Purpose: Prospective examination of the influence of changes in heart rate, arterial blood pressure and intraocular pressure induced by short dynamic exercise on orbital blood-flow velocities, and comparison of the autoregulation response in the ophthalmic artery and the central retinal artery.
Methods: Twelve young healthy volunteers were involved in the ophthalmic artery study and 12 others in the central retinal artery study. Blood-flow velocities were measured using color Doppler imaging before and after exercise.
Results: After exercise systolic blood pressure and heart rate were higher ( P<0.004) and intraocular pressure was lower ( P<0.006). However, in the central retinal artery the mean flow velocity, end-diastolic velocity and resistive indices remained stable, while in the ophthalmic artery these velocities actually decreased, and resistive indices increased significantly ( P<0.005). In the central retinal vein the velocities showed no significant change.
Conclusion: Our results confirm the presence of an effective compensatory autoregulation for the retinal circulation, in connection with an increase in the ocular perfusion pressure induced by exercise. However, we found that in the ophthalmic artery some over-compensation occurs (significant decrease in some velocity parameters), whereas in the central retinal artery important flow parameters (mean velocity, end-diastolic velocity and resistive indices) appear to be successfully stabilized. Exercise history, heart rate, blood pressure and intraocular pressure all have to be monitored in orbital blood flow studies, as these variables are strongly affected by the changes in the autonomic nervous system and in turn significantly influence the measured flow velocity and resistivity values.