Influence of arterial pulse and reflective waves on systolic blood pressure and cardiac function.

Hypertension is a cardiovascular risk factor classically attributed to a reduction in the calibre and/or number of small arteries and arterioles resulting in increased peripheral vascular resistance. The definition of blood pressure as a product of total peripheral resistance (TPR) and cardiac output, however, does not take into account the fluctuation of blood pressure and flow during the cardiac cycle, with systolic and diastolic blood pressure representing the extremes of pulse pressure fluctuations. Diastolic blood pressure is closer to mean blood pressure (and therefore to TPR) than systolic blood pressure, and as such has been used as a marker for the diagnosis of hypertension. However, this approach has no rational basis and was challenged by the Framingham Heart Study which demonstrated that systolic rather than diastolic blood pressure is a better risk marker for stroke and coronary artery disease in subjects aged 45 years and older. This view has subsequently been confirmed by several epidemiological and interventional studies. Systolic blood pressure is closely associated with pulse pressure and is determined by the pattern of left ventricular ejection, arterial stiffness and timing of arterial wave reflections, i.e. the geometrical and viscoelastic properties of large conduit arteries. In humans, with ageing and hypertension, the arteries stiffen as a result of progressive degeneration of the arterial media, increased collagen and calcium content, and dilation and hypertrophy of large arteries and the aorta. Thus, the increase in systolic blood pressure (as a result of arterial damage) increases the fatigue of arterial walls and accelerates arterial damage, producing a self-perpetuating cycle.