Search Results
Results 601 - 650 of 1579
< 8 9 10 11 12 13 14 15 16 17 18 >
Kimmerly Derek S - - 2002
Humans exposed to real or simulated microgravity experience decrements in blood pressure regulation during orthostatic stress that may be related to autonomic dysregulation and/or hypovolemia. We examined the hypothesis that hypovolemia, without the deconditioning effects of bed rest or spaceflight, would augment the sympathoneural and vasomotor response to graded orthostatic ...
Loke G P Y - - 2002
Forty women presenting for elective Caesarean section under spinal anaesthesia were randomly assigned to have anaesthesia induced in the right lateral position either in the horizontal position or with 10 degrees head-up tilt. Hyperbaric bupivacaine 2 ml 0.5% with 0.1 mg of morphine was injected intrathecally before the parturients were ...
Peterson Kristy - - 2002
A numerical model of the cardiovascular system was used to quantify the influences on cardiac function of intrathoracic pressure and intravascular and intraventricular hydrostatic pressure, which are fundamental biomechanical stimuli for orthostatic response. The model included a detailed arterial circulation with lumped parameter models of the atria, ventricles, pulmonary circulation, ...
Schroeder Christoph - - 2002
BACKGROUND: Observations in patients with functional mutations of the norepinephrine transporter (NET) gene suggest that impaired norepinephrine uptake may contribute to idiopathic orthostatic intolerance. METHODS AND RESULTS: We studied the effect of the selective NET blocker reboxetine and placebo in a randomized, double-blind, crossover fashion on cardiovascular responses to cold ...
Pitzalis Mariavittoria - - 2002
BACKGROUND: Asymptomatic reductions in arterial pressure have been reported to occur before the onset of tilt-induced syncope. We investigated the predictive value of these reductions for a positive tilt result. METHODS AND RESULTS: In a first study, 238 consecutive healthy subjects with unexplained syncope underwent a passive tilt table test. ...
Suzuki Takashi - - 2002
PURPOSE: Our purpose was to examine perioperative alterations in hemodynamic changes with head-up tilt (HUT) in patients undergoing endoscopic thoracic sympathectomy (ETS). METHODS: The subjects were 11 patients with essential hyperhidrosis scheduled to undergo ETS (ETS group) and 9 age-matched volunteers undergoing minor surgery (control group). HUT was performed (40 ...
Rees S G O - - 2002
Sixty healthy women undergoing elective Caesarean section were randomly allocated to either a measured 15 degrees left table tilt position (n = 31) or full left lateral position (n = 29) for a 15-min period after spinal blockade. Arm and leg blood pressure, ephedrine requirements, symptoms, fetal heart rate, cord ...
Cavalcanti Silvio - - 2002
BACKGROUND: A large inter-subject variability exists in the arterial pressure response to hemodialysis-induced blood volume (BV) withdrawal. We investigated the hypothesis that this variability is due to the inter-subject differences in the short-term reflex capacity to compensate for hypovolemia. METHODS: Mean arterial pressure (MAP), heart rate (HR) and the percentage ...
Prisk G Kim - - 2002
BACKGROUND: Head-down tilt (HDT) of 6 degrees is a commonly used model of weightlessness, but there are few comparisons with actual microgravity. HYPOTHESIS: Our study was designed to prove that the changes in cardiopulmonary function seen in HDT would be similar to those seen in microgravity. METHODS: We compared measurements ...
Yalcin Ahmet U─čur - - 2002
BACKGROUND: Recently some pathogenetic parallels have been drawn between dialysis-induced hypotension and disorders characterized by hemodynamic instability due to autonomic dysfunction, such as neurocardiogenic syncope and idiopathic orthostatic hypotension. Several studies have shown that central serotonergic pathways participate in the abnormal response, and selective serotonin reuptake inhibitors improve the symptoms ...
Vijayalakshmi P - - 2002
Time course of systolic time interval (STI) variations during 60 degrees head-up tilt (HUT) was studied in 21 patients with essential hypertension and equal number of age-matched control subjects. ECG, Phonocardiogram and carotid pulse were recorded simultaneously on polygraph. Electromechanical systole (QS2), left ventricular ejection time (LVET), pre ejection period ...
Nakajima Yasufumi - - 2002
Thermoregulation interacts with cardiovascular regulation within the central nervous system. We therefore evaluated the effects of head-down tilt on intraoperative thermal and cardiovascular regulation. Thirty-two patients undergoing lower-abdominal surgery were randomly assigned to the 1) supine, 2) 15 degrees -20 degrees head-down tilt, 3) leg-up, or 4) combination of leg-up ...
Ertl Andrew C - - 2002
Astronauts returning from space have reduced red blood cell masses, hypovolaemia and orthostatic intolerance, marked by greater cardio-acceleration during standing than before spaceflight, and in some, orthostatic hypotension and presyncope. Adaptation of the sympathetic nervous system occurring during spaceflight may be responsible for these postflight alterations. We tested the hypotheses ...
Shiraishi Makoto - - 2002
The hypothesis was tested that acute water immersion to the neck (WI) compared with 6 degrees head-down tilt (HDT) induces a more pronounced distension of the heart and lower plasma levels of vasoconstrictor hormones. Ten healthy males underwent 30 min of HDT, WI, and a seated control (randomized). During WI, ...
Arbeille P - - 2001
The objective of this investigation was to identify the major cardiovascular changes induced by exposure to real or simulated Og (spaceflights: 6, 14, 21 and 25 days, and 6 months; head down tilt, HDT: 10 h, 4, 5, 7, 30 and 42 days), with a minimum of counter-measures. The following ...
Kawanokuchi J - - 2001
To clarify the response of muscle sympathetic nerve activity (MSNA) to static stimulation of otolith organs in a craniocaudal direction (+Gz) in humans, we examined the effect of otolith stimulation on MSNA without changing the effect of cardiopulmonary baroreceptors using a 6-8.5 degrees head-down tilt (HDT) and lower body negative ...
Fulco C S - - 2001
BACKGROUND: Increased blood level of norepinephrine, a primary alpha-adrenergic agonist, is associated with high-altitude exposure, and may help regulate key physiological functions (e.g., blood pressure). We hypothesized that blocking alpha1-adrenergic receptors would impair circulatory compensation for an orthostatic challenge to a greater extent at altitude than at sea level. METHODS: ...
Omboni S - - 2001
In the present study, we have assessed in patients with neurogenic orthostatic hypotension the haemodynamics underlying the reduced tolerance to standing after prolonged recumbency at night. In 10 patients with neurogenic orthostatic hypotension (age 33-68 years), of which seven were being treated with fludrocortisone and/or sleeping in the 12 degrees ...
Convertino V A - - 2001
We measured central venous pressure (CVP); plasma volume (PV); urine volume rate (UVR); renal excretion of sodium (UNa); and renal clearances of creatinine, sodium, and osmolality before and after acute volume infusion to test the hypothesis that exposure to microgravity causes resetting of the CVP operating point. Six rhesus monkeys ...
Convertino V A - - 2001
Lower body negative pressure (LBNP) has been extensively used for decades in aerospace physiological research as a tool to investigate cardiovascular mechanisms that are associated with or underlie performance in aerospace and military environments. In comparison with clinical stand and tilt tests, LBNP represents a relatively safe methodology for inducing ...
Faghri P D - - 2001
OBJECTIVE: To evaluate the effects of functional electric stimulation (FES) of lower limb muscles during 30 minutes of upright standing on the central and peripheral hemodynamic response in persons with spinal cord injury (SCI). DESIGN: A repeated-measure design. Subjects were used as their own control and underwent 2 testing protocols ...
Shoemaker J K - - 2001
We tested the hypothesis that differences in sympathetic reflex responses to head-up tilt (HUT) between males (n = 9) and females (n = 8) were associated with decrements in postural vasomotor responses in women. Muscle sympathetic nerve activity (MSNA; microneurography), heart rate, stroke volume (SV; Doppler), and blood pressure (Finapres) ...
Hermosillo A G - - 2001
Upright posture requires rapid and effective circulatory and neurologic compensations to maintain blood pressure and consciousness. Although it has been recognized over the past 100 years or more that the act of standing may cause hypotension in patients with autonomic dysfunction, only recently several of the pathophysiologic mechanisms resulting in ...
Blaber A P - - 2001
INTRODUCTION: The partial pressure of end tidal CO2 (PetCO2) is known to decrease with head-up tilt. Decreases in arterial CO2 reduce cerebral blood flow (CBF) and may increase the incidence of presyncope. We measured cerebral and central cardiovascular responses to repeated tilt where: 1) PetCO2 was allowed to change with ...
Evans J M - - 2001
Healthy young people may become syncopal during standing, head up tilt (HUT) or lower body negative pressure (LBNP). To evaluate why this happens we measured hormonal indices of autonomic activity along with arterial pressure (AP), heart rate (HR), stroke volume (SV), cardiac output (CO), total peripheral resistance (TPR) and measures ...
Singh K - - 2001
One of the pathophysiological features in Buerger's disease, i.e. thromboangitis obliterans (TAO), is vasospastic phenomena. So autonomic reactivity was evaluated in 12 patients of Buerger's disease (1-6 years duration) and compared to age and sex matched controls (nonsmokers). Basal heart rate was significantly (P < 0.001) higher without any variation ...
Potocka-Plazak K - - 2001
Orthostatic hypotension is common in the elderly and could be the cause of impaired vision, dizziness, fainting spells and falls. To date, studies on orthostatic hypotension have chiefly concentrated on elderly patients in nursing homes, outpatients or healthy subjects. Congestive heart failure (CHF) is one of the most common causes ...
Carey B J - - 2001
The cerebrovascular changes that occur prior to vasovagal syncope (VVS) are unclear, with both increases and decreases in cerebrovascular resistance being reported during pre-syncope. This study assessed the cerebrovascular responses, and their potential underlying mechanisms, that occurred before VVS induced by head-up tilt (HUT). Groups of 65 normal subjects with ...
Mano T - - 2001
Muscle sympathetic nerve activity (MSNA) can be directly recorded from human peripheral nerves in situ using microneurography. MSNA plays an essential role to control systemic blood pressure against gravitational stress. MSNA was enhanced by changing posture against terrestrial gravity from lying to sitting, and from sitting to standing. This activity ...
Panton L B - - 2001
The purpose of the present study was to determine whether resistance training alters the cardiovascular responses to submaximal lower body negative pressure (LBNP) in the elderly. Twenty-one subjects were randomized into a control (C: n=10; 70 +/- 3 years, mean +/- SD) or a resistance training (TR: n=11; 67 +/- ...
Regnard J - - 2001
Many studies have used water immersion and head-down bed rest as experimental models to simulate responses to microgravity. However, some data collected during space missions are at variance or in contrast with observations collected from experimental models. These discrepancies could reflect incomplete knowledge of the characteristics inherent to each model. ...
Shoemaker J K - - 2001
Arterial hypocapnia has been associated with orthostatic intolerance. Therefore, we tested the hypothesis that hypocapnia may be detrimental to increases in muscle sympathetic nerve activity (MSNA) and total peripheral resistance (TPR) during head-up tilt (HUT). Ventilation was increased approximately 1.5 times above baseline for each of three conditions, whereas end-tidal ...
Cooper V L - - 2001
Orthostatic stress, including standing, head-up tilting and lower body suction, results in increases in peripheral vascular resistance but little or no change in mean arterial pressure. This study was undertaken to determine whether the sensitivity of the carotid baroreceptor reflex was enhanced during conditions of decreased venous return. We studied ...
Carey B J - - 2001
BACKGROUND: The effect of orthostatic stress on dynamic cerebral autoregulation (CA) in normal subjects and patients with recurrent vasovagal syncope (VVS) is unclear. This study assessed the dynamic CA responses of both groups to head-up tilt. METHODS AND RESULTS: Seventeen patients with recurrent VVS and 17 pair-matched control subjects underwent ...
Pagani M - - 2001
The haemodynamic and autonomic effects of prolonged exposure to simulated microgravity were assessed non-invasively in seven healthy volunteers completing a 42-day -6 degrees head down tilt. Before, during and after head down tilt, subjects were exposed to moderate excitatory stimuli (mental arithmetic and static handgrip) to gauge possible progressive impairment ...
Pavy-Le Traon A - - 2001
Thigh cuffs are used by Russian cosmonauts to limit the fluid shift induced by space flight. A ground simulation using the head-down bed rest (HDBR) model was performed to assess the effects of thigh cuffs on clinical tolerance and orthostatic adaptation. 8 male healthy volunteers (32.4 +/- 1.9 years) participated ...
Sato J - - 2001
We studied dynamic cerebrovascular responses in eight healthy humans during repetitive stepwise upward tilt (SUT) and stepwise downward tilt (SDT) maneuvers between supine and 70 degrees standing at intervals of 60 s. Mean cerebral blood flow velocity (FV(MCA)) was measured at the middle cerebral artery (MCA) with transcranial Doppler ultrasonography. ...
Yamazaki F - - 2001
The purpose of this study was to elucidate the effect of raised body temperature per se during acute heat stress on the spontaneous arterial baroreflex control of heart rate (fc) in humans. To investigate whether unloading of cardiopulmonary baroreceptors during whole-body heating would alter the arterial baroreflex control of fc, ...
Aljuri A N - - 2001
Prolonged exposure to microgravity in space flight missions (days) impairs the mechanisms responsible for defense of arterial blood pressure (ABP) and cardiac output (CO) against orthostatic stress in the post-flight period. The mechanisms responsible for the observed orthostatic intolerance are not yet completely understood. Additionally, effective counter measures to attenuate ...
Hisdal J - - 2001
The hypothesis tested was that there are significant transient changes in the cardiovascular variables after rapid onset and release of mild lower body negative pressure (LBNP, -20 mmHg), even in experimental situations where there is no detectable change in steady-state values. Twelve subjects participated in the study. Heart rate, stroke ...
Takase B - - 2001
INTRODUCTION: A reduction in left ventricular volume and an increase in epinephrine levels have been reported in tilt-induced neurally mediated syncope. To compare the mechanisms of isoproterenol-induced and nitroglycerin-induced syncope during head-up tilt and to investigate the role of catecholamines, the temporal changes in plasma levels of norepinephrine and epinephrine ...
Spaak J - - 2001
We hypothesized that impaired cardiovascular responses to isometric muscle action contribute to the cardiovascular deconditioning that occurs after space flight (SF) and head-down-tilt bed rest (HDT). Six subjects were studied before, during and after 120 days of -6 degrees HDT, and four subjects were studied before, during (two subjects) and ...
Magnifico F - - 2001
Metoclopramide (MCP), a central and peripheral dopaminergic blocker with cholinergic activity, has been proposed to treat orthostatic hypotension (OH) on the basis that it could antagonize the vasodilator and natriuretic effects of dopamine. The authors evaluated cardiovascular responses to MCP in 11 subjects with OH: 6 with multiple system atrophy ...
Guézennec C Y - - 2001
Oxygen consumption (VO2) and blood pressure regulation were measured on five pilots during and after normal training aerobatics flights of a mean duration of 35 min. The acceleration vector along the longitudinal axis of the body (Gz) ranged from + 6.5 Gz to -3.5 Gz. VO2 was continuously monitored by ...
Rhea, Lynn P.
On of the age-related changes associated with normal aging is the inability to maintain normal blood pressure homeostasis, a common clinical condition known as orthostatic intolerance. There are little data on the effects of strength training in healthy adults and orthostatic intolerance, and only one study on strength training and ...
van Hoeyweghen R - - 2001
Lower body negative pressure (LBNP) reduces central venous pressure (CVP) and cardiac output. The elderly are reported to have a limited capacity to increase cardiac output by increasing heart rate (HR), are especially dependent on end diastolic volume to maintain stroke volume and therefore should be especially vulnerable to LBNP. ...
de Visser E - - 2001
OBJECTIVE: Evaluation of the changes in balance control observed in patients after limb-saving surgery for malignant tumors of the lower limb. DESIGN: Case series. RESULTS: In 11 patients who underwent limb-saving surgery and 10 healthy, age-matched controls, displacement of the amplitude of the center of pressure (ACP) and velocity of ...
Perhonen M A - - 2001
BACKGROUND: Orthostatic intolerance after bed rest is characterized by hypovolemia and an excessive reduction in stroke volume (SV) in the upright position. We studied whether the reduction in SV is due to a specific adaptation of the heart to head-down tilt bed rest (HDTBR) or acute hypovolemia alone. METHODS AND ...
Patel A R - - 2001
Lower body negative pressure (LBNP) may provide an alternative test of cardiovascular autonomic function for patients unable to perform the Valsalva maneuver (VM). LBNP at -40 mmHg for 30 s was compared to the VM at 40 mmHg for 15 s with heart rate and blood pressure measured continuously in ...
Capderou A - - 2001
BACKGROUND/HYPOTHESIS: During parabolic flight, in the standing position, changes are partly due to an acute shift in fluid between the lower extremities, the head and the thorax (Vaïda P, et al. J Appl Physiol 1997; 82:1091-7; and Bailliart O, et al. J Appl Physiol 1998; 85:2100-5). We hypothesized that modifications ...
< 8 9 10 11 12 13 14 15 16 17 18 >