A comparison between laser interferometric measurement of fundus pulsationand pneumotonometric measurement of pulsatile ocular blood flow 2. Effectsof changes in pCO(2) and pO(2) and of isoproterenol

Purpose We have shown in the companion paper that, under baseline condition s, there is a high degree of association between laser interferometrically measured fundus pulsation amplitude (FPA) and pneumotonometrically measured pulse amplitude (PA) and pulsatile ocular blood flow (POBF). The present s tudy investigated the effect of high pCO(2) of high pO(2) and of isoprotere nol on POBF as assessed with laser interferometry and pneumotonometry. Methods Pneumotonometry; and laser interferometry were performed in young h ealthy subjects during breathing of 100% O-2 (n = 10; hyperoxia) and of 5% CO2 + 95% air (II = 8; hypercapnia). In addition these parameters were stud ied during stepwise increasing doses of isoproterenol, a beta-receptor agon ist (Ir = 8). Results Inhalation of 5% CO2 + 95% air increased FPA (24 +/- 12%, p < 0.001 ), PA (26 +/- 13%, p < 0.001) and POBF (15 +/- 8%, p = 0.002). Inhalation o f 100% O-2 decreased FPA (-5 +/- 7%, p = 0.027), but did not change PA or P OBF. The effect of 100% O-2 inhalation on FPA in the optic disc was more pr onounced (-11% to -20%) than in the macula. Isoproterenol caused a dose-dep endent increase in FPA, PA and POBF (p < 0.001). The association between th e induced changes in FPA and PA or POBF was highly significant Conclusions The present study shows that FPA can be taken as a valid relati ve measure of pulsatile choroidal blood flow. Our results in the optic disc indicate that FPA at the neuroretinal rim and at the cup is influenced by retinal and choroidal circulation.