Korotkov method.

Цель

Цель: оценить корреляцию между результатами измерений артериального давления с использованием обычного сфигмоманометра с манжетой и результатами портативного монитора электрокардиограммы с функцией фотоплетизмографии.

Материал и методы

Материал и методы: В исследование были включены 50 пациентов в возрасте от 33 до 85 лет (средний возраст 63 года), страдающих артериальной гипертензией. Каждому участнику исследования выполнялось 3 измерения артериального давления с использованием сфигмоманометра с подходящей по размеру манжетой и высчитывалось среднее значение. Затем не более чем через одну минуту после последнего измерения проводилась 3-х минутная запись электрокардиограммы и фотоплетизмограммы с помощью одноканального монитора электрокардиограммы CardioQVARK®, выполненного в виде чехла для смартфона. Значения систолического и диастолического артериального давления рассчитывались с использованием комбинации кардиосигнала и фотоплетизмограммы с помощью специально разработанного алгоритма, основанного на машинном обучении. В дальнейшем данные сравнивались со значениями, полученными при использовании сфигмоманометра.

Результаты

Результаты: Всего было обследовано 55 пациентов и было получено 100 измерений артериального давления от 50 пациентов (5 пациентов по разным причинам были исключены из исследования). По данным анализа Бланда-Альтмана стандартное отклонение для систолического артериального давления составило 4,19, стандартная ошибка среднего – 0,59, Bias= - 0,428. Для диастолического артериального давления стандартное отклонение составило 3,59, стандартная ошибка среднего – 0,51, Bias= - 0,38. Корреляция между показателями сфигмоманометра и монитора CardioQVARK® была равна 0,98(p=0,02) для систолического и 0,88 (p=0,01) для диастолического артериального давления.

Выводы

Выводы: Безманжетное измерение артериального давления с помощью монитора электрокардиограммы с функцией фотоплетизмографии может применяться у большинства пациентов и обеспечивает надежные результаты с минимальными отличиями от значений, полученных с использованием сфигмоманометра с манжетой. Необходимо проведение дальнейших исследований с большим количеством пациентов для изучения потенциала применения метода в клинической практике.

фотоплетизмографияанализ пульсовой волныартериальное давлениеизмерение артериального давленияпортативный монитор электрокардиограммы и фотоплетизмограммысмартфонCardioQVARK®телемедицинаphotoplethysmographypulse wave analysisblood pressureblood pressure measurementportable ECG and PPG monitorsmartphoneCardioQVARKtelemedicineReferencesWhelton P.K., Carey R.M. The 2017 Clinical Practice Guideline for High Blood Pressure. JAMA. 2017; 318(21): 2073–2074. https://doi.org/10.1001/jama.2017.18209 PMID: 29159375Список литературы:McEniery C.M., Cockcroft J.R., Roman M.J., et al. Central blood pressure: current evidence and clinical importance. Eur Heart J. 2014; 35(26): 1719–1725. https://doi.org/10.1093/eurheartj/eht565 PMID: 24459197Whelton P.K., Carey R.M. The 2017 Clinical Practice Guideline for High Blood Pressure. JAMA 2017; 318(21): 2073-74. https://doi.org/10.1001/ jama.2017.18209Van Montfrans G.A. Oscillometric blood pressure measurement: progress and problems. Blood Pressure Monitoring. 2001; 6(6): 287–290. https://doi.org/10.1097/00126097-200112000-00004 PMID: 12055403McEniery C.M., Cockcroft J.R., et al. Central blood pressure: current evidence and clinical importance. Eur Heart J. 2014; 35(26):1719–25. https://doi.org/10.1093/eurheartj/eht565Zheng D., Di Marco L.Y., Murray A. Effect of respiration on Korotkoff sounds and oscillometric cuff pressure pulses during blood pressure measurement. Med Biol Eng Comput. 2014; 52(5): 467–473. https://doi.org/10.1007/s11517-014-1150-1 PMID: 24668326Xing X., Sun M. Optical blood pressure estimation with photoplethysmography and FFT-based neural networks. Biomed Opt Express 2016; 7(8): 3007-20. https://doi.org/10.1364/BOE.7.003007.Xing X., Sun M. Optical blood pressure estimation with photoplethysmography and FFT-based neural networks. Biomed Opt Express 2016; 7(8): 3007–3020. https://doi.org/10.1364/BOE.7.003007 PMID: 27570693Gesche H., Grosskurth D., Kchler G. et al. Continuous blood pressure measurement by using the pulse transit time: comparison to a cuff-based method. European Journal Application Physiology 2012; 112(1): 309-15. https://doi.org/10.1007/s00421-011-1983-3.Yoon Y., Cho J.H., Yoon G. Non-constrained blood pressure monitoring using ECG and PPG for personal Healthcare. J Med Syst. 2009; 33(4): 261–266. https://doi.org/10.1007/s10916-008-9186-0 PMID: 19697692Yoon Y., Cho J.H. and Yoon G. Non-constrained blood pressure monitoring using ECG and PPG for personal Healthcare. J Med Syst. 2009; 33(4): 261-6. https://doi.org/10.1007/s10916-008-9186-0Lin W.H., Wang H., Samuel O.W., et al. New photoplethysmogram indicators for improving cuffless and continuous blood pressure estimation accuracy. Physiol. Meas. 2018; 39(2): 025005. https://doi.org/10.1088/1361-6579/aaa454 PMID: 29319536Poon CCY, Zhang YT. Cuff-less and noninvasive measurements of arterial blood pressure by pulse transit time. Conf Proc IEEE Eng Med Biol Soc (2005) 2005:5877-80. doi: 10.1109/IEMBS.2005.1615827.Ding X.R., Zhang Y.T., Liu J., et al. Continuous cufless blood pressure estimation using pulse transit time and photoplethysmogram intensity ratio. IEEE Trans Biomed Eng. 2016; 63(5): 964–972. https://doi.org/10.1109/TBME.2015.2480679 PMID: 26415147Wong M.Y., Poon C.C., Zhang Y.T. An evaluation of the cuffless blood pressure estimation based on pulse transit time technique: a half year study on normotensive subjects. Cardiovasc Eng 2009; 9(1): 32–38. https://doi.org/10.1007/s10558-009-9070-7.Gao M., Olivier N.B., Mukkamala R. Comparison of noninvasive pulse transit time estimates as markers of blood pressure using invasive pulse transit time measurements as a reference. Physiological Rep. 2016; 4(10): e12768. https://doi.org/10.14814/phy2.12768 PMID: 27233300Lin W.H, Wang H, et al. New photoplethysmogram indicators for improving cuffless and continuous blood pressure estimation accuracy. Physiol. Meas. 2018; 39(2): 025005. https://doi.org/10.1088/1361-6579/aaa454.Tang Z., Sekine M., Tamura T., et al. A chair for cuffless real-time estimation of systolic blood pressure based on pulse transit time. Annu Int Conf IEEE Eng Med Biol Soc. 2015; 2015: 5118–5121. https://doi.org/10.1109/EMBC.2015.7319543 PMID: 26737443Ding X.R., Zhang, et al. Continuous cufless blood pressure estimation using pulse transit time and photoplethysmogram intensity ratio. IEEE Trans. Biomed. Eng. 2016; 63(5): 964–972. https://doi.org/10.1109/TBME.2015.2480679.Mukkamala R., Hahn J.O., Inan O.T., et al. Toward ubiquitous blood pressure monitoring via pulse transit time: theory and practice. IEEE Trans Biomed Eng. 2015; 62(8):1879–1901. https://doi.org/10.1109/TBME.2015.2441951 PMID: 26057530Naschitz J.E., et al. Pulse transit time by R-wave-gated infrared photoplethysmography: review of the literature and personal experience. Journal of Clinical Monitoring and Computing 2004; 18(5-6): 333–342. https://doi.org/10.1007/s10877-005-4300-zFukushima H., Kawanaka H., Bhuiyan M.S., Oguri K. Cuffless blood pressure estimation using only photoplethysmography based on cardiovascular parameters. Annu Int Conf IEEE Eng Med Biol Soc. 2013; 2013: 2132–2135. https://doi.org/10.1109/EMBC.2013.6609955 PMID: 24110142Gao M., et al. Comparison of noninvasive pulse transit time estimates as markers of blood pressure using invasive pulse transit time measurements as a reference. Physiological Reports. (2016) 4(10): 1-10. https://doi.org/10.14814/phy2.12768Shimazaki S., Bhuiyan S., Kawanaka H., Oguri K. Features extraction for cuffless blood pressure estimation by autoencoder from photoplethysmography. Annu Int Conf IEEE Eng Med Biol Soc. 2018 Jul; 2018: 2857–2860. https://doi.org/10.1109/EMBC.2018.8512829 PMID: 30440997Tang Z, et al. A chair for cuffless real-time estimation of systolic blood pressure based on pulse transit time. Conf Proc IEEE Eng Med Biol Soc. (2015) 5118-21. doi: 10.1109/EMBC.2015.7319543.Williams B., Mancia G., Spiering W., et al. 2018 ESC/ESH Guidelines for the management of arterial hypertension: The Task Force for the management of arterial hypertension of the European Society of Cardiology (ESC) and the European Society of Hypertension (ESH). Eur Heart J. 2018; 39(33): 3021–3104. https://doi.org/10.1093/eurheartj/ehy339 PMID: 30165516Y. Yoon, J. H. Cho, and G. Yoon. Non-constrained blood pressure monitoring using ECG and PPG for personal healthcare. Journal of medical systems 2009; 33(4): 261–266. https://doi.org/10.1007/s10916-008-9186-0.Whitworth J.A., World Health Organization, International Society of Hypertension Writing Group. 2003 World Health Organization (WHO)/International Society of Hypertension (ISH) statement on management of hypertension. J Hypertens. 2003; 21(11):1983–1992. https://doi.org/10.1097/00004872-200311000-00002 PMID: 14597836Foo JY, et al. Pulse transit time as an indirect marker for variations in cardiovascular related reactivity. Technol Health Care 2006; 14(2): 97-108.Peng X., Schultz M.G., Picone D.S., et al. Non-invasive measurement of reservoir pressure parameters from brachial-cuff blood pressure waveforms. J Clin Hypertens (Greenwich) 2018; 20(12): 1703–1711. https://doi.org/10.1111/jch.13411 PMID: 30450732Mukkamala, R., J. Hahn, et al. Toward ubiquitous blood pressure monitoring via pulse transit time: theory and practice. IEEE Trans. Biomed. Eng. 2015; 62(8):1879–1901. https://doi.org/10.1109/TBME.2015.2441951.Matsumura K., Rolfe P., Toda S., Yamakoshi T. Cuffless blood pressure estimation using only a smartphone. Sci Rep. 2018; 8(1): 7298. https://doi.org/10.1038/s41598-018-25681-5 PMID: 29740088Shahrbabaki SS, et al. Photoplethysmography derivatives and pulse transit time in overnight blood pressure monitoring. Conf Proc IEEE Eng Med Biol Soc. (2016) 2016: 2855-2858. doi: 10.1109/EMBC.2016.7591325.Krisai P., Vischer A.S., Kilian L., et al. Accuracy of 24-hour ambulatory blood pressure monitoring by a novel cuffless device in clinical practice. Heart. 2019; 105(5): 399–405. https://doi.org/10.1136/heartjnl-2018-313592 PMID: 30228251Fukushima H, et al. Cuffless blood pressure estimation using only photoplethysmography based on cardiovascular parameters. 35th Annual International Conference of the IEEE EMBS. (2013) 2013: 2132-2135. doi: 10.1109/EMBC.2013.6609955Islam S.M.S., Cartledge S., Karmakar C., et al. Validation and acceptability of a cuffless wrist-worn wearable blood pressure monitoring device among users and health care professionals: mixed methods study. JMIR Mhealth Uhealth. 2019; 7(10): e14706. https://doi.org/10.2196/14706 PMID: 31628788Shimazaki S, et al. Features extraction for cuffless blood pressure estimation by autoencoder from photoplethysmography. Conf Proc IEEE Eng Med Biol Soc. (2018) 2018: 2857-2860. doi: 10.1109/EMBC.2018.8512829Liu Z.D., Liu J.K., Wen B., et al. Cuffless blood pressure estimation using pressure pulse wave signals. Sensors. 2018; 18(12): 4227. https://doi.org/10.3390/s18124227 PMID: 30513838Li Y., Wang Z., Lin Z., Yang X.,Song J. Characters available in photoplethysmogram for blood pressure estimation: beyond the pulse transit time. Australas Phys Eng Sci Med 2014; 37(2): 367-76. doi: 10.1007/s13246-014-0269-6.Bard D.M., Joseph J.I., van Helmond N. Cuff-Less methods for blood pressure telemonitoring. Front Cardiovasc Med. 2019; 6: 40. https://doi.org/10.3389/fcvm.2019.00040 PMID: 31157236Miao F., Fu N., Zhang, Y.T., et al. Novel Continuous Blood Pressure Estimation Approach Based on Data Mining Techniques. IEEE J. Biomed. Health Inform. 2017; 21(6): 1730–1740. doi: 10.1109/JBHI.2017.2691715.Khalid S.G., Zhang J., Chen F., Zheng D. Blood pressure estimation using photoplethysmography only: comparison between different machine learning approaches. J Healthc Eng. 2018 Oct 23; 2018: 1548647. https://doi.org/10.1155/2018/1548647 PMID: 30425819Williams B., Mancia G., et al. 2018 ESC/ESH Guidelines for the management of arterial hypertension: The Task Force for the management of arterial hypertension of the European Society of Cardiology (ESC) and the European Society of Hypertension (ESH). European Heart Journal 2018; 39(33): 3021–3104. https://doi.org/10.1093/eurheartj/ehy339Eom H., Lee D., Han S., et al. End-to-End deep learning architecture for continuous blood pressure estimation using attention mechanism. Sensors. 2020; 20(8): 2338. https://doi.org/10.3390/s20082338 PMID: 32325970World Health Organization, International Society of Hypertension Writing Group. 2003 World Health Organization (WHO)/International Society of Hypertension (ISH) statement on the management of hypertension. J Hypertens (2003) 21(11):1983–1992. https://doi.org/10.1097/00004872-200311000-00002.Liu Z., Miao F. Wang R., et al. Cuff-less blood pressure measurement based on deep convolutional neural network. Annu Int Conf IEEE Eng Med Biol Soc. 2019 Jul; 2019: 3775–3778. https://doi.org/10.1109/EMBC.2019.8856588 PMID: 31946696Peng X., Schultz M.G., Picone D.S., Dwyer N., Black J.A., Roberts-Thomson P., Sharman J.E. Non-invasive measurement of reservoir pressure parameters from brachial-cuff blood pressure waveforms. J Clin Hypertens (Greenwich) 2018; 20(12): 1703-1711. https://doi.org/10.1111/jch.13411. Epub 2018 Nov 19.Liu Z.-D., Liu J.-K., Wen B., He Q.-Y., Li Y. and Miao F. Cuffless Blood Pressure Estimation Using Pressure Pulse Wave Signals. Sensors 2018; 18(12): 4227. https://doi.org/10.3390/s18124227Liu Z.-D., Liu J.-K., Wen B., He Q.-Y., Li Y. and Miao F. Cuffless Blood Pressure Estimation Using Pressure Pulse Wave Signals. Sensors 2018; 18(12): 4227. https://doi.org/10.3390/s18124227Eom H., Lee D., Han S., Lim Y, et al. End-to-End deep learning architecture for continuous blood pressure estimation using attention mechanism Sensors 2020; 20(8): 2338. https://doi.org/10.3390/s20082338.Eom H., Lee D., Han S., Lim Y, et al. End-to-End deep learning architecture for continuous blood pressure estimation using attention mechanism Sensors 2020; 20(8): 2338. https://doi.org/10.3390/s20082338.Liu Z, Miao F, Wang R, Liu J, Wen B and Li Y. Cuff-less Blood Pressure Measurement Based on Deep Convolutional Neural Network. Conf Proc IEEE Eng Med Biol Soc. (2019) 2019: 3775-3778. doi: 10.1109/EMBC.2019.8856588.Liu Z, Miao F, Wang R, Liu J, Wen B and Li Y. Cuff-less Blood Pressure Measurement Based on Deep Convolutional Neural Network. Conf Proc IEEE Eng Med Biol Soc. (2019) 2019: 3775-3778. doi: 10.1109/EMBC.2019.8856588.Kaufmann T., Cox E.GM, Wiersema R., Hiemstra B., Eck R.J, Koster G., Scheeren T.WL, Keus F., Saugel B. Non-invasive oscillometric versus invasive arterial blood pressure measurements in critically ill patients: A post hoc analysis of a prospective observational study. J Crit Care 2020; 57: 118-123. https://doi.org/10.1016/j.jcrc.2020.02.013.Kaufmann T., Cox E.GM, Wiersema R., Hiemstra B., Eck R.J, Koster G., Scheeren T.WL, Keus F., Saugel B. Non-invasive oscillometric versus invasive arterial blood pressure measurements in critically ill patients: A post hoc analysis of a prospective observational study. J Crit Care 2020; 57: 118-123. https://doi.org/10.1016/j.jcrc.2020.02.013.Khalid S.G., Zhang J., Chen F. and Zheng D. Blood Pressure Estimation Using Photoplethysmography Only: Comparison between Different Machine Learning Approaches. Journal of Healthcare Engineering 2018; 2018:1548647. https://doi.org/10.1155/2018/1548647Khalid S.G., Zhang J., Chen F. and Zheng D. Blood Pressure Estimation Using Photoplethysmography Only: Comparison between Different Machine Learning Approaches. Journal of Healthcare Engineering 2018; 2018:1548647. https://doi.org/10.1155/2018/1548647Matsumura K, Rolfe P, Toda S and Yamakoshi T. (2018). Cuffless blood pressure estimation using only a smartphone. SCIEnTIFIC Reports 2018; 8(1): 7298. https://doi.org/10.1038/s41598-018-25681-5Matsumura K, Rolfe P, Toda S and Yamakoshi T. (2018). Cuffless blood pressure estimation using only a smartphone. SCIEnTIFIC Reports 2018; 8(1): 7298. https://doi.org/10.1038/s41598-018-25681-5Bard DM, Joseph JI and van Helmond N (2019) Cuff-Less Methods for Blood Pressure Telemonitoring. Front. Cardiovasc. Med. 6:40. https://doi.org/10.3389/fcvm.2019.00040.Bard DM, Joseph JI and van Helmond N (2019) Cuff-Less Methods for Blood Pressure Telemonitoring. Front. Cardiovasc. Med. 6:40. https://doi.org/10.3389/fcvm.2019.00040.

The authors declare that there are no conflicts of interest present.