Relation Between Blood Pressure Estimated by Pulse Wave Velocity and Directly Measured Arterial Pressure
Tsukasa Inajima, Yasushi Imai, Masaki Shuzo,
Guillaume Lopez, Shintaro Yanagimoto, Katsuya Iijima,
Hiroyuki Morita, Ryozo Nagai, Naoki Yahagi,
and Ichiro Yamada
The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8655, Japan
Hypertension is the strongest risk factor in cardiac and cerebrovascular diseases among the Japanese. Even daily variations in blood pressure may become a risk, and repeated blood pressure measurement is recommended. Conventional Ambulatory Blood Pressure Monitoring (ABPM), however,may cause discomfort to examinees because they have to have their arms compressed and carry the monitor itself. The number of ABPMmeasurements is limited to about 1 every 15–30 minutes. We therefore attempted, working with medical and engineering teams, to develop a wearable blood pressure sensor that would place less burden on examinees, be less influenced by physical movement, and be usable for continuous blood pressure measurement. We then examined the clinical practicality of the sensor. We modified the existing Moens-Korteweg blood-pressure equation and developed a new systolic blood pressure calculation system that used electrocardiography and ear-lobe pulse waves because the ear lobe would receive little influence from physical movement. We chose three clinical cases from among intensive care unit subjects. We not only estimated their blood pressure using the systemwe developed but also measured arterial pressure directly with an intravascular catheter to see how estimated blood pressure followed actual changes in blood pressure and to evaluate the accuracy of estimated blood pressure. When systolic blood pressure estimated by using the pulse wave velocity method was compared with direct blood pressure measurement, we found that the method captured trends in blood pressure variations correctly. The difference was within ±10 mmHgfor all of the cases. In a comparison using the Bland-Altman method for the three clinical cases, the average difference was –0.4 mmHg, –1.0 mmHg, and –1.7 mmHg and standard deviation was 4.2 mmHg, 4.8 mmHg, and 4.3 mmHg, respectively, which indicated good agreement. Introducing such wearable blood pressure sensors into daily medical practice gets detailed information on continuous blood pressure variation while examinees move freely and the resulting information is used for better quality control of adult diseases. It is also expected that wearable blood pressure sensors can be used in emergency medical cases, in intensive care, and at remote sites.
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