Orthostatic Intolerance

VOL. IV NO. IV JULY/AUGUST 2002 306 When a syndrome has many different names, you can be sure of two things: first, it is common, and second, it is poorly understood. Such is the case with orthostatic intolerance, which, according to Dr. David Robertson,1 who has made a career of studying it and related conditions, has been given at least 18 different titles, including neurocirculatory asthenia, mitral valve prolapse syndrome, postural orthostatic tachycardia syndrome, and hyperadrenergic orthostatic tachycardia. It is now officially recognized as orthostatic intolerance (OI) by the American Autonomic Society. It may overlap with chronic fatigue syndrome. It is characterized by an exaggerated increase in heart rate (of more than 30 beats/minute) on standing with only a small decrease of blood pressure. This distinguishes it from orthostatic hypotension, which is defined by a fall of blood pressure of 20/10 mm Hg or more. Robertson has described it as an epidemic,1 not because its prevalence is increasing, but because it is common (in perhaps 500,000 Americans), although it is still not recognized by many practitioners. For reasons that are quite obscure, the syndrome is five times as common in women as in men, and typically presents between the ages of 15 and 45. It is actually not uncommon in children, and much of the research has been done by pediatricians. As with other syndromes where the etiology is obscure, the symptoms are many and vague. They include lightheadedness, dizziness, anxiety, fatigue, and palpitations. A key feature is that all are made worse by the upright posture, and are relieved by lying down. This is an important point to remember when we are taking histories from our patients, because unless we specifically ask if such symptoms are related to posture, we may miss the diagnosis. Da Costa2 first described the phenomenon of orthostatic tachycardia in soldiers of the Union Army during the US Civil War who were complaining of fatigue, dizziness, headache, and chest pain, noting that “the immediate effect of the exchange of position was most striking.” While it is easy to attribute these symptoms to stress and anxiety, several of the soldiers first developed their symptoms after a long march or an attack of diarrhea, suggesting that dehydration might have been a contributory factor. This condition was subsequently referred to as the Irritable Heart syndrome. During World War I, Sir Thomas Lewis3 described the same set of symptoms as Soldier’s Heart or the Effort Syndrome. He too noted the marked orthostatic tachycardia. The principal signs and symptoms of OI are consistent with a failure to adjust the circulation to the upright posture, as if there were an inadequate blood volume. When we stand up, there is a sudden pooling of about 700 mL of blood in the abdomen and legs.4 Our baroreceptor reflexes normally compensate for this very rapidly, and there is an increased heart rate, cardiac output, and vasoconstriction. If the autonomic nervous system is deficient, as in patients with idiopathic orthostatic hypotension, there is a gradual decrease of blood pressure until the brain is no longer adequately perfused and there is a gradual loss of consciousness. Patients with OI show an intermediate form of this phenomenon. The symptoms and physiologic manifestations of OI closely resemble those of the deconditioning which occurs after prolonged bedrest or spaceflight.5 Some people with OI become so disabled by the condition that they drastically reduce Orthostatic Intolerance