The effect of an L-type calcium channel blocker on the hemodynamics of orbital arteries in dogs.

Purpose: (1) To determine the effect of the l-type calcium channel blocker amlodipine on color Doppler ultrasound-determined vascular resistance and blood flow velocities in the distal retrobulbar arteries of dogs; (2) to determine any effect of blood pressure and PCO2 rate on such color Doppler-determined circulatory measurements.

Methods: Color Doppler imaging measurements of the short posterior ciliary artery, long posterior ciliary artery, and ophthalmic artery of normal eyes of 10 dogs were obtained under isofluorane anesthesia before and 1 week after oral amlodipine administration. Mean systemic arterial blood pressure and PCO2 were monitored.

Results: The mean resistive index decreased significantly in the short posterior ciliary artery (P = 0.0347), in the long posterior ciliary artery (P = 0.0092), and ophthalmic artery (P = 0.0004) following systemic amlodipine administration. The end diastolic velocity increased significantly in the long posterior ciliary artery (P = 0.0368) and ophthalmic artery (P < 0.0001). The peak systolic velocity increased significantly in the ophthalmic artery (P = 0.0256). Mean systemic arterial blood pressure was significantly negatively associated with resistive index (P < 0.0001) and significantly associated with the log of the end diastolic velocity (P < 0.0001).

Conclusions: Systemically administered amlodipine increases color Doppler imaging-determined blood flow velocity and decreases vascular resistive index in the ophthalmic artery, short posterior ciliary artery and long posterior ciliary artery of normal dogs. Changes in systemic arterial blood pressure can significantly affect the measurement of color Doppler imaging parameters.