The effect of hypoxia on intra-ocular, mean arterial, retinal venous and ocular perfusion pressures.

INTRODUCTION: High altitude hypoxia is linked to decreased blood oxygen saturation with a related increase of Endothelin-1 (ET-1) blood plasma levels. As a consequence of such elevated ET-1 levels, alterations of retinal venous and ocular perfusion pressures are suspected. PURPOSE: To measure the effect of hypoxia on intra-ocular pressure, mean arterial pressure, retinal venous pressure and to calculate ocular perfusion pressure. METHOD: An experimental, prospective cohort study with 33 healthy subjects was conducted in which the subjects were confronted with long-term (days) environmental hypoxia at high altitudes. Mean arterial pressure, arterial blood oxygen saturation, intra-ocular pressure, retinal venous and ocular perfusion pressure were measured at 300 m/1'000 ft (baseline), 4200 m/13'800 ft and 6000 m/19'700 ft above sea level. RESULTS: Arterial oxygen saturation (-13.06% ± 4.69, p = < 0.001; -23.46% ± 5.7,p = < 0.001), retinal venous pressure (+7.16 m Hg±8.2, p = < 0.001;+9.9 mm Hg±8.5, p = < 0.001) and ocular perfusion pressure (-8.49 mm Hg±10.6, p = < 0.001; -6.02 mm hg±11.2, p = 0.006) changed significantly from baseline at both high altitude of 4200 and 6000 m. Intra-ocular pressure did not change significantly at all altitudes (+1.16 mm Hg±4.5, p = 0.227; +0.84 mm Hg±4.8, p = 0.286) and mean arterial pressure changed significantly only at an altitude of 6000 m (+3,8 mm Hg±21.1, p = 0.005) from baseline. CONCLUSION: As hypoxia increases with higher altitude, arterial oxygen saturation and ocular perfusion pressure decreased, retinal venous pressure increased, intra-ocular pressure remains stable and mean arterial pressure was elevated only at 6000 m.

[Neurological diseases and suicide: from neurobiology to hopelessness]. / Maladies neurologiques et suicide: de la neurobiologie au manque d'espoir.

Neurologic diseases expose at a high risk of suicidal behaviors and they constitute a privileged domain for exploring the heterogeneity of underlying mechanisms. They are in fact characterized by strictly biological injuries that may be involved in cerebral systems considered at the basis of neurobiological vulnerability for suicide. At the same time, they oblige a numberof existential topics to emerge, as the hopelessness in respect of several particularly severe conditions without an etiologic treatment. A clinical approach reserving an unconditional listening can prevent a suicidal attempt. Furthermore, it can illustrate the role of the liaison's psychiatrist, who tries to transform a hopelessness situation into a patient's personal questioning and try to be present when therapeutic action is not longer possible.