CHOROIDAL BLOOD-FLOW DURING ISOMETRIC EXERCISES

Purpose. To investigate the response of choroidal blood flow in the fo veal region of the human eye to increases in mean perfusion pressure ( PPm = mean ophthalmic artery pressure - intraocular pressure IOP) indu ced by isometric exercises. Methods. Using laser-Doppler flowmetry, ch anges in velocity (ChBVel). number (ChBVol), and flux (ChBF) of red bl ood cells in the choroidal vascular system in the foveal region of the fundus were measured in bath eyes of 11 normal subjects (ages 18 to 5 7 years) during isometric exercises. Results. During 90 seconds of squ atting, PPm increased by an a average of 67%, from 46 to 77 mm Hg. Thi s resulted in a significant increase of 12% in ChBF(m) (the mean of Ch BF during the heart cycle), mainly caused by an increase in ChDVel(m). A further increase in PPm to a value approximately 85% above baseline resulted in a 40% increase in ChBF(m). A significant negative correla tion was found between the changes in ChBVel(m) and ChBVol(m) during s quatting. Conclusions. Previous studies have demonstrated that during isometric exercise, blood pressures in the ophthalmic and brachial art eries rise in parallel. These observations and the current results ind icate that an increase in PPm up to 67% induces an increase in choroid al vascular resistance that limits the increase in choroidal blood flo w to approximately 12%. This regulatory process fails when PPm is furt her increased.