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Biomedical subjects

A Guell

Publications and source records attributed to A Guell.

At least 37 records · Page 2Linked to original sources
PubMed1990

Cardiovascular deconditioning during weightlessness simulation and the use of lower body negative pressure as a countermeasure to orthostatic intolerance.

The cardiovascular function is one of the main disturbed by weightlessness: it is particularly affected by the astronaut's return to Earth, where symptoms linked to the cardiovascular deconditioning syndrom appear in the following forms: (1) orthostatic intolerance with its risk of syncope: (2) higher submaximal oxygen consumption for an equivalent work load. Lower Body Negative Pressure (LBNP) is intended to stimulate the venous system of the lower limbs; however, the specific effects of periodical LBNP sessions on the orthostatic intolerance have never been studied. With this objective in mind, 5 volunteers took part in two recent antiorthostatic bedrest experiments for 30 days. In the first experiment 3 subjects were submitted to several sessions of LBNP experiment per day and 2 others were controls; in the second experiment the LBNP group of the 1st one became controls and vice-versa. Two orthostatic investigations were performed: (1) 5 days before the bedrest; (2) at the end of the 30 day bedrest period. The results showed: (1) when the subjects were control, a high orthostatic intolerance post bedrest with 3 syncopes and one presyncopal state during the first minutes of the tilt test; (2) when the subjects were submitted to LBNP sessions, no orthostatic intolerance.

Adult↗
PubMed1990

Voice analysis to predict the psychological or physical state of a speaker.

A vocal message, apart from its semantic content, carries information on the psychological and physiological condition of the speaker. Physical fatigue and especially psychological stress are the pathological elements of the condition. The accepted term for the cause of these effects is the "workload." This article describes the main research carried out since the 1940's to measure the acoustic modifications of the voice brought about by a workload. It concludes by a critical analysis of the studies and a short description of the perspectives for research. Their results mainly concern astronauts and pilots involved in specific high-stress tasks and possible users of voice recognition systems. All the studies show an excellent approach to this field of research but deserve to be widened, deepened, and made more accurate to enable estimating the nature or level of reaction to a workload.

Aerospace Medicine↗
PubMed1989

Propranolol does not alter cerebral blood flow and functions in cirrhotic patients without previous hepatic encephalopathy.

Since it has been suggested that propranolol could lead to hepatic encephalopathy, we undertook a study to assess the effects of propranolol on cerebral blood flow and cerebral functions. Sixteen patients with alcoholic cirrhosis and large esophageal varices and without major hepatic dysfunction (Child-Pugh score less than 14) or previous hepatic encephalopathy were randomized to receive either propranolol or placebo. The following measurements were performed before and 15 min after single intravenous administration of 15 mg propranolol or placebo and again 1 week after chronic oral administration of propranolol 160 mg per day or placebo: cerebral blood flow by the xenon-133 inhalation technique, quantitative electroencephalogram, psychometric test (number connection test), arterial ammonia, pH and pCO2, resting and exercise heart rates (after single administration, electroencephalogram, number connection test and biochemical measurements were not performed). Cerebral blood flow was not significantly modified by treatment (propranolol group: 80 +/- 23 vs. 76 +/- 11 and 83 +/- 9; placebo group: 73 +/- 10 vs. 75 +/- 11 and 81 +/- 18 ml per 100 gm per min, respectively, before and after single and repeated administration). Likewise, neither of the two treatments significantly altered number connection test, quantitative electroencephalogram index, arterial ammonia, pH and pCO2. We conclude that, in this population of cirrhotic patients, propranolol did not alter cerebral blood flow or neuropsychological functions. As a consequence, hemodynamic alterations cannot be considered as causes of possible cerebral side effects of propranolol in cirrhotic patients without severe hepatic dysfunction and previous hepatic encephalopathy.

Ammonia↗
PubMed1989

Astronaut behavior in an orbital flight situation: preliminary ethological observations.

Following the ethological approach, astronaut behavior is divided into "observable" motor acts which make possible its quantitative description. Frame-by-frame analysis of current videotape recordings shows that the behavioral adaptation to weightlessness is achieved through various processes. Among these are new motor acts and stereotyped movements (successive movements of head, eye, arm, and hand), reversal and reorganization of the sequence of the motor acts to form new patterns (head and eye movements upward or downward), construction of a particular cognitive image of the astronaut's own world (more compensatory regulations than anticipatory processes), and the relationship between postures and orientations according to the proximate visual environment. Furthermore, the present analysis confirms physiological data showing a redistribution of activity between flexor and extensor muscles, and a differential adaptation of vestibulo-ocular reflexes. Thus, this approach suggests new physiological experiments and enables the prediction of behavioral changes occurring during adaptation in microgravity.

Humans↗
PubMed1988

Early hormonal effects of head-down tilt (-10 degrees) in humans.

The aim of this study was to determine the effects of a 5-h weightlessness simulation (using supine bed rest or head-down tilt at -10 degrees = HDT) on plasma renin activity (PRA), aldosterone (PA), and catecholamines (epinephrine-E, norepinephrine-NE, and dopamine-DA) and to compare the results with those obtained with horizontal bed rest (BR), which is often taken as a control situation for simulation studies. Ten healthy young volunteers submitted to the three following postural tests: 7 h sitting; 1 h sitting, 5 h supine, and 1 h sitting; 1 h sitting, 5 h HDT, and 1 h sitting. Our results show that a 5-h HDT or BR induced a significant progressive increase in plasma volume (14.5% for HDT and 7% for BR) and a decrease in diastolic blood pressure (18% for HDT and 17% for BR), PRA (60% for HDT and 40% for BR), PA (63% for HDT and 60% for BR), and NE (20% for HDT and 25% for BR) compared to the sitting position. E decreased only in HDT, and DA was unchanged. We concluded that the main part of the cephalad shift is achieved by bed rest as reflected by changes in hematocrit and plasma protein concentration. The decrease in diastolic blood pressure, the inhibition of the renin-angiotensin aldosterone system (in part explained by a decrease in NE) are similar in BR and HDT. We demonstrate that the use of a relevant body position as control is a major concern when investigating the hormonal effects of HDT. If recumbency is chosen as the control situation in HDT studies, it is not surprising to observe only few changes when HDT is applied.

Adrenal Medulla↗
PubMed1986

Cardiovascular system and microgravity simulation and inflight results.

Main results of cardiovascular investigation, performed with ultrasound methods during the common French/Soviet flight aboard Salyut VII in June 1982, are compared to variations of the same parameters studied during ground-based simulations on the same subject or observed by other investigators during various ground-based experiences. The antiorthostatic bed rest simulation partly reproduces microgravity conditions and seems to be better adaptated to cardiac hemodynamics, despite some differences, and to the cerebral circulation, than to the inferior limb circulation.

Aerospace Medicine↗
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↗
PubMed1985

Epinephrine, norepinephrine, and dopamine during a 4-day head-down bed rest.

Head-down bed rest at an angle of 6 degrees was used as an experimental model to simulate the hemodynamic effects of microgravity, i.e., the shift of fluids from the lower to the upper part of the body. The sympathoadrenal activity during acute (from 0.5 to 10 h) and prolonged (4 days) head-down bed rest was assessed in eight healthy men (24 +/- 1 yr) by measuring epinephrine (E), norepinephrine (NE), dopamine (DA), and methoxylated metabolite levels in their plasma and urine. Catecholamine (CA) and methoxyamine levels were essentially unaltered at any time of bed rest. Maximal changes in plasma were on the second day (D2): NE, 547 +/- 84 vs. 384 +/- 55 pg/ml; DA, 192 +/- 32 vs. 141 +/- 16 pg/ml; NS. After 24 h of bed rest, heart rate decreased from 71 +/- 1 to 63 +/- 3/min (P less than 0.01). Daily dynamic leg exercise [50% maximum O2 uptake (VO2 max)] used as a countermeasure did not alter the pattern of plasma CA during bed rest but resulted in a higher urinary NE excretion during postexercise recovery (+45% on D2; P less than 0.05). The data indicate no evident relationship between sympathoadrenal function and stimulation of cardiopulmonary receptors or neuroendocrine changes induced by central hypervolemia during head-down bed rest.

Adult↗
PubMed1985

[Effects of cranioplasty on neurological function and cerebral blood flow].

The authors present a review of their experience of cranioplasty in cases showing of skull defects. Forty recent case reports were retained out of a total of 125 cases and of these, 15 showed neurological deficiency prior to cranioplasty. In 7 out of these 15 cases cranioplasty appeared to have no effect, but in the 8 remaining cases, an improvement in the neurological condition was observed. In connection with these clinical observations, a recent study of a small group of patients with skull defects used the Xenon 133 inhalation method to investigate cerebral blood flow. In all cases these was a significant postoperative improvement in cerebral blood flow. The rate varying from 15 to 30% and this improvement was even observable in the case of small skull defects of the order of 10 cm2. The mechanism giving rise to such improvements is discussed; it may be related to cerebral hemodynamic normalization after skull restoration. The improvement in cerebral blood flow brought about by cranioplasty in all the cases studied suggests that this technique may be important not only for simple skull repair but also to improve neurological function.

Cerebrovascular Circulation↗