Orthostatic hypotension in human immunodeficiency virus infection may be the result of generalized autonomic nervous system dysfunction

Article Abstract:

Orthostatic hypotension (OH) has been found to occur in patients who are infected with the human immunodeficiency virus (HIV). OH is the development of low blood pressure when a person stands up, and can be caused by various types of medications, dehydration or infection. Five patients who were infected with HIV, who had OH which was not due to the usual causes, were evaluated by testing of the autonomic nervous system. The autonomic nervous system controls the functions necessary for life that are involuntary, such as contraction of the heart muscle and smooth muscles, the heart rate, blood pressure and the activity of the glands. Abnormalities in the autonomic nervous system were detected in all five patients. These abnormalities were seen in both the sympathetic nervous system (which increases the heart rate, constricts blood vessels and increases the blood pressure) and the parasympathetic nervous system (which decreases the heart rate, increases the activity of glands and increases the movement of substances through the intestines). This indicates that the OH was associated with general dysfunction of the autonomic nervous system of the individuals infected with HIV. The OH was present for only relatively short periods of time and was not chronic, as it often is with other diseases. The OH was treated with the corticosteroid fludrocortisone, which was effective in four out of the five patients. (Consumer Summary produced by Reliance Medical Information, Inc.)

Evaluation, Causes of, HIV infection, HIV infections, Nervous system, Parasympathetic, Parasympathetic nervous system, Hypotension, Orthostatic, Orthostatic hypotension, Fludrocortisone

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Hypophosphatemia complicating management of acute severe asthma

Article Abstract:

Patients admitted to a hospital intensive care unit for severe asthma were evaluated for hypophosphatemia (low blood phosphorus level). It has been suggested that hypophosphatemia can have dangerous effects in such patients by reducing the contractility of the diaphragm muscle, which is important for breathing, and decreasing the oxygenation of body tissues. Eighteen patients admitted with severe asthma all showed a substantial decrease in blood phosphorus levels after asthma treatment; the hypophosphatemia was severe in four of the patients. The mechanism behind the drop in phosphorus levels appeared to be linked to a change in the acid-base balance of the blood; patients were recovering from respiratory acidosis, meaning their blood pH was rising towards normal. Phosphorus in the blood may move into cells while respiratory acidosis is resolving;this would cause phosphorus levels in the blood to subjects. Replacement phosphorus was not given during the several days it took for levels to return to normal. These individuals did not experience any adverse reactions due to the hypophosphatemia, probably because it resolved quickly. But the condition can cause fatigue of the diaphragm, thereby affecting breathing, so phosphorus levels should be monitored while acute severe asthma is being treated. (Consumer Summary produced by Reliance Medical Information, Inc.)

Care and treatment, Research, Asthma, Metabolism, Acidosis, Phosphorus (Chemical element), Acid-base imbalances, Acid-base imbalance, Phosphorus metabolism

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Profound sympathoinhibition complicating hypovolemia in humans

Article Abstract:

Hypovolemic shock is a physical collapse due to low levels of circulating blood. The reflex adjustments to hypovolemic shock include tachycardia, where the heart muscle contracts at a rate greater than 100 beats per minute, and constriction of the blood vessels. However, it has been shown that bradycardia, involving the slowing of the heartbeat and inhibition of the sympathetic nervous system, can occur when there are low levels of circulating blood in the heart. A case study is reported of a normal subject in whom marked hypovolemia was simulated. Bradycardia and a sympathoinhibitory response, which resulted in a decrease in heart rate, occurred when there was a marked decrease in the blood pressure of the heart. The possibility that this paradoxical response of the slowing of the heart rate and inhibition of the sympathetic nerves in response to hypovolemic shock could occur should be recognized by physicians that might be confused by these findings during treatment of patients in shock. (Consumer Summary produced by Reliance Medical Information, Inc.)

Tachycardia, Bradycardia, Shock

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