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 diseases that usually comes with no symptom and signal. Hypertension is diagnosed if the systolic blood pressure (SBP) over 140 mm Hg or diastolic blood pressure (DBP) is over 90 mmHg. The purpose of this paper is to review methods of early diagnosis 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, which in turn would cause discomfort to the patients and not to mention the possibility of thrombosis to occur. External pressures are necessary to induce to the artery in order to measure BP and HR by using auscultatory and oscillometric methods, hence, a pressure cuff is used to measure BP. The pressure cuff will restrict the motion of the patient and it is rendered not suitable for continuous monitoring. On the other hand, pulse transit time (PTT) and photoplethysmography (PPG) methods are introduced to measure BP non-invasively without the use of a cuff. The limitation of PTT over PPG is PTT needs both PPG waveform and ECG waveform to estimate BP, and artificial phase lag might occur which will affect the reliability of the measured result. Therefore, for long-term hypertension monitoring, non-invasive mean using photoplethysmography method is preferred since it enables continuous monitoring without cuff and it requires only one waveform to estimate the BP as well as HR.