Organ Systems Physiological Changes: Cardiovascular

Vascular changes occur with aging among sedentary volunteers who are considered to be otherwise healthy. The large elastic arteries exhibit an increase in wall thickness and become dilated. Age-associated changes within the vessel media (middle muscular layer of the artery wall), which account for the increase in the diameter of conduit arteries, result from many factors including a relative decrease of elastin (a structural protein with elastic properties) and an increase of collagen (a rigid structural protein). Many chemical properties of elastin deteriorate and the elastin fibers become frayed, resulting in an increased stiffness of the arteries.

With advancing age, the increased pulse-wave velocity, due to increased arterial stiffness, causes pulse-wave reflections from distal arterial branch points to arrive back at the origin of the large arteries prior to closure of the aortic valve, imparting a late augmentation of the systolic pressure and the pulse pressure (the difference between systolic and diastolic pressures). The diastolic pressure amplification due to the normal occurrence of the reflected waves in diastole is reduced in older individuals, and this is associated with a poorer prognosis for patients with cardiovascular diseases.

As a result of arterial stiffening and early reflected pulse waves, the average systolic blood pressure within a healthy, normotensive population increases (within the normal range) with aging, whether measured in a cross-sectional study design or longitudinally. Many individuals show little or no longitudinal increase in systolic pressure, and age-associated increases in blood pressure are therefore neither universal nor inevitable. The average increase in diastolic pressure with aging is modest and is not as marked as the average increase in systolic pressure. An increase in peripheral vascular resistance (PVR; opposition to flow) accompanies aging in some, but not all, individuals, and may be secondary to a reduction in skeletal muscle mass with aging and its a concomitant reduction in capillary density. In healthy men PVR, measured at rest, increases minimally with aging, and it increases moderately in women.