Évaluation de la régulation de l'oxygénation dans les capillaires de la tête du nerf optique suivant un effort physique dynamique
It is generally accepted that ocular vascular beds have the ability to autoregulate their blood flow to counter balance the variations in the ocular perfusion pressure (OPP). Many studies have tried to evaluate this mechanism by quantifying the effects of a variation in OPP on the ocular blood flow (OBF). This was induced by either exercise or scleral suction which increases intra-ocular pressure (IOP). However, the methods used for these measurements have many disadvantages and limitations, which deters their clinical use. Recent developments in the field of non-invasive investigation of ocular blood parameters propose a model for the measurement, in real-time, of oxygen concentration in the blood streams, another important parameter of the retinal metabolism. In the present study, this new model is used to evaluate the effects of dynamic physical efforts on the blood oxygenation in the optic nerve head capillary structures (BOONH) in young healthy subjects. Six non-smoking young men participated in the study. 15-minute sessions of stationary bicycle leading to a heart rate of 160bpm were performed as dynamic physical effort. The BOONH was measured before and immediately after the exercise. The blood pressure (BP) and the IOP were measured periodically while the heart rate and the oxygen saturation in blood (SpO2) were measured in a finger throughout the exercise. The physical effort led to a reduction of the IOP in all subjects, a decrease in the BOONH in all but one subjects and a constant SpO2 in all subjects. A quadratic correlation was observed between the variations in IOP and in BOONH. These results suggest a direct correlation between the variations in BOONH and those of the OPP and the BP. The results of the present study suggest that the variations in BOONH in a healthy subject following a physical dynamic effort could indicate his/her capacity to compensate for such an effort. Moreover, the metabolic changes in the blood due to physical dynamic efforts could be a common cause of the variations in IOP and BOONH.
Oxymetry Spectrophotometry Exercise Ocular blood flow Oxygen concentration Autoregulation Intraocular pressure Optic nerve Blood pressure Retinal metabolism