It was an English medical professor—some 400 years ago—who first made that observation about arteries and aging. –some 400 years ago. But it’s never been more true or relevant than now. When it comes to aging, you really can judge people by their arteries.
Everyone knows that the cardiovascular system is a key to being healthy and living long, but most people mistakenly focus on the cardio part—the heart—when it’s the vascular they should be most concerned with. That’s because it’s impossible to have a healthy heart without taking care of the blood vessels. Keep the arteries healthy and the heart will follow suit. This becomes ever more vital the older we get. The greatest risk factor for cardiovascular disease isn’t smoking or being overweight or having high cholesterol. It’s age.
It comes down to this basic fact of human physiology: The walls of our large arteries, particularly the aorta, thicken, stiffen and dilate as we get older. That’s a bad thing for healthy blood flow and increases our risk of heart disease and stroke. So that’s what we measure as a primary biomarker of aging.
Knowing how stiff your arteries are will give you more vital information about how well you are aging than your blood pressure, cholesterol or blood sugar, the basic elements of a typical routine physical.
Even if you had a more thorough workup–an electrocardiogram to screen for irregularities in heart rhythm, or an ultrasound display of heart action called an echocardiogram, or even a stress test to detect hidden abnormalities—your doctor could pronounce you in perfect health by traditional standards without measuring, let alone addressing, the single biggest cause of heart failure and stroke: The unseen stiffening of the large arteries that all normal, healthy adults undergo as they get older.
Arterial stiffness, which has been commonly referred to over the years as arteriosclerosis or “hardening of the arteries,” is a long-established condition associated with aging. But only in recent years have researchers found evidence that it has an important impact beyond the blood vessels themselves. Stiffness of the arteries seems to affect both the heart’s structure and its function. It is the major cause of high blood pressure in older people—and that, in turn, is a leading risk factor for stroke, coronary artery disease, heart attacks, and heart failure. It’s also suspected that stiffer arteries are more prone to accumulate deposits of cholesterol, white blood cells, and clotting factors that make the interior of the artery wall thick and irregular—a precursor to coronary artery disease and stroke.
The question is one of degree, and of individuality, as it is in all aspects of the biomarker approach: How stiff are your arteries—and what trajectory of aging are they on? Taking an accurate measure of that process gives us an invaluable biomarker of aging. And it all starts with the pulse.
The human pulse is a product of the cardiac cycle—the rhythmical filling of the chambers of the heart with blood from the veins, called diastole, and the subsequent ejection of the blood into the arteries, called systole. The cardiac cycle is a marvel of biological engineering that supplies the tissues and organs of your body with blood that carries oxygen and nutrients, and then brings carbon dioxide back to your lungs and metabolic substances to your liver and kidneys for processing and excretion.
The wave of blood traveling through the arterial system has two characteristics that can be measured. A standard blood pressure test yields both systolic and diastolic pressure—systole on top, diastole on the bottom, as in 120/80. The combination of a high number on top and a low number on the bottom indicates an increased risk of cardiovascular disease. So the best indicator is the difference between the two, and this is called pulse pressure (PP).
A device called SphygmoCor goes a step further, assessing what’s called the “reflected wave” of blood flow to measure arterial stiffness. To visualize the concept of the reflected wave, think of what happens when you throw a rock into the middle of a man-made pond. The ripples that emanate from the spot where the stone hits are the forward waves. When those forward waves hit the pond’s stone wall, they send back ripples. These are the reflected waves. Now think of this phenomenon in terms of your heart and the circulatory process of the blood vessels. The speed of the reflected wave is determined by the stiffness of the arteries along which they travel. The stiffer the arteries, the more quickly the wave travels out and the earlier the reflected wave arrives back at the heart.
This is the fundamental factor behind the question of whether your arteries—and, hence, your entire cardiovascular system—are young at heart or they’re old for their age. In a young and healthy person, the aorta and central arteries are quite elastic and expand to accept blood flow without much of an increase in pressure. The peripheral arteries, meanwhile, dilate and constrict with ease. Unfortunately, supple arteries don’t last forever. In fact, the larger elastic arteries begin to stiffen as early as one’s twenties, a process that continues until the aorta of many an 80-year-old finally becomes a rigid tube.
The collision of the forward and reflected waves causes an increase in central pressure in the aorta (but not in the arm, where simple blood pressure is measured). This is called the augmentation pressure (AP). This number is a function of both the speed of the reflected wave and how much resistance the forward wave meets when it hits the smaller vessels. So the AP combines the two major facets of arterial aging—stiffening of the large arteries and constriction of the resistance arteries in a single measurement that increases with age.
The SphygmoCor device uses a highly sensitive pressure probe to record the shape of the arterial pulse wave at the wrist. The instrument’s software then analyzes the pressure wave to compute the augmentation pressure in the aorta as it comes off the heart.
A computer program developed for PhysioAge then compares the number with those of more than 4,000 healthy men and women in our database to yield the person’s CardioAge. If that person is 50, does he have the cardiovascular system typically seen in someone older, younger or about the same age?
The results can then inform any number of decisions about that person’s health and aging: Everything from whether he needs to be on hypertension medication (a question better answered by the biomarker of augmentation pressure than simple blood pressure) to therapies and lifestyle changes to slow the aging of the arteries. Biomarker testing at six-month intervals will show what’s helping and what’s not—the essence of the evidence-based approach to healthy aging.