PubMed Health⌕ Search

Biomedical subjects

P Quandieu

Publications and source records attributed to P Quandieu.

At least 19 recordsLinked to original sources
PubMed1999

Evaluation of cerebral stresses under acceleration taking into account the lateral ventricles.

In certain flight configurations, fighter pilots are exposed to high Gz acceleration that may induce inflight loss of consciousness (LOC). That LOC is usually preceded by visual prodromes as greyout and blackout. The pathophysiological cause of these phenomena is used to be related to the effects of accelerations on the vascular system (Burton, 1988; Whinnery, 1990). However technological advances have created aircraft generating high accelerations with rapid onset rates (1-6 Gs-1). The symptomatology of inflight LOC has changed and prodromes no longer appear. Pilots also reported a lacunar amnesia of the LOC. In order to evaluate the potentially adverse effect of acceleration on the brain tissue, it was important to study its mechanical behavior under hypergravity. An approximation of the cerebral stresses was obtained by coupling an 'ex vivo' experiment (Guillaume et al., 1997) with a numerical simulation. Firstly, the calculations have been realized considering the brain as homogeneous. Secondly, the cerebral ventricles have been individualized. The results of these two approaches were compared.

Acceleration↗
PubMed1997

Effects of perfusion on the mechanical behavior of the brain-exposed to hypergravity.

In certain flight configurations, fighter pilots are exposed to high Gz acceleration which may induce inflight loss of consciousness (G-LOC). In order to study the mechanical effects induced by these accelerations on the cerebral structures, an experimental model has been developed in vitro. Fresh bovine brains were excised and placed in a transparent mold modeling the inside of the skull. Half of these brains were perfused during the experiment. This assembly was placed into the gondola of a centrifuge, in front of a camera lens. Displacements and deformations of the brains were filmed and recorded at different onset rates. Measurements were made after off-line digitalization of images. Experimental data were incorporated into a finite element calculation code whose mesh represented the brain. The applied behavior law was elastic, the structure being considered as homogeneous and isotropic. The first results concerned the elastic properties of the brains under hypergravity. The mean value of the Young's modulus of the nonperfused brain was 46.8 kPa, which corresponded to the values published in reference literature. For the perfused brains, the mean value of the Young's modulus was higher. The mean value of the equivalent Poisson's ratio was 0.35. In fact, contrary to impacts, the mechanical stimulation is long enough to allow fluid displacements. The mean value of the equivalent Poisson's ratio calculated in the present study should probably be increased since this study was performed post mortem.

Aerospace Medicine↗
PubMed1996

Bioenergetic effects of repeated +Gz acceleration on rat heart: a 31P-NMR study on isolated hearts.

This investigation was designed to determine whether repeated exposure to high sustained +Gz acceleration induces persisting changes in the myocardial energetic metabolism. Rats were exposed to three plateaus of 30 s at 10 +Gz, four times a week, for 4 weeks. Myocardial concentrations of high-energy phosphorylated compounds were evaluated by 31P-nuclear magnetic resonance (NMR) spectroscopy on isolated hearts submitted to isovolumic aortic perfusion. Heart performances were recorded using the intraventricular balloon method. Compared to the hearts of control rats (n = 5), the hearts of centrifuged rats (n = 5) had higher concentrations of inorganic phosphate (Pi:1.40 +/- 0.33 nM vs. 0.36 +/- 0.07 mM; p < 0.01), decreased phosphocreatine concentrations (PC:15 +/- 0.39 mM vs. 15.69 +/- 0.19 mM; p < 0.01), and a lower left ventricular developed pressure (LVDP) (21 +/- 1 mmHg vs. 34 +/- 2 mmHg; p < 0.01). The workload was increased by sequential augmentation of calcium in the perfusion medium. The relationship between LVDP and the Pi/PC ratio showed that the cost of the cardiac work was greater for the centrifuged rats.

Animals↗
PubMed1993

Modeling and numerical simulation of the cerebral blood flow under acceleration.

When fighter aircrafts change directions, the pilots are subject to a centrifuge force. This force can be enough to induce the pilot loss of consciousness (LOC). The physiological cause of this LOC is a brain hypoxia which results from the increase of the hydrostatic pressure. Under gradual onset rate + Gz acceleration (GOR+Gz), the brain hypoxia occurs with visual prodromes familiar to fighter pilots. In this case, they feel a reduction of the peripheral vision (Grey-out), followed by a loss of the central vision (Black-out). The useful time of consciousness can be prolonged by using anti-G suit. Under rapid onset rate +Gz acceleration, a new symptomatology of the LOC, characterized by the absence of a grey or black-out, has been observed. The objective of this theoretical study is a better understanding of mechanisms which cause fighter pilot inflight LOC. A physical model has been developed. It allows to take into account the influence of the rate of change in acceleration on the cerebrovascular system behavior.

Acceleration↗