A review on non-invasive hypertension monitoring system by using photoplethysmography method

Abstract

Hypertension, the abnormal elevation of blood pressure, is one of the chronic disease that usually comes with no symptom and signal. As the systolic blood pressure (SBP) over 140 mm Hg or diastolic blood pressure (DBP) is over 90 mmHg, it is considered as hypertension. The purpose of this paper is to determine a method to early diagnose of hypertension by monitoring the SBP, DBP, and heart rate (HR) non-invasively. Although accurate measurement of BP and HR of a person can be obtained invasively, the measuring probe needs to place under patient’s skin and it would cause wound. Therefore, this paper review on methods to measure BP and HR non-invasively. External pressures are needed to induce to the artery in order to measure BP and HR by using auscultatory and oscillometric methods, hence, a pressure cuff is used for measuring BP. The pressure cuff will restrict the motion of patient and it is not suitable for continuous monitoring. Pulse transit time (PTT) and photoplethysmography (PPG) methods are introduced to measuring BP non-invasively without cuff. The limitation of PTT over PPG is PTT needs both PPG waveform and ECG waveform to estimate BP, and artificial phase lag is occurred which will affect the reliability of the measured result. Therefore, for long term monitoring hypertension, non-invasively, by using photoplephymosgraphy method is preferred since it enables continuous monitoring without cuff and it is only one waveform, which is PPG waveform, is needed to estimate the BP as well as HR.