Blood flow in the human optic nerve head (ONH) during isometric exercises

Purpose Autoregulation of optic nerve head blood flow (F-onh) in response to decreases in perfusion pressure has been demonstrated in animals and humans. The aim of this study was to determine change in F-onh when systemic blood pressure is increased. Methods Blood flow parameters, i.e. relative mean velocity, number, and flux of red blood cells in the ONH tissue (Vel(onh), Vol(onh) and F-onh, respectively) were measured by laser Doppler flowmetry in one eye of 13 normal subjects (aged 16 to 58 years), at baseline, during, and after isometric exercises consisting of squatting. Brachial artery blood pressure was measured by sphygmomanometry. IOP was mesured at baseline and at the end of squatting. Results During squatting mean arterial presure increased from 103 +/- 6 mm Hg to 139 +/- 58 mm Hg (average +/- 95% confidence interval), IOP increased from 13 +/- 0.5 to 17 +/- 1 mm Hg. An average increase in PP, from 56 +/- 4 to 80 +/- 7 mm Hg induced no significant (p > 0.05) change in the blood flow parameters. The sensitivity (detection threshold) of the blood flow changes was 8%. Conclusion This study shows for the first time in human autoregulation of F-onh when PPm is increased by increasing the systemic blood pressure.