Search Results
Results 501 - 550 of 1595
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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 ...
Bellard Elisabeth - - 2003
In patients with recurrent unexplained syncope, exaggerated peripheral venous pooling and impaired circulatory adjustment is thought to contribute to the outcome of a head-up tilt (HUT) test. The present study investigated the role of leg volume changes during venous congestion in the haemodynamic response of patients with recurrent unexplained syncope ...
Singer W - - 2003
BACKGROUND: Pharmacological treatment of orthostatic hypotension is often limited because of troublesome supine hypertension. OBJECTIVE: To investigate a novel approach to treatment using acetylcholinesterase inhibition, based on the theory that enhanced sympathetic ganglion transmission increases systemic resistance in proportion to orthostatic needs. DESIGN: Prospective open label single dose trial. MATERIAL: ...
Abdelmoneim Ismail - - 2003
To investigate the prevalence of possible hearing impairment and hypertension in long distance bus drivers compared to the city bus drivers in Abha city. This was a cross-sectional study involving 62 long distance bus drivers and 46 city bus drivers from October 2001 to March 2002. A specially-designed questionnaire was ...
Hisdal Jonny - - 2003
We have designed a lower body negative pressure (LBNP) chamber and control system that makes it possible to apply LBNP either very rapidly (< 300 ms), or more gradually, according to predefined protocols. The capability of the new, high-performance agile aircraft to reach a high-G onset rate makes it highly ...
Kaufmann Horacio - - 2003
BACKGROUND: In patients with neurogenic orthostatic hypotension (NOH), the availability of the sympathetic neurotransmitter norepinephrine (NE) in the synaptic cleft is insufficient to maintain blood pressure while in the standing posture. METHODS AND RESULTS: We determined the effect of oral administration of the synthetic amino acid L-threo-3,4-dihydroxyphenylserine (L-DOPS), which is ...
Rickards Caroline A - - 2003
The physiological differences between active and passive changes in posture have been previously established. This study determined the extent of the differences in the initial cardiovascular responses to the passive head-up tilt (HUT) and the active squat-stand test (SST). Eleven females and 13 males underwent one +75 degrees HUT and ...
Olsen H - - 2003
This study examined the influence of insulin and glucose on the transcapillary fluid absorption during lower body negative pressure (LBNP) in humans. Ten healthy males [23 (1) years] were exposed to LBNP of 45 cmH(2)O on two occasions: (1) before and during a hyperinsulinaemic clamp (HI) and (2) before and ...
Antonutto G - - 2003
Microgravity is an extreme environment inducing relevant adaptive changes in the human body, especially after prolonged periods of exposure. Since the early sixties, numerous studies on the effects of microgravity, during manned Space flights, have produced an increasing amount of information concerning its physiological effects, globally defined "deconditioning". Microgravity deconditioning ...
van Lieshout Johannes J - - 2003
The proper understanding of the cardiovascular mechanisms involved in complaints of short-lasting dizziness and the evaluation of unexplained recurrent syncope requires continuous monitoring of cardiac stroke volume (SV) in addition to blood pressure and heart rate. The primary aim of the present study was to evaluate a pulse wave analysis ...
Cui Jian - - 2003
To test the hypothesis that systemic inhibition of nitric oxide (NO) synthase does not alter the regulation of sympathetic outflow during head-up tilt in humans, in eight healthy subjects NO synthase was blocked by intravenous infusion of NG-monomethyl-L-arginine (L-NMMA). Blood pressure, heart rate, cardiac output, total peripheral resistance (TPR), and ...
Youde Jane - - 2003
OBJECTIVE: to assess the reproducibility of the cardiovascular responses to head-up tilt including cardiac output, stroke volume and peripheral resistance, in healthy older subjects using non-invasive methods. PARTICIPANTS: twenty-five healthy community-dwelling volunteers with a mean age of 69+/-3 years. METHODS: the subjects underwent head-up tilt table testing on two occasions ...
Kurihara Koichi - - 2003
Reflectance near-infrared spectroscopy (NIRS) has become a suitable and easily manageable method to monitor cerebral oxygenation changes in presyncopal and syncopal symptoms caused by postural changing or standing. A new clinical tissue oxygenation monitor has been recently developed which measures absolute tissue haemoglobin saturation (Tissue Oxygenation Index, TOI) utilizing spatially ...
Cron Thomas A - - 2003
Closed-loop stimulation (CLS) is a new sensor concept for rate adaptive pacing measuring changes in the unipolar right ventricular impedance, which correlates to changes of the right ventricular contractility and reflects the autonomic nervous innervation of the heart. Some patients do not tolerate the CLS mode because of inappropriate tachycardia, ...
Jacob Giris - - 2003
OBJECTIVE: Diabetic patients with incapacitating orthostatic hypotension can have either a "hyperadrenergic" or "hypoadrenergic" presentation. Although the latter is related to overt autonomic neuropathy, the former is proposed to be explained by appropriate autonomic responses. We hypothesize, however, that both conditions are part of a spectrum of autonomic dysfunction. RESEARCH ...
Perez Sondra A - - 2003
BACKGROUND: Many cardiovascular changes associated with spaceflight reduce the ability of the cardiovascular system to oppose gravity on return to Earth, leaving astronauts susceptible to orthostatic hypotension during re-entry and landing. Consequently, an anti-G suit was developed to protect arterial pressure during re-entry. A liquid cooling garment (LCG) was then ...
Hakeman Amy L - - 2003
Tolerance to positive vertical acceleration (Gz) gravitational stress is reduced when positive Gz stress is preceded by exposure to hypogravity, which is called the "push-pull effect." The purpose of this study was to test the hypothesis that baroreceptor reflexes contribute to the push-pull effect by augmenting the magnitude of simulated ...
Sheriff Don D - - 2003
The "push-pull" effect denotes the reduced tolerance to +Gz (hypergravity) when +Gz stress is preceded by exposure to hypogravity, i.e., fractional, zero, or negative Gz. Previous studies have implicated autonomic reflexes as a mechanism contributing to the push-pull effect. The purpose of this study was to test the hypothesis that ...
Jones A Y M - - 2003
BACKGROUND: Effect of gravity on heart rate and blood pressure are well documented but the effect of posture on R-wave amplitude has not been studied. AIM: To investigate the effect of posture on the heart rate (HR) and R-wave amplitude (RWA). METHODS: The electrocardiograph (ECG) was recorded in 20 young ...
Ogoh Shigehiko - - 2003
This investigation examined the interaction between carotid baroreflex (CBR) responsiveness during head-up tilt (HUT)-induced central hypovolaemia and aerobic fitness. Seven average fit (AF) individuals, with a mean maximal oxygen uptake (VO2max) of 49 +/- 1 (ml O2) kg-1 min-1, and seven high fit (HF) individuals, with a VO2max of 61 ...
Wasmund Stephen L - - 2003
The purpose of this study was to compare the hemodynamic and sympathetic nerve activity (SNA) responses to graded lower body negative pressure (LBNP) in healthy subjects with either a positive (n = 24, SNA in 8) or a negative (n = 18, SNA in 6) LBNP response. A positive LBNP ...
Shoemaker J Kevin - - 2003
The purpose of this study was to examine whether 14 days of head-down tilt bed rest (HDBR) alters autonomic regulation during Valsalva's manoeuvre (VM) and if this would predict blood pressure control during a 60 degrees head-up tilt (HUT) test. To examine autonomic control of blood pressure, we measured the ...
Jáuregui-Renaud Kathrine - - 2003
BACKGROUND: Clinical experience suggests that, through the control of heart rate, paced breathing may prevent syncope. OBJECTIVE: To assess the effect of metronome-paced breathing (0.2 Hz) on the outcome of head-up tilt test (HUT) in patients with vasovagal syncope. PATIENTS AND METHODS: Ten patients (two men), mean +/- SD age ...
Victorino Gregory P - - 2003
BACKGROUND: Tachycardia is believed to be closely associated with hypotension and is often listed as an important sign in the initial diagnosis of hemorrhagic shock, but the correlation between heart rate and hypotension remains unproved. STUDY DESIGN: Data were collected from all trauma patients, 16 to 49 years old, presenting ...
Lin Yuh-Feng - - 2003
BACKGROUND: The effects of midodrine on chronic hypotension in hemodialysis (HD) patients have not been well investigated. METHODS: We evaluated midodrine's effect on autonomic function and hemodynamics in 12 HD patients who had chronic systolic blood pressure less than 100 mm Hg. Midodrine (5.0 mg) twice a day was given ...
Karlsborg M - - 2003
Amyotrophic lateral sclerosis (ALS) is a severe, progressive disease affecting both the central and peripheral parts of the motor nervous system. Some studies have shown unequivocal indications of a more disseminated disease also affecting the autonomic nervous system. We therefore evaluated the centrally and peripherally mediated autonomic vascular reflexes by ...
Kamiya Atsunori - - 2003
Although orthostatic hypotension is a common clinical syndrome after spaceflight and its ground-based simulation model, 6 degrees head-down bed rest (HDBR), the pathophysiology remains unclear. The authors' hypothesis that a decrease in sympathetic nerve activity is the major pathophysiology underlying orthostatic hypotension after HDBR was tested in a study involving ...
Brown Clive M - - 2003
The aim of this study was to determine whether lower body negative pressure (LBNP), combined with noninvasive methods of assessing changes in systemic and cerebral vascular resistance, is suitable as a method for assessing cerebral autoregulation. In 13 subjects we continuously assessed heart rate, blood pressure, cerebral blood flow velocity ...
Julu P O O - - 2003
To study cardiovascular control in the period leading to vasovagal syncope we monitored beat-to-beat blood pressure, heart rate (HR) and forearm blood flow in 14 patients with posturally related syncope, from supine through to tilt-induced pre-syncope. Signals of arterial blood pressure (BP) from a Finapres photoplethysmograph and an electrocardiograph (ECG) ...
Eckberg D L - - 2003
AIM: Astronauts return to Earth with reduced red cell masses and hypovolaemia. Not surprisingly, when they stand, their heart rates may speed inordinately, their blood pressures may fall, and some may experience frank syncope. We studied autonomic function in six male astronauts (average +/- SEM age: 40 +/- 2 years) ...
Franchi Franco - - 2003
BACKGROUND: Defective baroreflex function has been suggested as a potential mechanism accounting for the development of syncopal episodes. The present study was therefore aimed at assessing the non-invasive, indirect hemodynamic profile and baroreflex function by means of tilting, which is a natural stimulation crucial to physiological baroreflex activity, in syncopal ...
Sundblad Patrik - - 2003
It has recently been shown that the phase relationship between respiration-induced changes in arterial pressure (AP) and heart rate (HR) are different in supine and upright postures. We wanted to further analyse the coupling between respiration, arterial blood pressure and HR in the time domain, and how this coupling was ...
Franke Warren D - - 2003
This study tested the hypotheses that trained swimmers would have greater orthostatic tolerance than runners and, if present, it would be due to differences in their autonomic and hemodynamic responses to graded central hypovolemia. Twenty intercollegiate male athletes [11 runners and 9 swimmers; .VO(2max) =70.0 (1.6) vs 69.5 (2.6) ml.kg(-1).min(-1), ...
Béchir Markus - - 2003
BACKGROUND: The interplay of resting muscle sympathetic nerve activity (MSA) and the baroreceptor reflex in patients with vasovagal syncope remains elusive. Hence, the aim of the present study was to investigate MSA, baroreceptor sensitivity, heart rate, and blood pressure under resting conditions and during orthostatic stress in patients with a ...
Journeay W Shane - - 2003
The hypothesis that reduced cardiac filling, as a result of lower body negative pressure (LBNP) and postexercise hypotension (PEH), would attenuate the reflex changes to heart rate (HR), skin blood flow (SkBF), and mean arterial pressure (MAP) normally induced by facial immersion was tested. The purpose of this study was ...
Perrault Hélène - - 2003
BACKGROUND: Tetralogy of Fallot (TOF) and its surgical repair are associated with alterations in right ventricular systolic and diastolic functions. The cardiopulmonary baroreflex describes the peripheral vasoconstriction response to the volume-unloading deactivation of left and possibly right ventricular receptors. Alterations in cardiac geometry or distensibility and pulmonary vasculature of operated ...
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