Pathophysiology, diagnosis, and treatment of orthostatic hypotension and vasovagal syncope.

Orthostatic hypotension (OH) occurs in 0.5% of individuals and as many as 7-17% of patients in acute care settings. Moreover, OH may be more prevalent in the elderly due to the increased use of vasoactive medications and the concomitant decrease in physiologic function, such as baroreceptor sensitivity. OH may result in the genesis of a presyncopal state or result in syncope. OH is defined as a reduction of systolic blood pressure (SBP) of at least 20 mm Hg or diastolic blood pressure (DBP) of at least 10 mm Hg within 3 minutes of standing. A review of symptoms, and measurement of supine and standing BP with appropriate clinical tests should narrow the differential diagnosis and the cause of OH. The fall in BP seen in OH results from the inability of the autonomic nervous system (ANS) to achieve adequate venous return and appropriate vasoconstriction sufficient to maintain BP. An evaluation of patients with OH should consider hypovolemia, removal of offending medications, primary autonomic disorders, secondary autonomic disorders, and vasovagal syncope, the most common cause of syncope. Although further research is necessary to rectify the disease process responsible for OH, patients suffering from this disorder can effectively be treated with a combination of nonpharmacologic treatment, pharmacologic treatment, and patient education. Agents such as fludrocortisone, midodrine, and selective serotonin reuptake inhibitors have shown promising results. Treatment for recurrent vasovagal syncope includes increased salt and water intake and various drug treatments, most of which are still under investigation.

Present-day uses of niacin: effects on lipid and non-lipid parameters.

Existing guidelines for the prevention and treatment of coronary artery disease focus on lowering low-density lipoprotein cholesterol (LDL-C) as the primary lipid target. However, there has been increasing interest in raising high-density lipoprotein cholesterol (HDL-C) due to strong evidence linking low HDL-C levels with an increased risk of atherosclerosis. Raising HDL-C levels with lifestyle changes and pharmacologic interventions appear to reduce the risk of coronary artery disease beyond that of lowering LDL-C alone. Niacin has a substantial HDL-C raising effect, and also may beneficially alter total cholesterol, LDL-C and triglyceride levels. Niacin also exhibits antioxidant, anti-inflammatory and other beneficial effects on atherosclerosis. Niacin is safe and effective to use in women, in patients with diabetes mellitus and/or metabolic syndrome, and when used in combination with statins. Niacin has the promise of being a powerful pharmacologic agent in the fight against atherosclerotic disease, although additional clinical studies are required to examine this further.

Relation of postural vasovagal syncope to splanchnic hypervolemia in adolescents.

BACKGROUND: The mechanisms of simple faint remain elusive. We propose that postural fainting is related to excessive thoracic hypovolemia and splanchnic hypervolemia during orthostasis compared with healthy subjects. METHODS AND RESULTS: We studied 34 patients 12 to 22 years old referred for multiple episodes of postural faint and 11 healthy subjects. Subjects were studied in the supine position and during upright tilt to 70 degrees for 30 minutes and subgrouped into S+, historical fainters who fainted during testing (n=24); S-, historical fainters who did not faint during testing (n=10); and control subjects. Supine venous occlusion plethysmography showed no differences between blood flows of the forearm and calf in S+, S-, or control. Cardiac index, total peripheral resistance, and blood volume were not different. Using impedance plethysmography, we assessed blood redistribution during upright tilt. This demonstrated decreased thoracic blood volume and increased splanchnic, pelvic, and leg blood volumes for all subjects. However, thoracic blood volume was decreased in S+ compared with control volume, correlating well with the maximum upright heart rate. Splanchnic volume was decreased in the S+ and S- groups, correlating with the change in thoracic blood volume. Pelvic and leg volume changes were similar for all groups and uncorrelated to thoracic blood volume. CONCLUSIONS: Enhanced postural thoracic hypovolemia and splanchnic hypervolemia are associated with postural simple faint.