2 Pulse Wave Analysis

Cardiovascular refers to the Cardio (heart) and vascular (blood vessels). The system has two major functional parts: central circulation system and systemic circulation system. Central circulation includes the pulmonary circulation and the heart from where the pulse wave is generated. Systemic circulation is the path that the blood goes from and to the heart. (Green 1984) Pulse wave is detected at arteries which include elastic arteries, medium muscular arteries, small arteries and arterioles. The typical muscular artery has three layers: tunica intima as inner layer, tunica media as middle layer, and tunica adventitia for the outer layer. (Kangasniemi & Opas 1997) The material properties of arteries are highly nonlinear. (langewouters et al. 1984) It depends on the contents of arterial wall: how collagen, elastin and protein are located in the arteries. Functional and structural changes in the arterial wall can be used as early marker for the hypertensive and cardiac diseases. Blood flow is the key to monitor the cardiovascular health condition since it is generated and restrict within such system. Currently the most widely used method for haemodynamic parameters detecting is invasive thermo-dilution method. Impedance-cardiography is the most commonly used non-invasive method nowadays; however, it is too complex for clinical routine check. Pulse wave analysis is an innovative method in the market to do fast and no burden testing (Zhang et al. 2008) Pulse is one of the most critical signals of human life. It comes directly from heart to the blood vessel system. As pulse transmitted, reflections will occur at different level of blood vessels. Other conditions such as resistance of blood flow, elastic of vessel wall, and blood viscosity have clear influence on pulse. Pathological changes affect pulse in different ways: the strength, reflection, and frequency. So pulse provides abundant and reliable information about cardiovascular system. Pulse can be recorded to a set of time series data and represented as a diagraph which is called pulse waveform or pulse wave for short. Gathering pulse at wrist by finger has been a major diagnosis method in China since 500 BC. Physicians used palpation of the pulse as a diagnostic tool during the examination. In 300AD, “Maijing” categoried pulse into 24 types and became the first systematic literature about the pulse. Grecian started to notice the rhythm, strength, and velocity at 400BC. Struthius described a method to watch the pulse wave by putting a leaf on the artery, which is considered as early stage of pulse wave monitoring. In 1860, Etienne Jules Mary invented a level based sphygmograph to measure the pulse rate. It is the first device can actually record the pulse wave. Frederick observed normal radial pressure wave and the carotid