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Results 451 - 500 of 1579
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Mathias C J - - 2004
Water drinking recently has been shown to raise blood pressure in normal subjects and in patients with autonomic failure who have orthostatic hypotension. However, in normal young subjects, ingestion of approximately 500 ml has no pressor effect; but in older subjects there is an increase in blood pressure. An even ...
Bjarnegård N - - 2004
AIMS: The mechanical properties of arteries play a major role in the regulation of blood pressure and cardiac performance. The effect of sympathetic stimulation on the mechanical properties of the proximal brachial artery was analysed in 18 healthy volunteers, nine young (25 +/- 2 years) and nine elderly (69 +/- ...
Weisbrod Cara J - - 2004
We compared haemodynamic and peripheral vasomotor responses to lower body negative pressure (LBNP) in cardiac transplant recipients who had undergone bicaval anastomoses, involving right atrial deafferentation (-RA), and the conventional procedure in which some atrial baroreceptor afferents remain intact (+RA). We measured mean forearm blood flow (FBF) responses using Doppler/ultrasound ...
Gisolf Janneke - - 2004
OBJECTIVES: We set out to determine the effect of sublingual nitroglycerin (NTG), as used during routine tilt testing in patients with unexplained syncope, on hemodynamic characteristics and baroreflex control of heart rate (HR) and systemic vascular resistance (SVR). BACKGROUND: Nitroglycerin is used in tilt testing to elicit a vasovagal response. ...
Edwards Michael R - - 2004
Electrodermal activity (EDA) increases during arousal, emotional stimuli or thermoregulatory sweating and is sometimes apparent in unfiltered ECG recordings. We hypothesized that changes in EDA precede any change in blood pressure (BP) or cerebral blood velocity (CBV) observed at syncope. Data from 70 patients referred for recurrent syncope were retrospectively ...
Pitt Marjorie S - - 2004
Crouching then standing induces large changes in arterial blood pressure. Ingestion of carbohydrate and water are known to have contrasting effects on cardiovascular control in patients with various forms of autonomic dysfunction. We tested the hypothesis that, in patients with attacks of posturally related (neurogenic or vasovagal) syncope, postural maneuvers ...
Sahul Zakir H - - 2004
BACKGROUND: Tachypacing has been suggested to compensate for drop in blood pressure as a technique to improve symptoms in patients with severe orthostatic hypotension secondary to autonomic dysfunction. To date, however, no randomized controlled studies have been performed to validate the approach. METHODS AND RESULTS: Six patients with severe orthostatic ...
Maurer Mathew S - - 2004
BACKGROUND: Orthostatic hypotension (OH) is traditionally defined as a decline in systolic or diastolic blood pressure of >20 or >10 mm Hg, respectively, after 1 or 3 minutes of upright posture. OH is common in the elderly, but has not been consistently demonstrated to be an independent risk factor for ...
Young Trudie - - 2004
Manual repositioning of patients by nursing staff is a recognised technique for preventing pressure ulcer formation. The 30 degree tilt is a method of positioning patients that, in the laboratory setting, reduced the contact pressure between the patient and the support surface. A randomised controlled trial was used to examine ...
Singh K - - 2004
Systolic time intervals (STI) are sensitive indices of myocardial function. The present study was conducted to evaluate the effect of orthostatic stress on STI before and after 70 degrees head up tilt (HUT) in rabbits. Electrocardiogram (ECG), phonocardiogram and carotid arterial pulse were recorded simultaneously on four channel polyrite (INCO). ...
Balocchi R - - 2004
Orthostatic intolerance is the most serious symptom of cardiovascular deconditioning induced by microgravity. We have showed that in symptomatic subjects the baroreflex control of sinus node is affected by short term simulated microgravity. At present the influence of the respiration on the cardiovascular system in this condition is not clear. ...
Claydon V E - - 2004
Orthostatic tolerance is a measure of the ability to prevent hypotension during gravitational stress. It is known to be dependent on the degree of vasoconstriction and the magnitude of plasma volume, but the possible influence of packed cell volume (PCV) is unknown. High altitude residents have high haematocrits and probably ...
Platts Steven H - - 2004
Many astronauts exhibit post-spaceflight orthostatic hypotension due to inadequate norepinephrine release when in an upright posture. We hypothesized that an alpha1-adrenergic agonist, midodrine, would be an effective countermeasure. A female astronaut, who had problems with postflight orthostatic hypotension after a previous flight, consumed 10 mg midodrine after a subsequent flight, ...
Smit Adrianus A J - - 2004
The aim of this study was to investigate in patients with neurogenic orthostatic hypotension the mechanism and usefulness of abdominal compression to increase standing blood pressure. In three protocols, 23 patients underwent abdominal compression. Protocol 1 evaluated in a 40-60 degrees head-up-tilt position, the effect of abdominal compression on caval ...
Yamazaki Fumio - - 2004
To test the hypothesis that tolerance to central hypovolemic stress is diminished with a reduced sensitivity of cardiac baroreflex in young and old men, twenty-four healthy elderly male subjects (67.5+/-0.9 yrs) and 24 young male subjects (22.4+/-0.4 yrs) underwent a 21 min bout of ramped lower body negative pressure (LBNP) ...
Yanagiya Yusuke - - 2004
A bionic baroreflex system (BBS) is a computer-assisted intelligent feedback system to control arterial pressure (AP) for the treatment of baroreflex failure. To apply this system clinically, an appropriate efferent neural (sympathetic vasomotor) interface has to be explored. We examined whether the spinal cord is a candidate site for such ...
Convertino Victor A - - 2004
We measured various hemodynamic responses and muscle sympathetic nerve activity (MSNA) in human subjects during a graded lower-body negative pressure (LBNP) protocol to test the hypotheses that: (1) reduced stroke volume (SV) is linearly related to increased MSNA; and (2) the onset of symptoms of impending cardiovascular collapse is associated ...
Sun Biao - - 2004
This study was designed to clarify whether simulated microgravity-induced differential adaptational changes in cerebral and hindlimb arteries could be prevented by daily short-period restoration of the normal distribution of transmural pressure across arterial vasculature by either dorsoventral or footward gravitational loading. Tail suspension (Sus) for 28 days was used to ...
O'Leary Deborah D - - 2004
Beat-by-beat estimates of total peripheral resistance (TPR) can be obtained from continuous measurements of cardiac output by using Doppler ultrasound and noninvasive mean arterial blood pressure (MAP). We employed transfer function analysis to study the heart rate (HR) and vascular response to spontaneous changes in blood pressure from the relationships ...
Harinath Kasiganesan - - 2004
OBJECTIVES: To evaluate effects of Hatha yoga and Omkar meditation on cardiorespiratory performance, psychologic profile, and melatonin secretion. SUBJECTS AND METHODS: Thirty healthy men in the age group of 25-35 years volunteered for the study. They were randomly divided in two groups of 15 each. Group 1 subjects served as ...
Lee Kichang - - 2004
The reproducibility of heart rate variability (HRV) measures during graded lower body negative pressure (LBNP) have not been studied in sufficient detail. Active college age men (n=14) underwent an orientation exposure and two trials of graded LBNP to presyncope or -100 mmHg, separated by 1 week. Heart rate, stroke volume ...
Ichinose Masashi - - 2004
We tested the hypothesis that in humans, carotid-baroreflex dynamic responses (evaluated by examining the time course of the carotid-baroreflex-induced alterations in muscle sympathetic nerve activity (MSNA), mean arterial blood pressure (MAP) and heart rate (HR)) would be altered during mild orthostatic stress in ways that serve to limit orthostatic hypotension. ...
Seymour Roger S - - 2004
Changes in orientation in a gravitational field markedly alter the patterns of blood pressure and flow in animals, especially tall or long ones such as giraffes or snakes. Vertical orientation tends to reduce blood flow and pressure in the head for two major reasons. First, the increased vertical blood column ...
Hannerz Jan - - 2004
OBJECTIVE: To investigate the mechanisms behind the increase of chronic tension-type headache during head-down tilt. BACKGROUND: The pathophysiology of chronic tension-type headache is unknown. DESIGN AND METHODS: Ten patients suffering from chronic tension-type headache and 10 age- and sex-matched controls were studied with respect to pain intensity and alterations in ...
Cui Jian - - 2004
The purpose of this project was to test the hypothesis that increases in muscle sympathetic nerve activity (MSNA) during an orthostatic challenge is attenuated in heat-stressed individuals. To accomplish this objective, MSNA was measured during graded lower body negative pressure (LBNP) in nine subjects under normothermic and heat-stressed conditions. Progressive ...
Gotoh Taro Miyahara - - 2004
To examine acute hemodynamic responses to microgravity (microG) in the head, we measured carotid artery pressure (CAP) and jugular vein pressure (JVP) to calculate cephalic perfusion pressure (CPP = CAP - JVP) and recorded images of microvessels in the iris to evaluate capillary blood flow velocity (CBFV) and capillary diameter ...
Hachiya Tesshin - - 2004
INTRODUCTION: The present study was designed to determine how superficial blood distributed in the lower limb muscle during graded lower body negative pressure (LBNP). METHODS: Near-infrared spectroscopy (NIRS) was used to evaluate the blood volume change in the thigh muscles of seven volunteers during 35 min graded LBNP (rest, -10, ...
Longo Antonio - - 2004
PURPOSE: To evaluate the effect of posture change on subfoveal choroidal blood flow (ChBF) in normal volunteers. METHODS: The pulsatile, nonpulsatile, and mean ChBF were measured with laser Doppler flowmetry in 11 healthy volunteers with a mean age of 32 +/- 13 (SD) years. The posture of the subjects was ...
Czell David - - 2004
BACKGROUND: One problem in the mobilization of patients with neurological diseases, such as spinal cord injury, is the circulatory collapse that occurs while changing from supine to vertical position because of the missing venous pump due to paralyzed leg muscles. Therefore, a tilt table with integrated stepping device (tilt stepper) ...
Edlich Richard F - - 2004
During the last 40 years, there have been revolutionary advances in power wheelchairs. These unique wheelchair systems, designed for the physically immobile patient, have become extremely diversified, allowing the user to achieve different positions, including tilt, recline, and, more recently, passive standing. Because of this wide diversity of powered wheelchair ...
Wecht Jill M - - 2004
BACKGROUND: Arterial stiffness recently has been identified as an independent risk factor for cardiovascular disease. An accurate and noninvasive estimate of arterial stiffness can be made through close examination of the pulse wave contour, and is expressed as the augmentation index (AI). Increased stiffness is associated with increased systolic blood ...
Samniah Nemer - - 2004
AIMS: Normally, arterial baroreceptors attempt to minimize systemic hypotension by initiating reflex vasoconstriction and tachycardia. However, in the setting of vasovagal syncope (VVS), these usual compensatory mechanisms either fail to be triggered or the response is inadequate. We hypothesized that in VVS prone individuals, arterial baroreceptor response (BRR) is normal ...
Bosone Daniele - - 2004
The aim of this study was to evaluate, in a context of general inhibition of the sympathetic nervous system, the cerebral haemodynamic response to -30 degrees head-down tilt (HDT), a manoeuvre that produces an increase in intracranial arterial pressure. Nineteen healthy subjects were studied according to the following protocol: 10 ...
Durand S - - 2004
Previous studies suggest that skin surface cooling (SSC) preserves orthostatic tolerance; however, this hypothesis has not been experimentally tested. Thus the purpose of this project was to identify whether SSC improves orthostatic tolerance in otherwise normothermic individuals. Eight subjects underwent two presyncope limited graded lower-body negative pressure (LBNP) tolerance tests. ...
Ifuku Hirotoshi - - 2004
PURPOSE: The purpose of the present study was to compare cardiovascular responses in competitive swimmers with those in track and field (T and F) athletes during head-up tilt with engagement of the antigravity muscles in the lower extremities and during passive head-up suspension without the engagement of the antigravity muscles. ...
Cowie Dean A - - 2004
Symptoms of orthostatic intolerance are common after general anesthesia and are associated with an increased risk of postoperative morbidity. The contribution of orthostatic hypotension (OH) has not been well defined. We conducted a head-up tilt test on patients after general anesthesia for minor surgery to assess the incidence of and ...
Bradley John G - - 2003
Orthostatic hypotension is a physical finding defined by the American Autonomic Society and the American Academy of Neurology as a systolic blood pressure decrease of at least 20 mm Hg or a diastolic blood pressure decrease of at least 10 mm Hg within three minutes of standing. The condition, which ...
Zhang Y - - 2004
AIMS/HYPOTHESIS: Assessment of autonomic dysfunction provides prognostic data in diabetic patients. Clinical tests are limited to heart rate variability and blood pressure measurements. We investigated whether a detailed analysis of postural reflexes of patients during short-term head-up tilting and standing erect (both for 3 min) would provide useful clinical data. ...
Sun Xi-Qing - - 2003
The purpose of the present study was to investigate the changes of orthostatic tolerance and cardiac function during 21 d head-down tilt (HDT) bed rest and effect of lower body negative pressure in the first and the last week in humans. Twelve healthy male volunteers were exposed to -6 degrees ...
Yamazaki Fumio - - 2003
BACKGROUND: Heat stress induces a reduction of orthostatic tolerance. The cardiovascular responses, including the cardiac baroreflex response to heat stress, were examined to test the hypothesis that subjects with orthostatically low tolerance demonstrate an impaired baroreflex control of heart rate (HR) during heat stress. METHODS: There were 44 healthy young ...
Francis David T I - - 2003
The depth dependence of fish target strength has mostly eluded experimental investigation because of the need to distinguish it from depth-dependent behavioral effects, which may change the orientation distribution. The boundary-element method (BEM) offers an avenue of approach. Based on detailed morphometric data on 15 gadoid swimbladders, the BEM has ...
Sumiyoshi Masataka - - 2003
Isoproterenol is widely used as a provocative medium for vasovagal responses during tilt testing. Dose of isoproterenol infusion is generally titrated empirically by increase in resting heart rate before tilt up. To determine the optimal increase in resting heart rate with isoproterenol for tilt-induced vasovagal responses, we studied 97 consecutive ...
Kimmerly D S - - 2003
BACKGROUND: Cerebral vasoconstriction without concurrent changes in systemic arterial blood pressure has been observed in both normal individuals and those with idiopathic orthostatic intolerance following several minutes of postural stress when circulating catecholamines are elevated. Therefore, we tested the hypothesis that alpha-adrenergic activation with and without elevated circulating norepinephrine (NE) ...
Hisdal Jonny - - 2004
Previous studies have shown that the blood pressure response to isometric handgrip remains unchanged during reductions in preload induced by lower body negative pressure (LBNP). The purpose of the present study was to assess the beat-by-beat haemodynamic mechanisms allowing for precise control of mean arterial pressure (MAP). We have followed ...
Angeli Silvia - - 2003
Cardiovascular autonomic dysfunction can occur in Parkinson's disease (PD) and intracranial vascular modifications following orthostatism may be relevant to diagnostic and therapeutic decision-making. We performed transcranial Doppler monitoring of right middle cerebral artery (MCA) at rest and during passive 70 degrees tilt in 19 patients with idiopathic PD and in ...
Censi F - - 2003
The aim of this study is to evaluate the degree of coupling between the cardiovascular variability series and the respiration in subjects susceptible to neurally mediated syncope. Twenty-one informed patients susceptible to syncope and ten sex- and age-matched control subjects were enrolled in the study. ECG, respiration activity, and arterial ...
Bernardi Mauro - - 2003
BACKGROUND/AIMS: To clarify the hemodynamic pattern of pre-ascitic cirrhosis, we compared the impact of posture on systemic and regional hemodynamics of patients and healthy subjects without and with plasma volume expansion. METHODS: Cardiac index (CI), peripheral vascular resistance (PVRi), heart rate, mean arterial pressure, and the mean blood flow velocities ...
Rozenbaum Michael - - 2004
OBJECTIVE: The aim of this study was to assess the presence of dysautonomia, as manifested in abnormal cardiovascular reactivity, in patients with familial Mediterranean fever (FMF). METHODS: Fifty-five consecutive patients with FMF and 23 age- and sex-matched healthy controls were evaluated. Cardiovascular reactivity was studied: (1) using recordings of blood ...
LeLorier Paul - - 2003
INTRODUCTION: The combination of head-up tilt and incremental lower body negative pressure has shown promise in the diagnosis of orthostatic hypotension and neurocardiogenic syncope, although prior methodologies limited conclusions as to the reproducibility of the test. The aim of this study was to assess the efficacy and reproducibility of a ...
Harms Mark P M - - 2003
The activation of cardiovascular reflexes for postural adaptation questions whether, in healthy humans, the central blood volume is optimised to support the upright position. A functional definition of an 'optimal circulating volume' that provides the heart with enough central blood volume to establish a maximal cardiac output (CO) and mixed ...
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