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Biomedical subjects

A Güell

Publications and source records attributed to A Güell.

17 recordsLinked to original sources
PubMed1992

Balance and gait analysis after 30 days -6 degrees bed rest: influence of lower-body negative-pressure sessions.

Five volunteers took part in -6 degrees head-down bed-rest experiments for 30 d. In the first experiment, three subjects underwent several sessions of lower-body negative-pressure (LBNP) per day, with two others serving as controls. In the second, the LBNP group of the first experiment became the control and vice versa. Two experimental protocols analyzed the bed-rest-induced modifications of balance and gait and the efficiency of LBNP in counteracting these modifications. A kymographic method allowed the measurement of walking parameters. Anteroposterior and lateral sways were successively studied with both a force platform (static condition) and a rocking platform (dynamic condition). The tests were performed 2 d before the bed-rest period, and over the 1st, 3rd and 4th days of the recovery period. When the subjects were controls, bed rest decreased step length, walking velocity, and balance stability. LBNP completely counteracted the bed-rest-induced modifications of gait and static balance and of dynamic balance for the lateral sway. As LBNP was ineffective in counteracting the modifications of the anteroposterior sway, dynamic balance deficiency was independent of the beneficial effect of LBNP on the decreased orthostatic tolerance induced by -6 degrees head-down bed rest. The results indicate that head-down bed rest, like spaceflight, induces certain sensorimotor changes involved in the decrease of gait and balance performance.

Adult↗
PubMed1992

Results of a 4-week head-down tilt with and without LBNP countermeasure: I. Volume regulating hormones.

The volume regulating hormones were studied during a 4-week head-down tilt (CNES HDT) in five subjects with and without (controls) lower body negative pressure (LBNP). LBNP was applied 3 times a day for 3 weeks, 4 times a day for 4 d, and 6 times a day for 3 d the last week. In both groups we observed a significant decrease in body weight (3% in controls, 0.8% in LBNP), a significant increase in plasma renin activity and aldosterone (with an amplification of their rhythms), and a significant decrease in norepinephrine with no difference between the two groups. The only major hormonal difference was observed for atrial natriuretic factor (ANF), which decreased significantly in the control group and increased in the LBNP group. These results are compared with the improvement in orthostatic tolerance (OT) after HDT in the LBNP group in the same protocol (17). We conclude that many factors could be involved in the improvement of OT. The results suggest that better conservation of plasma volume in the LBNP group might have prevented a decrease in ANF. Whether ANF plays a role in the regulation of baroreceptor reflex with an improvement in OT is currently unknown.

Aldosterone↗
PubMed1992

Results of a 4-week head-down tilt with and without LBNP countermeasure: II. Cardiac and peripheral hemodynamics--comparison with a 25-day spaceflight.

Cardiovascular hemodynamics were assessed by ultrasound echography and Doppler during a 28-d head-down tilt "CNES HDT: 87-88," and during the 25-d French-Soviet spaceflight "Aragatz 88." For both studies we used the same ultrasound methodology. The main hemodynamic parameters of the left heart function and of the peripheral arterial system (cerebral, renal, femoral arteries) were measured four times during the HDT (day 7, 14, 21, 28) and twice post-HDT. The same measurements were performed six times during the flight (day 4, 5, 15, 18, 20, 24) and five times postflight. During the HDT, two groups were studied: six subjects no countermeasures and six subjects with repeated lower body negative pressure (LBNP). In the first group the cardiac volumes and the cardiac output were significantly decreased, whereas in the group with LBNP these parameters were superior to the basal value. In the group without LBNP the cerebral flow was maintained because of a decrease of the brain vascular resistance. In this group the renal vascular resistance was decreased as inflight. In the lower limbs we observed a loss of the vasomotor control. The vascular resistance was decreased after the end of the HDT and the subjects suffered orthostatic intolerance. In the population with LBNP, we did not observe the same decrease of vascular resistance during the HDT, and after the HDT no sign of orthostatic intolerance was observed. During the flight, the left ventricular volume was significantly decreased. The carotid flow was maintained owing to a decrease of the cerebral vascular resistance.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Cardiovascular adaptation during simulated microgravity: lower body negative pressure to counter orthostatic hypotension.

The cardiovascular function is one of the main functions disturbed by microgravity. It is particularly affected by the astronaut's return to Earth, where one of the symptoms of the cardiovascular adaptation syndrome is orthostatic hypotension; the clinical consequence can be presyncopal state or a syncope. Lower body negative pressure (LBNP) is intended to stimulate the venous system of the lower limbs. Studies performed in the U.S. have shown that LBNP constitutes an efficient countermeasure, but this approach is impractical because 4 to 6 h/d of application are required. Five volunteers took part in two recent antiorthostatic bed rest experiments for 30 days. In the first experiment, three subjects were submitted to several sessions of LBNP per day and two others were controls; in the second, the LBNP group of the first experiment became control and vice versa. Two orthostatic investigations were performed: 5 d before bed rest; and at the end of the 30-d bed rest period. The results showed that: 1) when the subjects were controls, a high orthostatic hypotension post bed rest with three syncopes and one presyncopal state during the first minutes of the tilt test appeared; 2) when the subjects were submitted to LBNP sessions, no orthostatic hypotension was noted. These two experiments proved the beneficial effects of the LBNP as a countermeasure against orthostatic hypotension.

Adaptation, Physiological↗
PubMed1990

Haemodynamics of leg veins during a 30-days-6 degrees head-down bedrest with and without lower body negative pressure.

Venous distensibility of the lower limbs was assessed in six healthy men who were submitted twice successively to 1 month of -6 degrees head-down bedrest, with and without lower body negative pressure (LBNP) (LBNP subjects and control subjects, respectively). Venous capacity (delta Vv,max, in ml.100 ml-1) of the legs was determined by mercury strain gauge plethysmography with venous occlusion. Plethysmographic measurements were made on each subject before (Dc), during (D6 and D20) and after (5th day of recovery, D+5) bedrest. During bedrest, LBNP was applied daily, several times a day to the subjects submitted to this procedure. Results showed a gradual increase in Vv,max (ml.100 ml-1) throughout the bedrest, both in the control group [delta Vv,max = 2.11 SD 0.54 at Dc, 2.69 SD 0.29 at D6, 4.39 SD 2.08 at D20, 2.39 SD 0.69 at D+5, P less than 0.001 (ANOVA)] and in the LBNP group [delta Vv,max = 2.07 SD 0.71 at Dc, 2.85 SD 1.19 at D6, 3.75 SD 1.74 at D20, 2.43 SD 0.94 at D+5, P less than 0.001 (ANOVA)], without significant LBNP effect. These increases were of the same order as those encountered during spaceflight. It is concluded that -6 degrees head-down bedrest is a good model to simulate the haemodynamic changes induced by exposure to weightlessness and that LBNP did not seem to be a good technique to counteract the adverse effects of weightlessness on the capacitance vessels of the lower limbs. This latter conclusion raises the question of the role and magnitude of leg venous capacitance in venous return and cardiac regulation.

Adult↗
PubMed1989

[Cardiovascular deconditioning syndrome during space flight].

Weightlessness results, in Man, in a redistribution of organic fluids from the lower half of the body to the thoraco-cephalic areas. This fluid transfer is responsible, in the course of the flight, for a series of subjective and objective disorders which the astronauts will experience. These disorders are related to venous stasis in the thoraco-cephalic area. Moreover, upon return of any space mission, regardless of its length, the astronauts will experience a disadaptation of their cardiovascular system indicated by hypotension with the possible occurrence of a presyncopal state, or even a syncope and a lowered stress capability. The haemodynamic consequences of this fluid transfer, from central and peripheral standpoint, and the mechanisms implicated in the cardiovascular deconditioning syndrome, are presented and discussed.

Blood Circulation↗
PubMed1987

Reversibility of hemodynamic hypofrontality in schizophrenia.

Regional cerebral blood flow (CBF) was studied in 51 young schizophrenics. A significant decrease of CBF was seen in frontal and prefrontal regions (hypofrontal pattern) in chronic patients whose disease had evolved for more than 2 years and who were in remission. This hypofrontal pattern was reversible, as it disappeared during exacerbation of the disease. In 10 patients who had not been treated with neuroleptics for several weeks, we found a dopaminergic hypersensitivity in the frontal lobes, as a weak dose of piribedil restored near-normal frontality. This may reflect either the role of neuroleptic washout or a primitive dopaminergic depletion, as proposed by some authors in the chronic form of schizophrenia.

Adult↗
PubMed1986

Plasma vasopressin, neurophysin, renin and aldosterone during a 4-day head-down bed rest with and without exercise.

The purpose of this study was to investigate the main renal and hormonal responses to head-down bed rest, which is currently considered a reliable experimental model for the simulation of weightlessness. Urinary output and electrolytes, plasma renin activity (PRA), aldosterone (PA), antidiuretic hormone (ADH) and immunoreactive neurophysin-I (Np) were measured in eight adult volunteers submitted to a 4-day head-down bed rest (-6 degrees) after a 24-h control period in the horizontal position (day 0). Four of the eight subjects were submitted to two 1-h periods of controlled muscular exercise (50% VO2max) from day 1 to day 4. Throughout the head-down bed rest period, urinary output remained stable, although lower than in the control period (day 0), but the urinary Na/K ratio decreased. Plasma electrolytes and osmolality, and creatinine clearance remained unchanged. There was no significant difference between exercising and non-exercising subjects. At the hormonal level, PRA and PA increased during the head-down bed rest. This increase was more pronounced in the group with exercise. At the end of the tilt period, PRA and PA were about 3 times higher than on day 1. No significant changes could be observed for ADH and Np. It is concluded that a 4-day head-down bed rest results in no apparent changes in neurohypophyseal secretory activity, and in a progressive secondary hyperaldosteronism.

Adult↗
PubMed1986

Pharmacological exploration of dopamine hypersensitivity in migraine patients.

Patients with migraine show a hypersensitivity to dopamine or its agonists. One of these, piribedil, was administered as 0.1 mg/kg intravenously over 30 min to subjects with either migraine or other types of headache. This test provoked in migraine patients an increase of the cerebral blood flow and the peripheral signs of dopamine hypersensitivity:- nausea or vomiting and a rapid fall in blood pressure. In contrast, in those subjects with chronic non-migrainous headache, the administration of piribedil had no effect. The piribedil test appears to possess good specificity vis à vis migraine, enabling a differential diagnosis from atypical periodic headache, a condition difficult to consider as migraine or psychogenic headache on clinical grounds alone.

Cerebrovascular Circulation↗
PubMed1985

[Oral glucose tolerance tests in man during a 150-day space flight (Salyut 7-Soyuz T9)].

This study was conducted on the pilot specialist of the Salyut 7-Soyuz T9 complex during a 150 days space flight. Glucose tolerance tests were made 3 days before flight, on days 60 and 88 during flight and on days 25 and 55 after flight. The study confirms the decrease of fasting plasma glucose observed during the 3 Skylab missions and demonstrates blunted glucose tolerance curves. The changes were not found during ground based studies using bed rest to simulate weightlessness state. The origin of this abnormality is discussed.

Adult↗
PubMed1985

[Cerebral blood flow and meningeal hemorrhage. An aid to the surgical decision].

One hundred and eleven measurements of cerebral blood flow (C.B.F.) were performed using the Xenon 133 inhalation method in 80 cases of spontaneous subarachnoid hemorrhage of which 59 were due to ruptured aneurysms. This method is non-traumatic, reproducible and dependable. A correlation was found between clinical condition and C.B.F. values, but in a number of cases which cannot be dismissed, very low mean C.B.F. values or ischemic foci were revealed where clinical state gave no indication. A poor correlation appeared between vasospasm seen by angiography and ischemic foci detected by isotopic technique. Patients' age influenced C.B.F. values but not clinical evolution. No correlation was found between C.B.F. values and cisternal blood seen on CT scan. C.B.F. values, measured in the first two weeks of illness, were significantly higher in those patients having favorable outcome, whatever their clinical state at the time of C.B.F. measurement (comas excluded). The figure of 60 ml/100 g/min for mean cortical flow seemed to be a critical level below which the risk of complication was greater. Below this level or in cases or ischemic foci, surgery was delayed. Thus, C.B.F. measurement promises to be a valuable prognostic tool, playing an important role in the therapeutic strategy for this type of patients.

Adult↗
PubMed1985

[Circulatory and hormonal changes induced by microgravity].

The absence (or decrease) of the hydrostatic pressure during space flights (microgravity state) or simulations of weightlessness (by immersion, bed rest or head-down tilt) result in a body fluid shift and an engorgement of the central circulation where mechanoreceptors involved in plasma volume regulation are located. Their activation induces the initial (first hours) hormonal response with a decrease in plasma vasopressin, renin and aldosterone and probably an increase in a natriuretic factor (Gauer reflex). Prolonged exposure to microgravity leads to more complex and often hypothetical responses: cardiovascular deconditioning, modifications in secretion and circadian rhythms of above cited hormones. After 24 years of studies on approximately 200 astronauts our knowledge of cardiovascular and hormonal adaptation to space flight is still at the beginning.

Adaptation, Physiological↗