Search Results
Results 601 - 650 of 1604
< 8 9 10 11 12 13 14 15 16 17 18 >
Shoemaker J K - - 2002
Sympathetic outflow increases during head-up tilt (HUT) to stabilize blood pressure in the presence of decreases in venous return and stroke volume (SV). Otherwise, orthostatic hypotension would develop. Gender differences in orthostatic tolerance have been noted but the mechanisms are still uncertain. More recently, Waters et al. reported in a ...
Krishnan Anita - - 2002
Perfimttion of the tympanic membrane is nature's may of maintaining the middle far vntilation under the pressure of inflammatory process in the tempanomastoid cleft. An attempt at reconstruction with the possibility of infection lurking in and around the mastoid air cells may seem futile. Vow the quntinn arises as to ...
Baisch Friedhelm J - - 2002
In 1951 Gauer, Henry and Sieker proposed that "central hyper-volemia" might produce a diuresis that serves to reduce blood volume, a postulated negative-feedback system for the control of blood volume. Recent surprising results from human spaceflight indicate that although a central hyper-volemia takes place in weightlessness, an increase in salt ...
Hinghofer-Szalkay H - - 2002
This study was undertaken to identify combinations ('neutral points', NP) of orthostatic (tilt: head-down = HDT, head-up = HUT) and pseudo-orthostatic (lower body pressure: positive = LBPP, negative = LBNP) stimuli able to compensate one another in their effect on hemodynamic variables, electrical thoracic impedance (TI), hematocrit and plasma mass ...
Convertino Victor A - - 2002
Head-up tilt table experiments conducted in astronauts prior to and immediately after the NASA Neurolab Space Mission (STS-90) revealed that a reduction in stroke volume induced by moving from the supine to upright posture was associated with increased muscle sympathetic nerve activity (MSNA). Although this finding was not unexpected, lower ...
Holmes M J MJ Department of Otolaryngology, University of Pittsburgh, Eye and Ear Institute, Room 106, 203 Lothrop Street, Pittsburgh, PA 15213, - - 2002
The vestibular system is known to participate in cardiovascular regulation during movement and postural alterations. The present study considered whether lesions of two regions of the posterior cerebellar vermis (the nodulus and uvula) that provide inputs to vestibular nucleus regions that affect control of blood pressure would alter cardiovascular responses ...
Hisdal Jonny - - 2002
Mild (0 to -20 mmHg) lower body negative pressure (LBNP) has traditionally been considered to elicit reflex responses mediated by cardiopulmonary baroreceptors only, without any arterial baroreflex involvement. Mild LBNP has therefore frequently been used to study the influence of cardiopulmonary baroreceptors on the human circulatory system. In a previous ...
Stewart Julian M - - 2002
BACKGROUND: Orthostatic intolerance is characterized by postural tachycardia syndrome (POTS) with exaggerated tachycardia, orthostatic symptoms, and "pooling" (which comprises acrocyanosis and dependent edema when upright). My colleagues and I tested the hypothesis that pooling results from increased venous compliance in POTS patients. METHODS AND RESULTS: Fifteen patients aged 13 to ...
Chandler Margaret P - - 2002
Continuous haemodynamic responses to head-up tilt (HUT) and its reversal were studied in 21 subjects with sympathetic denervation due to primary chronic autonomic failure; 10 had pure autonomic failure (PAF; peripheral failure) and 11 had multiple system atrophy (MSA; central failure); 8 healthy subjects (controls) also were studied. Supine systolic, ...
Harada Chizuru C Oita Medical University, School of Nursing, Hasama, Japan. - - 2002
This pilot study was undertaken to determine the effects of a 10-degree leg elevation for 30-degree head-up position on body displacement and sacral interface pressure for 2 hours. The study used a comparative, quasi-experimental design with repeated measures. A convenience sample of 10 healthy Japanese women was used. Body displacement ...
Tsutsui Yuka - - 2002
BACKGROUND: It is warranted to test the hypothesis that the orthostatic tolerance does not diminish in the aging process per se in healthy individuals. OBJECTIVE: The purpose of the present study was to examine the effects of aging on cardiovascular response and baroreflex sensitivity during lower body negative pressure (LBNP) ...
Vloet Lilian C M - - 2002
OBJECTIVES: orthostatic hypotension is a common and potentially dangerous condition in elderly patients, often accompanied by dizziness and falls. To diagnose orthostatic hypotension, many physicians rely on blood pressure measurements performed by nurses. DESIGN: observational and descriptive study. SETTING: departments of Internal Medicine, Geriatric Medicine, and Surgery in eight hospitals ...
Jardine D L - - 2002
The importance of cardiac output (CO) to blood pressure level during vasovagal syncope is unknown. We measured thermodilution CO, mean blood pressure (MBP), and leg muscle mean sympathetic nerve activity (MSNA) each minute during 60 degrees head-up tilt in 26 patients with recurrent syncope. Eight patients tolerated tilt (TT) for ...
Hilz M J - - 2002
OBJECTIVE: Cerebral autoregulation was assessed by transcranial Doppler sonography in 10 patients with familial dysautonomia and 10 age matched controls. METHODS: Blood pressure, heart rate, and middle cerebral artery blood flow velocity (CBFV) were simultaneously recorded when supine and during 180 seconds of head up tilt. Cerebrovascular resistance (CVR) was ...
Heitterachi Edward - - 2002
BACKGROUND: orthostatic hypotension may be an important risk factor for falls, though this has not yet been demonstrated in prospective studies. This may be because conventional methods of measuring blood pressure changes are too imprecise and not optimally timed. OBJECTIVES: to determine whether changes in blood pressure induced by upright ...
Mathias Christopher J - - 2002
A fundamental human expectation is to stand upright. This exposes the cardiovascular system to gravitational forces, with a fall in pressure above heart level exposing organs such as the brain to impaired perfusion if adequate adaptive mechanisms are not activated. The autonomic nervous system plays an important role in the ...
Mukai Seiji - - 2002
A common problem among elderly people, orthostatic hypotension is associated with significant morbidity and mortality, which may be caused by medications, the cumulative effects of age- and hypertension-related alterations in blood pressure regulation, or age-associated diseases that impair autonomic function. Evaluation requires multiple blood pressure measurements taken at different times ...
Vaitl Dieter - - 2002
This article examines the relation between the perception of one's own body position and the distribution of fluid along the subject's spinal (z-) axis. Two experiments are reported. The first one is a replication of the Vaitl et al. study [J. Psychophysiol. 27 (1997) 99] which has shown that changes ...
Toska Karin - - 2002
Mechanisms involved in the control of arterial pressure during postural changes were studied by analysis of the dynamic time course of cardiovascular changes during head-up tilt (HUT) and tilt back to supine position (TB). Beat-to-beat values of cardiovascular variables were recorded continuously before, during, and after passive HUT to 30 ...
Yamasaki Masao - - 2002
To clarify the effects of the head-down tilt (HDT) posture on the postnatal development of the aortic baroreflex, we raised rabbits from 3-4 weeks of age for 34-36 d in this posture, which simulates the headward shift of body fluid in space, and examined the structural and functional characteristics of ...
Faber J - - 2002
In hypothyroidism, lack of thyroid hormones results in reduced cardiac function (cardiac output [CO]), and an increase of systemic vascular resistance (SVR). We speculated whether hemodynamic regulation in subjects with subclinical hypothyroidism (SH) (defined as mildly elevated thyrotropin [TSH] despite free thyroxine [T(4)] and triiodothyronine [T(3)] estimates within reference range) ...
Shannon John R - - 2002
PURPOSE: Water drinking increases blood pressure in a substantial proportion of patients who have severe orthostatic hypotension due to autonomic failure. We tested the hypothesis that water drinking can be used as a practical treatment for patients with orthostatic and postprandial hypotension, as well as those with orthostatic tachycardia. SUBJECTS ...
Hofer C K - - 2002
BACKGROUND: It is still controversial whether elevated cardiac filling pressures after the onset of pneumoperitoneum are the consequence of increased intrathoracic pressure or of increased venous return. The aim of this study was to assess the effects of pneumoperitoneum and body positioning on intrathoracic blood volume (ITBV). METHODS: Thirty anesthetized ...
Jordan Jens - - 2002
Orthostatic hypotension is seen in various medical conditions. It can be secondary to medications or volume depletion. It can also be due to autonomic neuropathy secondary to other diseases, such as diabetes mellitus, or to primary degenerative processes of the autonomic nervous system. Orthostatic hypotension dominates the clinical picture of ...
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, ...
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 ...
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. ...
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 ...
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 ...
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 ...
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 ...
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, ...
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 ...
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 ...
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 ...
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 ...
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 ...
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: ...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
< 8 9 10 11 12 13 14 15 16 17 18 >