Abnormal endothelium-dependent vascular relaxation in patients with essential hypertension

Article Abstract:

Blood vessels are lined with endothelial cells arranged in a sheetlike structure called the vascular endothelium. This layer is known to modulate the activity of the smooth muscle cell layer that surrounds it, whose primary function is contraction, leading to a constricted vessel. Thus, the endothelium is able to affect vascular tone. These effects are exerted on resistance vessels (the smallest arteries and arterioles) that determine peripheral resistance to blood flow and, ultimately, blood pressure. It is possible that vascular endothelium loses its normal ability to affect vessel diameter in some disease states, such as hypertension (high blood pressure). This was tested by evaluating 18 hypertensive patients and 18 nonhypertensive controls with respect to the responses of their blood vessels when vasoactive substances (agents that affect the blood vessels) were infused. The substances were acetylcholine (a vasodilator that acts by inhibiting the release of norepinephrine, a substance that causes constriction, at nerve endings on the blood vessel) and sodium nitroprusside (a direct dilator of smooth muscle in the vessel). Blood vessel responses were measured by plethysmography (a method of measuring size changes) that recorded size changes in the nondominant forearm. Any increase in blood flow would register as increased size. Results showed that blood flow and percent of change in vascular resistance were significantly higher in normal subjects after acetylcholine than in hypertensive patients. At the highest dose, blood flow in the forearm was approximately 20 milliliters per minute for controls, and only nine milliliters per minute for patients. There were no differences between the groups in blood flow after sodium nitroprusside. Other research has shown that acetylcholine cannot induce vasodilation if blood vessel endothelium is damaged, apparently because the endothelium releases a substance that relaxes the smooth muscle (endothelium-derived releasing factor). A discussion of the effects of acetylcholine is provided. An endothelial abnormality in hypertensive people could elevate the blood pressure even more, although whether this effect is the cause, or result, of the hypertension is not known. In any event, endothelium that does not function normally could contribute to hypertension, regardless of the disorder's origin. (Consumer Summary produced by Reliance Medical Information, Inc.)

Hypertension, Measurement, Development and progression, Peripheral vascular diseases, Acetylcholine, Blood vessels, Vascular endothelium, Vascular smooth muscle

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Enhanced detection of ischemic but viable myocardium by the reinjection of thallium after stress-redistribution imaging

Article Abstract:

In coronary artery disease (CAD), one or more of the major arteries that bring blood to the heart is narrowed to less than half its normal diameter by plaques of fat, cholesterol and accumulated cells. This narrowing reduces the blood supply to the heart muscle, and if an artery becomes completely blocked, a myocardial infarction (MI, heart attack) results. An MI may cause permanent damage to the portion of the heart muscle that is served by the blocked artery; the tissue may actually die. However, in CAD patients, small areas of the heart may actually be "hibernating", rather than dead, if the blood supply to them is reduced; inadequate blood flow is known as ischemia. These ischemic, but viable regions may appear to be dead tissue during tests done to evaluate heart blood flow. It is important to determine whether these regions represent dead or viable tissue, but this has been difficult to do. This issue was addressed by studying 100 patients with stable CAD. The patients underwent exercise (stress) testing, during which thallium, a radioactive substance, was injected and images were obtained to evaluate the pattern of blood flow to the heart. A new technique was used; in addition to the standard thallium injection during exercise, followed by the redistribution images (referring to redistribution of blood flow after exercise) taken several hours later, another dose of thallium was given after the redistribution images. The images taken after the second thallium injection improved the ability of physicians to recognize ischemic but viable regions of heart muscle; of 85 regions that appeared to be dead tissue after redistribution imaging, 42 showed improved blood flow after the second thallium injection. This information can be used to identify patients who will probably experience an improvement in the function of the left ventricle after undergoing procedures to improve coronary blood flow, such as angioplasty or coronary artery bypass surgery. (Consumer Summary produced by Reliance Medical Information, Inc.)

Methods, Testing, Heart, Treadmill exercise tests, Thallium

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Sudden cardiac death without warning: possible mechanisms and implications for screening asymptomatic populations

Article Abstract:

Sudden death is a common presenting manifestation of coronary artery disease. It will be useful to determine whether screening tests can identify persons at risk of sudden death. Three studies in which asymptomatic subjects were followed prospectively after having undergone electrocardiographic exercise stress testing demonstrated a disturbing fact: the large low-risk group with normal responses to exercise testing contained the large majority of subjects who later died suddenly.

Complications and side effects, Arteries, Cardiac arrest, Arterial stenosis, column

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