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At least 217 records · Page 12Linked to original sources
PubMed1995

Hemodynamic regulation during postural tilt assessed by heart rate- and blood-pressure variability combined with impedance cardiography.

Assessment of heart rate and heart rate variability (HRV) are used in sports medicine and space medicine to give conclusions about the functional state of the autonomic nervous system. Furthermore, reduced HRV and changed blood pressure variability (BPV) are accepted as risk factors in patients with cardiovascular diseases, metabolic syndrome and neurologic disorders. The aim of the first studies was to combine the evaluation of central hemodynamic (impedance cardiography) with HRV and BPV evaluation in the time and frequency domain (fft tracking) based on a standardized clinical test with automated protocol output. Data acquisition and -analysis was realized beat to beat (Kohto Ltd., Moscow) during forced breathing (150 s, 6 breath/min) and postural tilt (7 min, supine, transition to 55 degrees in 4 s, 7 min upright) allowing one to evaluate: orthostatic response type including impedance cardiography; activation of vagal afferences and efferences by forced breathing; vagal and sympathetic components during initial heart rate and blood pressure responses; characteristic changes of spectral balance of HRV and BPV (measured at the finger) during early regulation. First investigations on 34 normal volunteers subdivided into two age groups and on 13 patients with different diseases indicate that besides the age dependent changes (reduced HRV, reduced cardiac performance, reduced regulatory amplitudes and baroreflex sensitivity) individual response types can be described and dysfunction of different reflex loops can be detected. Consequently, the assessment of specific influences onto circulatory control by therapy, sport and rehabilitative training is possible and further studies are necessary.

Adult↗
PubMed1996

Is there an effective pharmacological treatment in the prevention of vasovagal syncope?

Many studies have claimed successful pharmacological prevention of vasovagal syncope in open formats with a wide variety of drugs. However, when therapy has been subjected to clinical trial to date no drug has shown any real benefit but it is necessary to add that the means of assessment leave much to be desired. These are repeat tilt testing, reported symptoms, analysis of syncopal burden in a population and time to syncopal recurrence. The disadvantages of any parameter derived from tilt testing is that its reproducibility is open to question and other aspects such as tilt duration before syncope have been inadequately investigated. With respect to symptom recurrence there are limitations because of the well known occurrence of vasovagal syncope in clusters and the long trial time that it is necessary because of relatively infrequent attacks. Furthermore, there is a placebo effect of the investigation of syncope which may delay the first recurrence. The first large trial is now underway and it is hoped that it may offer a method of prevention of vasovagal syncope which is both effective and acceptable.

Drug Evaluation↗
PubMed1996

Differences between syncope resulting from rapid onset acceleration and orthostatic stress.

BACKGROUND AND HYPOTHESIS: Orthostatically-induced syncope is accompanied by venous pooling and vasodilatation. Loss of consciousness during head-to-foot acceleration (G-LOC) in aviators may be caused by a different mechanism, as venous pooling should be prevented through the use of an anti-G suit. This research was conducted to test the hypothesis that in individuals wearing a well-fitted anti-G garment, no important changes occur in the volume of dependent regions during loss of consciousness resulting from rapid onset acceleration stress. Further, this work compares venous pooling patterns in G-LOC subjects to patterns seen during syncope in volunteers and patients subjected to orthostatic stress. We conducted the tilt/LBNP tests to establish what level of venous pooling was required to induce syncope in the absence of a hydrostatic component (other than 1 G) and to confirm that our equipment was sensitive enough to detect volume changes large enough to cause syncope. METHODS: Shifts in blood volume to the calf, thigh and abdominal segments were compared in subjects with G-LOC to those in subjects taken to presyncope with orthostatic stress created by upright tilt and lower body negative pressure (LBNP). Centrifuge subjects were exposed to a 15 s rapid onset (6 G.s-1) + 5 Gz exposure on the centrifuge while remaining relaxed and wearing a well-fitting anti-G suit, but with the anti-G suit pressure inactivated. RESULTS: Blood volume decreased an average of 14.9 +/- 22.1 ml in the calf segment; increased an average of 64.1 +/- 7.9 ml in the thigh segment, and decreased an average of 80.1 +/- 29.7 ml in the abdominal segment. The mean net change in volume of the three combined regions was not significantly different from zero. Presyncope was induced in subjects by a progressive exposure to upright tilt, and then addition of LBNP at -20 mm Hg and -40 mm Hg. In the tilt/LBNP group, there was a net increase of 1022 +/- 269.8 ml for the combined segments. Changes in all three segments were significantly different than the mean segmental volume changes seen in centrifuge subjects at G-LOC endpoints. Significant changes from baseline mean arterial pressure, but not heart rate were also seen within, but not between the 2 groups, with mean eye level blood pressures (ELBP) falling an average of 45.6 +/- 7.7 mm Hg in the tilt/LBNP group at syncope and 105.1 +/- 15.5 mm Hg in the centrifuge subjects at G-LOC. CONCLUSIONS: These differences suggest that G-LOC may be due entirely to hydrostatic effects, with venous pooling being prevented by the wearing of an ant-G garment, even when it remains uninflated.

Acceleration↗
PubMed1996

Effect of standing or walking on physiological changes induced by head down bed rest: implications for spaceflight.

BACKGROUND/HYPOTHESIS: To simulate exposure to microgravity and to determine the effectiveness of intermittent exposure to passive and active +1 Gz force (head-to-foot) in preventing head-down bed rest (HDBR) deconditioning, 4 d of 6 degrees HDBR were used. METHODS: Volunteers were 9 males, 30-50 yr, who performed periodic standing or controlled walking for 2 or 4 h.d-1 in 15-min bouts, one bout per hour, or remained in a continuous HDBR control condition (0 Gz). RESULTS: Standing 4 h (S4) completely prevented, and standing 2 h (S2) partially prevented, decreases in post-HDBR orthostatic tolerance (survival rates with 30 min of upright tilt at 60 degrees). Walking, both 2 h (W2) and 4 h (W4), and S4 attenuated decreases in peak oxygen uptake compared to 0 Gz. Compared to 0 Gz, both S4 and W4 attenuated plasma volume loss during HDBR. Urinary Ca2+ excretion increased over time with HDBR; the quadratic trend for urinary Ca2+, however, was attenuated with W2 and W4. CONCLUSIONS: We concluded that various physiological systems benefit differentially from passive +1 Gz or activity in +1 Gz and, in addition to the duration of the stimulus, the number of exposures to postural stimuli may be an important moderating factor.

Adult↗
PubMed1996

Cerebral hypoperfusion in orthostatic hypotension with globally denervated myocardium.

A 57-yr-old woman had frequent syncope when rising from a seated position. Her blood pressure fell from 140/80 mmHg to 60-70/40 mmHg while changing positions. Iodine-123-metaiodobenzylguanidine ([123I]MIBG) did not accumulate in the heart, whereas 201Tl-Cl (201Tl) did. Raise-up 99mTc-hexamethyl-propyleneamine oxime (99mTc-HMPAO) brain SPECT revealed decreased activity in the bilateral frontal areas, and subsequent supine 99mTc-HMPAO brain SPECT revealed filling in these areas, indicating that the cerebral blood flow (CBF) was transiently decreased in the frontal areas more than others in a standing position. The plasma norepinephrine (NE) level of this patient was normal during supine rest, but when she stood up, failure to increase the plasma level of NE uncovered a sympathetic nervous dysfunction. The CBF abnormality in patients with orthostatic hypotension may be due to a "functional" hemodynamic mechanism that induces orthostatic stress. This patient had transient hypoperfusion in the frontal areas when standing, without organic cerebral arterial stenosis. Only CBF in the frontal areas revealed relative hypoperfusion. These regions might be highly susceptible to a change in blood flow. The causes of orthostatic hypotension of this patient were autonomic failure with a disturbance of the sympathetic nerve endings, which was revealed by 99mTc-HMPAO brain SPECT and cardiac [123l]MIBG imaging.

3-Iodobenzylguanidine↗
PubMed1994

Combined head-up tilt and lower body suction: a test of orthostatic tolerance.

A combined tilt-table and lower body suction chamber to provide a progressive test of orthostatic tolerance which avoided the use of drugs and had a defined end point even in most asymptomatic subjects has been constructed and evaluated. An air-tight cover, sealed to a tilt-table and to the subject at the level of the iliac crest, was used to study the responses to: head-up tilting for 20 min, then tilting plus lower body suction at -20 and -40 mmHg for 10 min at each. Blood pressure, heart rate and cardiac output were measured noninvasively and orthostatic tolerance was assessed as the time to imminent onset of syncope. All subjects tolerated tilt alone but 84% developed signs and symptoms of presyncope during the suction. Younger women had a lower orthostatic tolerance than other groups. Values of the variables measured during tilting alone did not correlate with the measured orthostatic tolerance, but during the suction subjects who developed early syncope showed larger decreases in cardiac output and smaller maximal heart rates than the more resistant subjects. The test is repeatable and is likely to be of value in the assessment of orthostatic tolerance in patients and for evaluating the effects of various interventions.

Adult↗
PubMed1985

Orthostatic tolerance at different times of the day in physically average and very fit dayworkers.

We studied the relationship between the physical exercise capacity and the orthostatic tolerance of physically average fit and very fit dayworkers at different times of the day. Six male railroad workers were physically very fit and six were averagely fit (mean of the maximal oxygen consumption 57.4 and 34.6 ml.kg-1.min-1, respectively. The mean age was 32 years. The orthostatic tests were performed with a tilt-table at 2.00, 6.00, 10.00, 14.00, 18.00, and 22.00 hours on six different days. Orthostatic lability at night was seen in both groups. At 14.00 and 18.00 hours the orthostatic tolerance in average fit men was slightly lower than in very fit men. This difference in the orthostatic tolerance between the groups may be a sign of the interdependence of good exercise tolerance and orthostatic tolerance.

Adult↗
PubMed1976

Significance of daily rhythm for the interpretation of functional diagnostic procedures.

For the first time, the reaction of the cardiovascular system during day and night in young people was examined. We were mostly interested in the influence of the nervous system and any autonomic mechanism. We examined 20 subjects at 4-hour intervals on the ergometer (active exercise) and on the tilt-table (passive exercise) to find out the rhythm in the circulatory regulation. The test person was kept in vertical position on the tilt-table for 10 minutes. On the ergometer he had to perform a work-load of 100 Watt for 10 minutes. We measured pulse rate and blood pressure; we introduced new terms for the evaluation. "Orthostatic Index" and "Performance Index" will be further explained. The results were: A minimum in the orthostatic stability around 1 p.m. and 1--5 am, and a performance maximum at 1 p.m. and 5 p.m. Further details will be reported.

Blood Pressure↗
PubMed1990

Syncope: current diagnostic evaluation and management.

OBJECTIVE: To provide a comprehensive review of the causes, current diagnostic evaluation, and treatment of syncope. DATA IDENTIFICATION: New data and knowledge in this evolving field were critically analyzed by doing a MEDLINE search on syncope supplemented by selective review of English language literature citations in the Index Medicus before 1980. STUDY SELECTION: We reviewed approximately 200 published articles on syncope and closely related topics as well as using our own clinical experience. We selected articles if they addressed the pathophysiology of syncope, classification and causes, differential diagnosis, noninvasive and invasive evaluation, and current therapy. RESULTS OF DATA SYNTHESIS: Syncope is a common clinical problem, occurring in 30% to 50% of the adult population. The prognosis for syncope depends on its cause. Cardiac syncope has the worst prognosis and therefore mandates thorough evaluation and prompt treatment. Diagnostic evaluation is made difficult by the transient nature of the episodes and the many causes. Noninvasive testing reveals the cause of syncope in approximately 50% of cases. More extensive evaluation, including invasive electrophysiologic studies, has assumed a larger role in defining the cause of syncope in selected patients with structural heart disease in whom a noninvasive evaluation has been nondiagnostic. Recently tilt-table studies have been proposed as a clinically useful noninvasive test for vagally mediated syncope. CONCLUSIONS: A rational stepwise diagnostic and therapeutic approach to patients with syncope can be developed by initially doing a careful history and physical examination followed by a noninvasive evaluation and selective use of additional, more specialized or invasive tests. Future research should focus on defining the validity and utility of current diagnostic testing in syncope and on exploring further the pathophysiology of patients with recurrent, unexplained syncope.

Cardiovascular Diseases↗
PubMed1977

Case reports and studies of paraneoplastic hypotension: abnormal low pressure baroreceptor responses.

Intrathoracic stretch receptors regulate adjustments of the vasculature to gravitational changes and influence urinary water and solute excretion. Few reports of pathologic states involving interruption of these regulatory mechanisms have appeared. Two patients with orthostatic hypotenstion related to advanced intrathoracic carcinoma were studied, utilizing tilt-table examinations and immersion of the entire body in water to test the function of their intrathoracic baroreceptor reflex arcs. Both patients showed abnormalities of antidiuretic hormone level and sodium excretion as compared with normal controls. This suggests that total immersion is a safe and convenient test of the low-pressure baroreceptor system in patients with suspected dysfunction. Three patients are also reported whose charts were reviewed posthumously. Although they were not tested in the laboratory, their clinical data suggest that they too had been suffering from an interference with the transmission of impulses from the intrathoracic receptors.

Adult↗
PubMed1991

Transcranial Doppler evaluation of syncope: an application in aerospace physiology.

A non-invasive method which combines the simultaneous measurement of mean arterial blood pressure (MBP), heart rate (HR) and mean cerebral blood flow velocity (MFV) was used to monitor patients with history of syncope, in horizontal and vertical posture tilt at 80 degrees. MFV in the right middle cerebral artery was measured using a transcranial Doppler instrument (TCD). MFV decreased concurrently with the onset of symptoms, and at the time of syncope reached an average of 68% below pre-tilt values. At the same time MBP showed an average decline of 25%, and HR increased by 38%. There was no correlation between MBP and MFV, at the onset of tilt, presyncope and syncope. MFV, but not HR or MBP, showed significant transition from one condition to the other. These data suggest that there may be a useful application of TCD measurements of MFV in aeromedical evaluation of syncope or syncopal tendency. These measurements would necessarily be used in conjunction with a tilt-table procedure. The possibility exists that MFV might be useful to preclude the actual occurrence of syncope in test subjects, or to show an abnormal tendency toward syncope, but will require more extensive testing than that carried out in the present study.

Adult↗
PubMed1990

[Vestibular ataxia caused by meningeal carcinomatosis].

A 74-year-old man developed progressive deafness and unsteady gait two years after gastrectomy for a gastric cancer. Neurological examination revealed an alert and intelligent Japanese male in no acute distress. The optic fundi were normal. The pupils and the extraocular muscles were normal, however, horizontal nystagmus was noted in right and left gaze. He showed marked bilateral deafness, and loss of caloric response bilaterally. No muscle atrophy nor weakness was noted. His gait was wide-based and ataxic. Tandem gait was impossible. Romberg sign was present. No cerebellar ataxia was noted in the finger-to-nose or the heel-to-knee test. No adiadochokinesis was noted. Hyperextensibility was noted in the lower extremities. Deep reflexes were normal in the upper limbs, and diminished in the lower extremities. Sensation was intact. He showed the jumbling phenomenon, and the disturbance of the righting reflex in the tilt-table examination. Neuroradiological as well as laboratory studies were unremarkable except for the high titer of CEA in the CSF. Four months after his admission, malignant tumor cells were found in the CSF. It seemed likely that he had completely lost bilateral vestibular and auditory functions caused by meningeal carcinomatosis. His disturbance of gait and station was apparently similar to cerebellar ataxic gait, however, he did not have limb ataxia. The cranial CT scans failed to show cerebellar atrophy. It was our impression that his motor disturbance was in all likelihood caused by the bilateral loss of vestibular functions, i.e., vestibular ataxia.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1981

Evaluation of the effects of muscle stretch and weight load in patients with spastic paraplegia.

Clinical observations on patients with spastic paraplegia have indicated that a training regime including weight load on the lower limbs may reduce the muscular hypertonus. Due to the spontaneous fluctuations and great variability in muscle tone it is difficult to judge from clinical findings how the effects may be related to muscle stretch and weight load. Therefore, quantitative determination of the effects on muscle tone by stretch and loading was made in 9 paraplegic patients. Muscle tone was measured before and after 30 min of stretch or weight load in 8 sessions on 4 consecutive days. Stretch was obtained by bracing the foot in maximal dorsal flexion with patient in supine position. For weight load on the lower limbs, the patient stood on a tilt-table at an angle of 85 degrees with feet in 15 degrees dorsal or plantar flexion. Resistance to passive movements was determined during a series of sinusoidal ankle joint movements at three different speeds. After weight load in standing with the feet in dorsal or plantar flexion, the average reduction was 32 and 26%, respectively. After stretch in supine, the average reduction was 17%. Thus, the three procedures tested all resulted in reduction of muscle tone. The largest reductions were obtained by weight load with stretch imposed upon the calf muscles.

Adult↗
PubMed1991

Effects of a single session of prolonged plantarflexor stretch on muscle activations during gait in spastic cerebral palsy.

Activations of the triceps surae (TS) and tibialis anterior (TA) muscles during gait were studied in children with spastic cerebral palsy (CP) immediately before and after 30 min of standing on a tilt-table with the ankle dorsiflexed to stretch the TS in the experimental group (n = 8) or after a rest period in the control group (n = 11). The EMG activity from the TS and TA was recorded concomitantly with electronic footswitch signals by a computer. Video records were made of the sagittal gait movements. Effects of PMS were determined by comparing change scores for selected spatiotemporal and muscle activation parameters between the groups. The change scores defined for the muscle activations were: a post-test/pre-test ratio of the EMG activity in specific segments of the gait cycle and a locomotor spasticity index. PMS did not significantly (p greater than 0.05) affect any of the spatiotemporal parameters nor did it alter any of the TS and most of the TA activation parameters or the SI indexes for the TS and TA. Only the TA post/pre activation ratio for the 0-16% segment of the gait cycle was smaller (p less than 0.01), indicating a decrease in TA activation post-PMS.

Adolescent↗