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Biomedical subjects

A Bes

Publications and source records attributed to A Bes.

At least 19 recordsLinked to original sources
PubMed1997

Cardiovascular and hormonal changes induced by a simulation of a lunar mission.

BACKGROUND: This is the first simulation of a 14-d lunar mission including 6 d on the Moon. HYPOTHESIS: We hypothesized that a lunar gravity simulation in the middle of a head-down tilt (HDT) might result in some reversal of body fluid/hormonal responses, and influence cardiovascular deconditioning. METHODS: Six men (28 +/- 2.5 yr) were placed in bed rest (BR): in (HDT) (-6 degrees) to simulate microgravity during the travel (two 4-d periods), and in head-up tilt (HUT) (+10 degrees) (6-d period) to simulate lunar gravity (1/6 g). Muscular exercise was performed during the HUT period to simulate 6 h of lunar EVA. Heart rate variability (HRV) and hormonal responses were studied. RESULTS: An orthostatic arterial hypotension was observed after the BR (tilt test) in 4 of the 6 subjects. Plasma volume measured at D14 decreased by -11.1% (vs. D-3, sitting position). A decrease in atrial natriuretic peptide (26 +/- 3.5 pg.ml-1 (D14) vs. 37.9 +/- 3.5 pg.ml-1 (D-3, sitting) and an increase in plasma renin activity (198 +/- 9.2 mg.L-1.min-1 (D14) vs. 71 +/- 9.2 mg.L-1.min-1 (D-3, sitting) were observed during the BR, more pronounced in HUT at 7:00 p.m. Sympathetic-parasympathetic balance (HRV) at rest showed a decrease in parasympathetic indicator and an increase in sympathetic indicator in BR (p < 0.05), without differences within HDT and HUT periods. CONCLUSION: These changes were mostly similar to those reported in spaceflights, and HDT. Although the exposure to 1/6 g with exercise modified some hormonal and body fluid responses, this partial gravity simulation was not sufficient to prevent the decrease in orthostatic tolerance observed here as well as after Apollo lunar missions.

Adult↗
PubMed1995

Effects of 28-day head-down tilt with and without countermeasures on lower body negative pressure responses.

This study was performed to determine the effects of 28 d of head-down tilt (HDT) (simulated weightlessness) on cardiovascular responses to orthostatic stress induced by lower body negative pressure (LBNP) (before, during, and after HDT) and +60 degrees head-up tilt (before and after HDT) in 12 subjects. Half of them underwent countermeasures (CM) of regular muscular exercise (isometric and isokinetic training) and LBNP sessions (-30 mm Hg) as generally performed during spaceflight; the other six were a control group (C). The countermeasure effect on the orthostatic responses to LBNP and tilt test was assessed by studying the changes after HDT in the two groups. Essentially, blood pressure was better maintained in group CM in the tilt test after HDT (MBP at the end of the tilt vs. baseline value: +16% (CM); -19% (C)). LBNP and muscular exercise may have contributed to this improvement. One of the probable contributing factors is the relative conservation of plasma volume, at the end of HDT, in group CM (-2.2%), compared to group C (-11.2%). Transcranial Doppler (TCD) recordings of middle cerebral artery (MCA) velocities permitted indirect evaluation of cerebral blood flow changes during the orthostatic tests. MCA velocities decreased significantly although slightly (-7 to -12%) during LBNP sessions without changes along the HDT showing that the cerebral circulation was well preserved in each group. On the other hand, subjects undergoing presyncopal symptoms presented a drop in MCA velocities, suggesting a decrease in cerebral blood flow.

Adult↗
PubMed1994

[Orthostatic hypotension after space flight].

Cardiovascular changes occur during spaceflight. Because of the loss of hydrostatic pressure there is, during weightlessness, a fluid shift of extra- and intra-vascular volumes to the upper part of the body. This provokes objective and subjective symptoms, especially in the first days of spaceflight. The fluid shift is perceived by baroreceptors as a relative central hypervolaemia and induces neuro-hormonal mechanisms which provoke a real hypovolaemia. Cardiovascular deconditioning exists during spaceflight with the following symptoms when astronauts return to earth: decreased orthostatic tolerance with possible tendency towards spontaneous syncope and decreased effort capacity. The mechanisms of orthostatic intolerance are not well known. Several factors are probably involved, including hypovolaemia, modifications of the venous system, baroreflex changes, etc. Various countermeasures have been tested in microgravity simulations on the ground, then in flight.

Cardiovascular Deconditioning↗
PubMed1994

Psychomotor performance during a 28 day head-down tilt with and without lower body negative pressure.

Several factors may affect psychomotor performance in space: sensory-motor changes, sleep disturbances, psychological modifications induced by the social isolation and confinement. However, psychomotor performance is difficult to assess. A battery of standardized and computerized tests, so-called "Automated Portable Test System" (APTS) was devised to ascertain the cognitive, perceptive and motor abilities and their possible fluctuations according to environmental effects. Antiorthostatic bedrest, often used to simulate weightlessness, (particularly cardiovascular modifications) also constitutes a situation of social confinement and isolation. During two bedrest experiments (with head-down tilt of -6 degrees) of 28 days each, we intended to assess psychomotor performance of 6 males so as to determine whether: on the one hand, it could be altered by remaining in decubitus; on the other, the Lower Body Negative Pressure sessions, designed to prevent orthostatic intolerance back on Earth, could improve the performance. To accomplish this, part of the APTS tests as well as an automated perceptive attention test were performed. No downgrading of psychomotor performance was observed. On the contrary, the tasks were more accurately performed over time. In order to assess the experimental conditions on the acquisition phase, the learning curves were modelled. A beneficial effect of the LBNP sessions on simple tests involving the visual-motor coordination and attention faculties can only be regarded as a mere trend. Methods used in this experiment are also discussed.

Adult↗
PubMed1993

[Creutzfeldt-Jakob disease after treatment with human extracted growth hormone. A clinicopathological study].

This report describes the pathological changes observed in the brain of a 18-year-old patient who died with Creutzfeldt-Jakob disease (CJD) of the ataxic and panencephalopathic type. Clinically, the disease began at age 17 with a rapidly progressive cerebellar syndrome, associated with myoclonus and mental deterioration. Cranial CT scan and MRI showed minor abnormalities. EEG demonstrated non specific changes. The patient became progressively demented, bedridden and died 10 months after the onset. Nine years earlier, he had been operated upon for craniopharyngioma and subsequently treated with cadaver-derived human growth hormone. Post-mortem examination of the brain revealed mild diffuse atrophy. Histology showed congophilic amyloid plaques found in both gray and white matters of the cerebrum and cerebellum, associated with spongiosis, mainly in the basal ganglia and cerebellum, and gliosis. They were immunostained with antiprion protein antibody using the immunoperoxidase method on paraffin embedded sections. The clinical findings in this case were similar to those of other cases of human growth hormone-associated CJD. However, this case is unusual because of the great number of amyloid plaques, which have been only rarely found in previous reports.

Amyloid↗
PubMed1992

[Cerebral blood flow in migraine without aura].

For several years, cerebral blood flow (CBF) studies have been fueling the controversy surrounding the pathophysiology of migraine headache. The earliest studies focused mainly on migraine with aura (MA+) and provided evidence in support of the classical hemodynamic theory: a decrease in blood flow during the aura is followed by reactive vasodilation during the headache phase. Studies in migraine without aura (MA-), although less numerous, consistently demonstrated an increase in CBF during the attack. Olesen et al., gave rise to a heated debate by suggesting that hemodynamic manifestations are different in MA+ and MA-; in their view, CBF remains unchanged in MA-, whereas MA+ is associated with a wave of posterior blood flow deficiency which slowly spreads forwards in a manner reminiscent of experimental spreading depression; they interpret this hemodynamic pattern as evidence that the attack is mainly caused by a neural mechanism rather than a vascular spasm. This concept of MA- with no hemodynamic changes suggests that the pathophysiology of MA- may be completely different from that of MA+. However, most studies using stationary detectors or single photon emission computerized tomography (SPECT) with Xenon 133 or HMPAO as the tracer have demonstrated increased CBF during migraine attacks. The increase was not correlated with the side of the pain suggesting that vasodilatation is not the only cause of the pain. Current data do not seem to support the view that MA- and MA+ are different pathophysiologic entities; whether the mechanism of the attack is neural or vascular cannot be determined on the basis of CBF data.(ABSTRACT TRUNCATED AT 250 WORDS)

Cerebrovascular Circulation↗
PubMed1988

A multi-centre, double-blind trial of tizanidine, a new antispastic agent, in spasticity associated with hemiplegia.

A double-blind study was carried out in 105 patients with chronic spasticity associated with hemiplegia in order to compare the efficacy and tolerability of tizanidine with that of diazepam. Dosage was increased progressively, if tolerated, to a maximum of 24 mg tizanidine or 30 mg diazepam per day at the end of 2 weeks. The optimum dosage was then maintained for 6 weeks. Efficacy and tolerability parameters were assessed after 2 and 8-weeks' therapy. Patients on tizanidine but not those on diazepam showed a statistically significant improvement in functional status, as assessed by walking distance on flat ground. Analysis of the stretch reflex in four groups of muscles showed that both tizanidine and diazepam reduced the duration of contractions and increased the angle at which contraction occurred, but there were no significant differences between the two drugs. Clonus of the triceps surae resolved in 48% of tizanidine and 40% of diazepam patients. Evaluation of the effect of therapy revealed an improvement with each drug in approximately 83% of patients, with the overall evaluation being slightly (but non-significantly) in favour of tizanidine. There were fewer discontinuations of treatment in the tizanidine group as a result of side-effects. It would appear, therefore, that tizanidine is an effective and well-tolerated drug in the treatment of cerebral spasticity.

Adolescent↗
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↗
PubMed1987

[A case of centronuclear myopathy in adults with facio-scapulo-peroneal topography].

A 34 year-old man had complained since childhood of weakness of the right lower limb. His mother had a myopathy. Examination showed weakness and amyotrophy of the antero-external regions of the legs, mainly on the left, moderate weakness of the right scapular girdle and slight facial weakness. Serum creatine kinase was increased. Electromyogram and CT scan images were of the myogenic type. Biopsy showed a centronuclear myopathy. The course was slowly progressive. Centronuclear myopathy is rare in adults. The facio-scapulo-humeral localization has been described in numerous other pathologic types of myopathy.

Adult↗
PubMed1986

[Acebutolol and cerebral blood flow of the moderately hypertensive aged subject].

In 17 moderate hypertensive patients (mean age = 67 +/- 8.8) the effects of a chronic oral administration of the beta blocking agent acebutolol on regional cerebral blood flow (rCBF) was studied using the non invasive 133 Xenon inhalation technique. The results was compared to the rCBF obtained in an age matched normal control group. Our study shows that during long term therapy low doses of acebutolol (200 mg/daily) the rCBF is unaffected by a decrease (20 mmHg) of the mean arterial blood pressure. The relative hypofrontality of the elderly hypertensive patients leads to be corrected by acebutolol.

Acebutolol↗
PubMed1986

[Migraine and the idiopathic Raynaud phenomenon].

The successive onset of spasms of distal arteries of the limbs and complicated migraine in a young migrainous woman raised the possibility of a common mechanism for both disorders. Three similar cases have been reported and two recent epidemiological studies have shown the frequent association of migraine attacks and Raynaud's phenomenon or variant angina in a individual patient. The possible role of vasospasm in triggering the migrainous aura is discussed.

Adult↗