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| |  Nerve Abnormality Causes Disabling Rapid Heart Rate, Dizziness DALLAS, TX -- Nov. 17, 1998 -- A disabling disease that causes rapid heartbeat and occurs most often in young women may be due to a pronounced abnormality in autonomic nerve activity -- the body's central control panel for vital life functions like breathing. The disease, called chronic orthostatic intolerance (COI), is often mistaken for emotional distress or other medical problems. It has been misdiagnosed as chronic fatigue syndrome, mitral valve prolapse (a malfunctioning heart valve) or panic disorder. Some patients are referred for psychiatric evaluation. Reporting in today's issue of the journal Circulation, scientists at Nashville's Vanderbilt University School of Medicine and the University of Milan, Italy, say individuals with COI lose their balance upon standing and will have a runaway heartbeat, called tachycardia. These and other symptoms including dizziness, light-headedness, tunnel vision and general discomfort can severely disrupt the lives of those with the condition, said Raffaello Furlan, M.D., of Vanderbilt and the University of Milan, the study's lead author. "People with this disorder tend to lie down most of the day," Furlan explained, adding that as many as 500,000 Americans might suffer to some degree from this problem -- and that may be a low estimate. Furlan and his colleagues said today's report is the first to describe in such detail a complex pattern of irregularities in the heart that actually form the physiological basis of the disease. "COI is not well defined in medical textbooks and thus its prevalence probably is underestimated because physicians don't know how to deal with this disorder," he said. If not correctly diagnosed and treated, COI can trigger a vicious circle of reduced physical activity due to the person's inability to stand. A person also may become more and more anxious about the condition, Furlan explained. This anxiety compounds the problem, often leading doctors to misdiagnose the condition. The research team led by Furlan and Rogelio Mosqueda-Garcia, M.D., Ph.D., studied 16 patients (11 women and five men, average age 35) with severe and long- lasting symptoms of COI. The researchers compared them with 16 healthy individuals who served as controls and tested both groups of individuals while they were lying down and after elevation on a tilt table. They found: -- COI patients have an abnormally high sympathetic output to their heart and blood vessels, even at rest that is potentially related to a central nervous system abnormality. (The sympathetic part of the autonomic nervous system serves to constrict vessels while increasing heart rate.) -- When people with COI stand, normal increases in sympathetic neural discharge to the blood vessels are blunted, compared to controls. But at the same time there is a huge increase in sympathetic activity to the heart. The result is tachycardia, a heart rate that revs as high as 120 to 130 beats per minute. But, unlike in other people who faint, there is no major drop in blood pressure in people with COI. Therefore, COI patients rarely faint. Normally, the heart rate is controlled by a balance between sympathetic and parasympathetic neural influences. When the sympathetic activity prevails, there is a shortening of the interval between beats, which means that the heart rate is higher. When parasympathetic activity is prevalent, the heart rate will slow down. The instantaneous interaction between the two neural influences generate spontaneous changes in heart rate. By analysing these changes of the heart rate with computer based techniques, it is possible to determine the state of sympathetic and parasympathetic control of the heart. When COI patients stand, Furlan said, there is a differential distribution of sympathetic nerve activity to the heart as compared to blood vessels to the rest of the body. Nerve activity to muscles, particularly in the legs, is blunted, and the body compensates by increasing heart rate to tachycardia levels. Typically patients complain that they can't stand up -- so they drastically restrict physical activity, leading to weakened muscles that only make matters worse. It is helpful to gradually increase exercise, especially swimming and other activity in water, where gravity has less impact, Furlan said. As they exercise more, the intensity of their symptoms gradually diminishes. But he says it's difficult for patients to overcome their predisposition to inactivity. Increased intake of fluids and even small amounts of salt have been shown to be beneficial, he added. Patients experience gradual improvement, but complete recovery seems to take a long time. No long-term studies have been done to accurately document actual recovery duration, Furlan explained. Therapy can also include medications, such as alpha 1-receptor agonists, drugs that mimic the body chemical that helps blood vessels constrict normally, such as midodrine.
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