Uncontrolled hypertension or high blood pressure (BP) was a major risk factor that links to potential development of serious diseases such as stroke, hypertensive heart disease, and coronary artery disease. BP was influenced by many factors such as food, exercise, mental situations, stress, among others; thus, it varied considerably from time to time. Instantaneous information about BP status could be obtained from conventional standard cuff-based BP measurement, such as oscillometry and auscultation. However, these methods were not applicable to ambulatory BP monitoring (ABPM) or home BP monitoring (HBPM) due to the cumbersome and discontinue nature of cuff wrapping around the arm or leg to detect the oscillations during cuff-deflation and the limited frequency of measurement. Moreover, the clinical BP which may not reflect the normal level due to the effect of white coat effect had been questioned. Therefore, the development of cuff-less BP monitoring technology was extremely urgent.
