The July issue of The American Journal of Medical Sciences presents a special symposium on the measurement and clinical implications of blood volume and its measurement.
The Journal is published by the Southern Society for Clinical Investigation and Lippincott Williams & Wilkins, part of Wolters Kluwer Health, provider of leading healthcare content, context and consulting. With more convenient measurement techniques, testing of blood volume may play a more visible role in the management of medical conditions such as heart failure, syncope (fainting), and others.
The ten papers in the symposium provide timely updates on traditional and newer techniques for measuring blood volume, its role in specific diseases, and key influencing factors—including the role of physical activity in maintaining blood volume with aging, which may help to explain the benefits of physical fitness in preventing cardiovascular disease.
New techniques have removed obstacles to the clinical measurement of blood volume, according to an introductory editorial by Drs. Satish R. Raj and David Robertson of Vanderbilt University School of Medicine. "This is fueling a resurgence of interest and discovery in this field," they write. "The blood volume phoenix has clearly arisen." The symposium was supported by an unrestricted educational grant from the American Foundation for Safe Blood in Healthcare.
Traditionally, blood volume has been measured by indirect techniques. The most familiar test is the hematocrit level—the ratio of red blood cells to whole blood volume, often used as a sign of anemia (low levels of red blood cells or hemoglobin, which carries oxygen in the blood). However, the hematocrit level does not reflect the actual red blood cell volume and can be affected by a wide range of factors, including the patient's body position. A recently approved test using a single radiotracer provides faster and more convenient results than previous "double-labeled" radioisotope techniques. This may facilitate the use of blood volume measurements for routine clinical purposes.
Blood volume is a key consideration in patients with several specific diseases and conditions. In congestive heart failure, blood volume measurements are a close indicator of more invasive tests of heart function. Unrecognized volume overload can worsen the symptoms of congestive heart failure. Ongoing studies will help to clarify the role of blood volume measurement in heart failure.
Measurement of blood volume can also provide clues to the causes of unexplained syncope, or fainting. Testing is especially important, as patients with syncope may have various blood volume abnormalities, some of which are not helped by the standard "empiric" treatments. Low blood volume has also been linked to postural tachycardia syndrome—a condition of posture-related heart rhythm abnormalities.
Several articles discuss the interrelated body systems that influence blood volume. Studies of a condition called failure of the autonomic nervous system lend insights into how the sympathetic nervous system contributes to maintaining normal blood volume. The symposium also includes a detailed overview of how the kidneys work to regulate blood volume by controlling plasma volume and red cell mass.
Another paper lends important insights into how physical activity and inactivity affect blood volume, particularly in older adults. Blood volume was previously thought to decrease with aging, but recent studies suggest that the true cause may be a sedentary "Western" lifestyle and a high-calorie diet. Author Victor A. Covertino, Ph.D., concludes: "Perhaps one of many important benefits of maintaining physical activity and fitness during aging is the resultant expansion of plasma and blood volume that provides a protective effect against development of cardiovascular disease."
About The American Journal of the Medical Sciences
Founded in 1820, The American Journal of the Medical Sciences is the official journal of the Southern Society for Clinical Investigation. Regular features include the Southwestern Internal Medicine Conference, Cardiology Grand Rounds of the University of North Carolina, the Consortium for Southeastern Hypertension Control, and Case Records of the VA Maryland Healthcare System/University of Maryland Medicine, as well as original articles dealing with topics such as infectious disease, rheumatology/immunology, hematology/oncology, allergy, and endocrinology. Visit the journal website at http://www.amjmedsci.com.
About Lippincott Williams & Wilkins
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