[Laser Doppler flowmetry of the bulbar conjunctiva as a monitor of the cerebral blood flow].

In order to develop a non-invasive monitor of cerebral blood flow during aortic arch surgery, reliability of the laser Doppler flowmetry of the bulbar conjunctiva was evaluated. The blood flow of the bulbar conjunctiva may represent the cerebral blood flow because the ophthalmic artery originating from the internal carotid artery supplies the blood to the bulbar conjunctiva. A laser Doppler flowmeter (Advance Co., ALF201) and a specially designed probe was prepared to measure the blood flow of the bulbar conjunctiva. The probe was designed to stay in a fixed position on the bulbar conjunctiva when the eye lid is closed, so that it can maintain a stable measurement. The shape of probe is a small box, 7.5 x 4.0 x 2.0 mm connected to a glass fiber cable 2 mm in diameter, as the signal to convey to the flowmeter. Eight mongrel dogs were used for the experimental study. The brachiocephalic vessels were exposed to measure the pressure and the blood flow of the carotid arteries. The blood flow of the cerebral cortex and the bulbar conjunctiva was measured by the laser Doppler flowmetry. When the carotid artery was clamped, the blood flow of the bulbar conjunctiva fell instantaneously in 1.35 +/- 0.85 seconds and reached the plateau in 9.60 +/- 4.15 seconds. The flow returned to the previous value in 7.70 +/- 3.75 seconds after the clamp was removed. A significant positive correlation between the blood flow of the bulbar conjunctiva and that of the cerebral cortex was observed (r = 0.78, p < 0.001, n = 2). When the extracorporeal circulation was used, the waveform of the bulbar conjunctival blood flow was synchronized to the small pulse wave generated by the pump. Although the measurement of the bulbar conjunctival blood flow by laser Doppler flowmetry is an indirect method of monitoring the cerebral blood flow, it can provide non-invasive, continuous, and reliable measurement. We conclude that this is a useful method to monitor the cerebral blood flow during aortic arch surgery.