Arterial Elastance and Wave Reflection Augmentation of Systolic Blood Pressure: Deleterious Effects and Implications for Therapy

Abstract

Systolic and pulse blood pressures are stronger predictors of stroke, coronary heart disease, myocardial infarction, heart failure, end-stage renal disease, and cardiovascular mortality than diastolic pressure. Furthermore, diastolic pressure is inversely related to coronary heart disease and cardiovascular mortality. Increased elastance (or stiffness, inverse of compliance) of the central elastic arteries is the primary cause of increased systolic and pulse pressure with advancing age and in patients with cardiovascular disease, including hypertension, and is due to degeneration and hyperplasia of the arterial wall; diastolic pressure decreases as arterial elastance increases. As elastance increases, transmission velocity of both forward and backward (or reflected) traveling waves increases, which causes the reflected wave to arrive earlier in the central aorta and augments pressure in late systole. These changes in arterial wall properties cause an increase in left ventricular afterload and myocardial oxygen consumption and a decrease in myocardial perfusion pressure, which may induce an imbalance in the supply-demand ratio, especially in hypertrophied hearts with coronary artery disease. Also, an increase in systolic pressure increases arterial wall circumferential stress, which promotes fatigue and development of atherosclerosis. Vasodilator drugs have little direct active effect on large elastic arteries but can markedly reduce wave reflection amplitude and augmentation index by decreasing elastance of the muscular arteries and reducing pulse wave velocity of the reflected wave from the periphery to the heart. This decrease in intensity (or amplitude) and increase in travel time (or delay) of the reflected wave causes a generalized decrease in systolic pressure and arterial wall stress and an increase in ascending aortic flow during the deceleration phase. The decrease in systolic pressure brought about by this mechanism is grossly underestimated when systolic pressure is measured in the brachial artery.