Endothelial Function Testing
The endothelium is a thin membrane that lines the inside of the heart and blood vessels. Endothelial cells release substances that control vascular relaxation and contraction as well as enzymes that control blood clotting, immune function and platelet (a colorless substance in the blood) adhesion.
Endothelial dysfunction has been shown to be of significance in predicting stroke and heart attacks due to the inability of the arteries to dilate fully. The dysfunction may be a result of high blood pressure, diabetes, high cholesterol and smoking.
Studies have shown that endothelial dysfunction precedes the development of artherosclerosis, a chronic disease characterized by abnormal thickening and hardening of the arterial walls with resulting loss of elasticity. Artherosclerosis may cause a stroke or heart attack.
What Tests Are Used to Determine Endothelial Function
Acetylcholine endothelial function and adenosine coronary flow reserve tests enhance a physician's ability to diagnose and treat patients with endothelial dysfunction. The two-step test consists of:
- Administration of the drug adenosine, which normally causes the small vessels of the heart to dilate, is injected into one of the coronary arteries and the amount of blood flow is measured.
- Next, the drug acetylcholine, which normally causes dilation in the large arteries, is injected and the amount of blood flow is again measured.
If either test shows decreased blood flow to the heart muscle, a diagnosis of endothelial dysfunction and microvascular disease can be made. With evidence of insufficient blood flow to the heart muscle and open coronary arteries, medical treatment can be directed at the specific problem.
Physicians also may use non-invasive procedures to determine an artery's health and elasticity:
- Carotid Duplex Ultrasound: Ultrasound is a procedure that uses sound waves to "see" inside the body. Carotid Duplex Ultrasound is performed to evaluate symptoms including dizziness, loss of memory, stroke, loss of control of muscles and other findings that might result from narrowing or blockage of the vessels (carotid arteries) on either side of the neck.
- Pulse Wave Velocity (PWV). PWV measures, via ultrasound, the flow of blood from the carotid artery to the femoral artery (the chief artery of the thigh). By calculating the time of travel of the pulse wave, imaging specialists can determine if any blockage exists.
- Pressure Pulsation Signal. The pressure pulsation signal, using a blood pressure cuff combined with a graphic computer display, measures diastolic, systolic and mean artery pressure.
Treating Endothelial Dysfunction
Endothelial dysfunction responds favorably to a healthful diet and exercise. Exercising to maintain a healthy weight decreases a person's risk of developing certain diseases, including type 2 diabetes and high blood pressure.
Aerobic Exercise: The heart is a muscle and needs a good workout. Aerobic exercise gets the heart pumping and quickens breathing, resulting in a more efficient delivery of oxygen-carrying blood cells. Strength and flexibility training are of benefit too. Patients should always check with their physician before instituting a new exercise regimen or ratcheting up their existing routine.
Pharmacologic interventions may include:
- ACE inhibitors used for treating high blood pressure and heart failure
- Nitrate therapy
- Lipid-lowering pharmaceuticals used for managing blood cholesterol levels
- Alpha-beta blockers for blood pressure management
- Novel therapies that include ranolazine, aminophylline and experimental therapies.
External counter pulsation (ECP) therapy is another treatment option. Lying on a table or bed, pressure cuffs are fitted to the patient's thighs, hips and calves. The cuffs inflate and deflate in sync with the patient's heart rhythm, supplying the heart with extra oxygen-rich blood in the resting phase. The extra blood supply stimulates growth of the surrounding blood vessels, improving the supply of blood to the heart.