ISSN:0002-9629    

出版商:OVID    

年代:1999

数据来源: OVID

摘要:

Several of the pathophysiological mechanisms resulting in orthostatic intolerance (ie, tachycardia) have been recognized individually over the course of the past 100 years or more. More recent definitions of the normal ranges of orthostatic blood pressure and heart rate changes have facilitated the recognition of pathogenetic disorders that are probably shared in various proportions between orthostatic intolerance and various types of orthostatic hypotension. These include autonomic dysfunction of (1) the leg veins almost invariably causing excessive gravitational blood pooling, usually associated with (2) hypovolemia of circulating erythrocytes and plasma that is probably attributable to impaired autonomic stimulation of erythropoietin production, renin release, and (less consistently) aldosterone secretion. Improved understanding of these apparent results of lower body dysautonomia should facilitate more effective therapy in the future.

ISSN:0002-9629    

出版商:OVID    

年代:1999

数据来源: OVID

摘要:

Upright posture imposes a substantial gravitational stress on the body, for which we are able to compensate, in large part because of the autonomic nervous system. Alteration in autonomic function, therefore, may lead to orthostatic intolerance. On one extreme, patients with autonomic failure caused by degenerative loss of autonomic function are severely disabled by orthostatic hypotension and may faint whenever they stand up. Fortunately, such patients are relatively rare. On the other hand, disabling orthostatic intolerance can develop in otherwise normal young people. These patients can be severely impaired by symptoms of fatigue, tachycardia, and shortness of breath when they stand up. The actual incidence of this disorder is unknown, but these patients make up the largest group of patients referred to centers that specialize in autonomic disorders. We will review recent advances made in the understanding of this condition, potential pathophysiological mechanisms that contribute to orthostatic intolerance, therapeutic alternatives currently available for the management of these patients, and areas in which more research is needed.

ISSN:0002-9629    

出版商:OVID    

年代:1999

数据来源: OVID

摘要:

Neurally mediated syncope may occur in patients whose hemodynamic picture does not fit the characteristics of orthostatic intolerance as described elsewhere in this issue. Nonetheless, patients who suffer from neurocardiogenic or vasovagal syncope may be seriously incapacitated by their episodes of syncope or presyncope. Although it has been assumed that vagal activation as a result of stimulation of ventricular mechanoreceptors is essential to the production of these episodes, several critical observations are presented that suggest that other mechanisms may also be operative in some patient subsets. In addition, evidence is presented that the sympathetic responses of many of these patients may be reduced rather than increased and that abnormal baroreflex responsiveness may also play an causative role. These findings suggest new avenues for therapy in this field in which carefully controlled, randomized, double-blind trials are scarce.

ISSN:0002-9629    

出版商:OVID    

年代:1999

数据来源: OVID

摘要:

Upright tilt testing is commonly used in the evaluation of patients with syncope to provoke hypotension and/or bradycardia in the laboratory. The most common type of response is provocation of neurally mediated syndrome (vasovagal syncope). The American College of Cardiology Expert Consensus has proposed indications for tilt testing. The most common indication is recurrent syncope of unexplained cause. Upright tilt testing methods have not been standardized. The most common protocols in this country use a tilt angle of 60-80° and use isoproterenol infusion after a period of drug-free tilt testing. The sensitivity of upright tilt testing is estimated to be 67-83%, and the specificity is between 75 and 100%. The reproducibility of the test has been variable. In patients with unexplained syncope, positive responses are found to be 50% without the use of isoproterenol and 64% with the use of isoproterenol. Many different treatments have been used. At this time, there is no consensus regarding the most effective treatment. β-blockers and fludrocortisone plus salt are the most commonly used drugs. Pacemakers have been used, but their role is ill-defined at this time.

ISSN:0002-9629    

出版商:OVID    

年代:1999

数据来源: OVID

摘要:

Chronic fatigue syndrome (CFS) or myalgic encephalomyelitis is a clinically defined syndrome characterized by persistent or relapsing debilitating fatigue for longer than 6 months in the absence of any definable medical diagnosis. The cause of this syndrome is unknown. Symptoms of orthostatic intolerance, such as disabling fatigue, dizziness, diminished concentration, tremulousness, and nausea, are often found in patients with CFS. In this review, we critically evaluate the relationship between orthostatic intolerance and CFS. Particular emphasis is placed on clinical diagnosis, laboratory testing, pathophysiology, and therapeutic management. It is hoped that this review will provide a stimulus for further study of this complex and disabling condition.

ISSN:0002-9629    

出版商:OVID    

年代:1999

数据来源: OVID

摘要:

Patients with the postural orthostatic tachycardia syndrome (POTS) have symptoms of orthostatic intolerance despite having a normal orthostatic blood pressure (BP), which suggests some impairment of cerebrovascular regulation. Cerebrovascular autoregulation refers to the maintenance of normal cerebral blood flow in spite of changing BP. Mechanisms of autoregulation include myogenic, metabolic and neurogenic vasoregulation. Beat-to-beat recording of blood-flow velocity (BFV) is possible using transcranial Doppler imaging. It is possible to evaluate autoregulation by regressing ΔBFV to ΔBP during head-up tilt. A number of dynamic methods, relating ΔBFV to ΔBP during sudden induced changes in BP by occluding then releasing peripheral arterial flow or by the Valsalva maneuver. The ΔBFV to ΔBP provides an index of autoregulation. In orthostatic hypotension, the autoregulated range is typically expanded. In contrast, paradoxical vasoconstriction occurs in POTS because of an increased depth or respiration, resulting in hypocapnic cerebrovascular constriction, and impaired autoregulation.

ISSN:0002-9629    

出版商:OVID    

年代:1999

数据来源: OVID

摘要:

Adult respiratory distress syndrome (ARDS) complicating the course of fulminant hepatic failure is nearly always fatal without orthotopic liver transplantation. We report the case of a 50-year-old woman with fulminant hepatic failure and ARDS that resolved after her recovery from the acute liver failure without liver transplantation. The pathogenesis is discussed, particularly with regard to liver-lung interactions.

ISSN:0002-9629    

出版商:OVID    

年代:1999

数据来源: OVID

摘要:

Pneumocystis cariniipneumonia (PCP) presenting as bilateral upper-lobe cavitary disease is rare. Isolated upper-lobe involvement has traditionally been associated with aerosolized pentamidine prophylaxis. Dapsone is a cheap and effective prophylactic agent againstP cariniiin patients who cannot tolerate trimethoprim-sulfamethoxazole. This is a case of a man who presented with bilateral upper-lobe cavitaryP cariniipneumonia despite being on dapsone prophylaxis. Bronchoalveolar lavage was negative forP carinii. Transbronchial biopsy was positive forP carinii. The patient improved significantly with radiological resolution on specific treatment forP carinii. PCP should be included in the differential diagnosis of upper-lobe cavitary lung disease, and a transbronchial biopsy should be performed when the diagnosis is suspected.

ISSN:0002-9629    

出版商:OVID    

年代:1999

数据来源: OVID