Ophthalmic arterial hemodynamics during isometric exercise

Purpose: Isometric exercise raises systemic arterial pressure and simultaneously lowers intraocular pressure. Together, these pressor effects increase calculated ocular perfusion pressure and test the capacity for flow and pressure autoregulation in the orbital circulation. Methods: We investigated in 17 young, healthy subjects the effect of isometric exercise on ophthalmic arterial hemodynamics, as measured by color Dopp-ler imaging. Isometric handgrip was maintained for 10 min at 20% maximal force. Results: Handgrip predictably raised systolic (114 ± 2 to 122 ± 3 mm Hg; p < 0.01), diastolic (69 ± 2 to 78 ± 2 mm Hg; p < 0.01), and mean systemic pressures (84 ± 2 to 93 ± 3 mm Hg; p < 0.01). Because exercise also reduced intraocular pressure (from 14.2 ±.5 to 12.2 ±.4 mm Hg, p < 0.01), calculated ocular perfusion pressure increased from 42 ± 3 mm Hg before exericse to 50 ± 3 mm Hg during exercise (p < 0.01). Despite this pressure increase, we found no evidence for exercise-induced vasoconstriction in the ophthalmic artery: peak systolic velocity (PSV) was unaltered by exercise, whereas end-diastolic velocity (EDV) increased (from 5.8 ±.5 mm/s at rest to 8.4 ± 1.3 mm/s during exercise; p < 0.01). These velocity changes reduced the calculated resistance index ((PSV - EDV)/PSV) from 0.82 ± 0.01 at rest to 0.78 ± 0.02 during exercise (p < 0.05). Conclusion: Isometric exercise-induced increases in ocular perfusion pressure are apparently associated with reductions in vascular resistance distal to the ophthalmic artery, a result suggesting that ocular blood flow or microvas-cular pressures may be autoregulated by vascular adjustment proximal to the orbit itself.