View clinical trials related to Orthostatic Intolerance.
Filter by:The main limitation patients with orthostatic intolerance (OI, or postural tachycardia syndrome, POTS) have to exercise is related to their increase in heart rate when standing. Main pharmacological treatment today is aimed at reducing heart rate with the use of betablockers (propanolol), this theoretically could also improve their exercise capacity; if their heart rate do not increase as much with the medication, they could exercise more. In addition, it has been suggested that in healthy volunteers subjected to head down tilt for 2 weeks (situation that produces a "simulated" transient POTS-like state) a single bout of intense exercise can improve orthostatic tolerance the day after exercising. The mechanisms involved in such response are not that clear but could be an increase in plasma volume already diminished in POTS patients. It seems likely that the same could be true for POTS patients. The purpose of the present study are to pharmacologically improve the amount of exercise POTS patients can perform by reducing their baseline heart rate (specific aim 1) and to evaluate next day heart responses to an acute bout of intense exercise. Therefore, the specific aims of this study are: 1. To test the hypothesis that lowering heart rate response with propanolol will result in an increase in exercise capacity. 2. To test the hypothesis that a single bout of exercise will result in an improvement in orthostatic tolerance the day after exercising.
The purpose of this study is to determine the cause of low blood pressure in selective patients who have problems with their involuntary (autonomic) nervous system. These patients frequently have had symptoms throughout their life, and their disorder might have a genetic basis. The biochemical, physiological and pharmacological procedures in this study should help us define the problem and perhaps lead to more effective treatment.
The purpose of the proposed research is to determine how changes in kidney dopamine (DA) activity influence urinary sodium excretion. We will decrease DA activity in the kidney by inhibiting DA synthesis via carbidopa administration. We want to compare findings in normal volunteers and in patients with postural tachycardia syndrome (POTS). We will test the null hypothesis (Ho) that the effects of oral carbidopa administration on urinary sodium excretion will not differ between patients with POTS and healthy volunteers.
We wish to study sleep architecture in patients with chronic orthostatic intolerance. We will test the null hypothesis that there is no difference in time during the various phases of sleep between patients and healthy control subjects.
The investigators propose to test the hypothesis that the sympathetic nervous system contributes to the cardiovascular and inflammatory abnormalities present in the chronic fatigue syndrome (CFS) and, in particular in the subset of patients characterized by postural tachycardia syndrome (POTS). CFS and POTS are seen mostly in otherwise normal young women, and are the cause of significant disability. A substantial proportion of patients referred for evaluation of POTS met diagnostic criteria for CFS and, conversely, a subset of patients referred for treatment for CFS have POTS. The investigators hypothesize that sympathetic activation underlies the pathophysiology of patients in whom CFS and POTS overlap (CFS-P).
The primary purpose of this study is to investigate the relationship between the extent of neurologic (nerve) impairment in patients with spinal cord injuries and how well the nerves passing down the spine to the heart and blood vessels are working. These nerves are called the descending spinal sympathetic pathway (DSSP) and are important in controlling many functions, including blood pressure. We also wish to examine how injury severity and DSSP function influence blood levels of nor-epinephrine and epinephrine. Nor-epinephrine and epinephrine are hormones released into the blood that are also important in controlling blood pressure. Thus, we will also look at how the effect of the extent of DSSP dysfunction influences heart rate and blood pressure and blood levels of certain enzymes.
This study will conduct tests with patients with primary chronic orthostatic intolerance (COI) to learn more about this disorder of the autonomic nervous system. Healthy normal volunteers and patients 18 years of age and older with COI may be eligible for this study. Participants undergo one or more of the following tests and procedures: - Blood studies, including arterial catheter insertion to measure blood pressure and collect arterial blood samples, blood flow studies using sensors applied to the skin and a pressure cuff around a limb, blood volume studies using injection of radioactively labeled human serum albumin and gene studies to look for genetic abnormalities associated with certain proteins. - Imaging studies, including CT scan of the adrenal glands, heart ultrasound, and PET scanning. - Electrocardiogram - Microdialysis to measures levels of chemicals in the body fluid of certain tissues. A thin tube is inserted into the skin and a solution is passed through it. Chemicals in the body tissues enter the solution in the tube. The solution is collected and the chemical levels are measured. - Neck suction. Neck suction is applied to test a reflex the brain uses to regulate blood pressure. - Perometry. Limb volume is measured using an infrared light that moves up the limb. - Quantitative sudomotor axon reflex test to evaluate an aspect of autonomic nervous system function. A small amount of a brain chemical (acetylcholine) is applied to the skin with a tiny amount of electricity, and the sweat in a nearby patch of skin is measured. - Skin electrical conduction test using sensors on the skin to measure sweat production. - Skin and core temperature measurements using sensors on the skin and in the ear canal. - Tilt table test. The subject lies on a table, secured with straps around the chest and legs. Sensors are placed on the arms and chest to monitor blood pressure, pulse rate, and heart rhythm. A catheter is placed in a vein in each arm to collect blood samples and give drugs. Another catheter is placed in an artery to draw blood and monitor blood pressure. The subject is given an infusion of norepinephrine and epinephrine, and baseline measures and blood samples are taken. The table is tilted upright and more measurements and blood samples are taken at intervals for up to 30 minutes. The table is returned to a horizontal position and additional measurements and samples may be taken. Drugs may be administered during the tests, including acetylcholine, epinephrine, and norepinephrine, radioactive chemicals used in imaging studies, and drugs that affect blood vessels, heart rate, and force of heart contractions.