patient site

 


patient site

 


patient site

 

9  

CardioAge - Arterial Stiffness Testing

 

As early as the 1600's, Thomas Sydenham, known as the English Hippocrates, said "a man is as old as his arteries."

It's all in the pulse. Today we know that what Mr. Sydenham said holds true for women as well. Even before him, Chinese doctors knew that you could tell a lot about the age of a person's cardiovascular system just by feeling the pulse at the wrist. The SphygmoCor device updates this hallowed practice by replacing the doctor's fingers with a highly sensitive pressure probe to record the shape of the radial artery pulse wave. 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. Similar to the way an ECG tracing gives us information about the health of the heart by displaying a summary of its electrical activity as it travels throughout the contracting heart muscle, the arterial pulse wave shape offers information about the health of the arterial system as blood moves through it during the pulsatile cardiac cycle.

 

Central blood pressure is what matters. The SphygmoCor software analyses the shape of the pressure wave at the wrist and then determines the pressure in the aorta as it comes off the heart. The pressure in the aorta is different from that in the arm (where blood pressure is traditionally measured) because of the effect of what is called the "reflected wave". As the heart pumps out a large amount of blood, the elastic aorta expands to accept the increased volume causing the pressure to increase less than if it were a rigid tube. The pressure wave then travels down the aorta to the legs and arms where it meets the smaller arteries feeding the capillary beds of your organs. The drop in pressure at these resistance arteries causes a reflected wave to return to the
aorta.

 

Arteries stiffen and constrict with age. The aorta and other large arteries stiffen from a loss of elastin and crosslinking of collagen. This stiffening causes the reflected wave to travel back to the heart faster so that it rushes into the
last bit of blood coming out of the heart in the aorta at the end of systole. The increased central pressure as a result of the collision of the forward and reflected waves occurs in the aorta but not in the arms, and is called the augmentation pressure (AP). The amount of augmentation pressure is dependent not only on the speed of the reflected wave, but also on how much resistance the forward wave meets when it hits the smaller vessels. Thus, the AP combines the two major facets of arterial aging - stiffening of the large arteries and constriction of the resistance arteries - into a single parameter that increases linearly with age. The CardioAge is created by comparing your AP with that of 4001 healthy
(no other cardiac risk factors), men and women aged 18 to 90 years old.

Why is the CardioAge Important?


» It increases linearly with age and tells you how well your arteries are aging starting at a very young age - the time to start acting
» It reflects the pressure your brain, kidneys, and heart experience and therefore better predicts disease of these organs than arm blood pressure
» It can tell you better than arm blood pressure if your patient needs to be on anti-hypertensive medication or, if they are on therapy, how well it's working.

What factors affect the CardioAge?


Age: It takes time for all of the following risk factors to affect the arteries.
Sedentary vs. active lifestyle: Activity, in particular vigorous exercise, increases the production of nitric oxide in the small arteries, which decreases AP. Chronic aerobic exercise lowers the resting heart rate, which decreases the
total number of times the heart beats in a day.

Height: Taller people have lower central pressures because the reflected wave takes longer to travel back up the aorta to the heart.
Gender: Women have slightly stiffer arteries than men, even after adjusting for height. The CardioAge is genderadjusted.
Smoking: After having a cigarette, even in young people, AP is increased because it causes constriction of the resistance arteries. Despite this increase in central pressure, arm blood pressure often remains deceptively low in young smokers. With years of smoking, the large arteries stiffen more rapidly
and the smaller arteries become clogged - both of these processes increase the CardioAge.
Obesity: Increased abdominal fat has been associated with increased arterial stiffness independent of arm blood pressure, age, and ethnic group.
Cholesterol: High total and LDL cholesterol levels have been associated with increased arterial stiffness. Thus, cholesterol-lowering medications can lower the CardioAge.
Caffeine: Consumption of caffeinated coffee has been associated with increased AP, even after one cup, without a similar increase in arm blood pressure. If your patient had a cup of a caffeinated drink within 2 hours of their test, their CardioAge could be somewhat higher.
Hormones: Low testosterone increases AP in men undergoing androgen deprivation therapy. Growth hormone deficiency is associated with increased arterial stiffness.

Blood pressure medications: The more recent blood pressure medications, such ACE inhibitiors, angiotensin receptor blockers, and calcium channel blockers, lower the augmentation pressure and therefore the CardioAge. Beta
blockers, such as atenolol, propranolol, and metoprolol can actually increase the CardioAge. Diuretics often have a neutral effect.

 

The CardioAge is determined with a proprietary algorithm using certain aspects of the output from the SphygmoCor device.

What do the measurements mean?

 

Augmentation Index (AIx)
Augmentation Index is a measure of the stiffness of your arteries. High cholesterol, smoking, diabetes, and aging can all cause the vessels that take blood from the heart (the arteries) to become stiffer. As the arteries become stiffer the heart must work harder due to the extra load on the heart.

 

Ejection Duration (ED)
Each time our heart beats, it has a time when it is contracting and pumping blood out of the heart, and a time when it is resting and filling with blood. The ED is a measurement of how much time the heart spends pumping. When the heart spends a shorter time than normal pumping there may be problems with the ability to pump blood, while longer than normal pumping time may indicate problems with the ability for the heart to relax and fill with blood.

 

Subendocardial Viability Ratio (SEVR)
When the heart is resting, the heart muscle is supplied with oxygen for energy. When the heart is contracting and pumping this energy is being used. The SEVR is a measure of the ability of the arterial system to meet the heart’s energy requirements. As this ratio decreases, the heart has less energy reserves available and may have a lower tolerance for physical activity.

How is a Pulse Wave Analysis Assessment done?

 

The test is simple and painless, taking only a few minutes to perform. While the patient is laying in a comfortable position, the technician will place a pencil-like sensor gently against the wrist and record a blood pressure signal from the pulse. From this recording, the Pulse Wave Analysis system will calculate the pressure waveform at the heart and provide you with cardiovascular measurements such as Alx, ED and SEVR.

 

For more information on wave reflection, visit Atcor Medical's excellent tutorial presentation and flash animation. 

 

Sample report (PDF)

 

CardioAgesm

 

NEXT: CutoAge