[Changes in orbital hemodynamics caused by nitroglycerin and nifedipine. A study using color duplex ultrasound].

Color Doppler imaging has demonstrated orbital hemodynamic changes in diseases such as central vein occlusion, the ocular ischemic syndrome and diabetic retinopathy. Reports of pharmacologically induced changes are, however, rare and inconsistent. In order to verify the sensitivity of color Doppler imaging to demonstrate pharmacologically induced changes in orbital hemodynamics, nitroglycerin and nifedipine served as vasoactive agents with a clear pharmacological spectrum. Twelve healthy volunteers were examined before and after drug application. After the administration of 0.8 mg nitroglycerin, the end diastolic bloodflow velocity was increased in the central retinal artery (before: Vdiastolic 2.2 +/- 1.0 cm/s, after: Vdiastolic 3.1 +/- 1.1 cm/s) as well as the ophthalmic artery (before: Vdiastolic 5.8 +/- 1.7 cm/s, after: Vdiastolic 7.4 +/- 1.8 cm/s). The resistance index of orbital blood flow decreased in all three vessels. After sublingual administration of 10 mg nifedipine, peak systolic blood flow velocity was slightly higher in the ciliary arteries and in the ophthalmic artery (before: Vsystolic 34.7 +/- 4.6 cm/s, after: Vsystolic 37.8 +/- 3.6 cm/s). Blood-flow velocity in the central retinal vein was elevated as well (before: Vmax 3.81 +/- 0.66 cm/s, after: Vmax 4.66 +/- 0.83 cm/s). Those slightly divergent results may be due to the different pharmacological spectrum of the two drugs investigated While nitroglycerin leads to dilatation of venous vessels, nifedipine acts primarily on small arteries. As nifedipine and other calcium channel blockers have been tested in patients with low-tension glaucoma, future color Doppler studies of such a population seem to be promising.