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Ophthalmic artery blood flow velocity increases during hypocapnia

2004; Springer Science+Business Media; Volume: 51; Issue: 4 Linguagem: Inglês

10.1007/bf03018245

1496-8975

Lorri A. Lee, Monica S. Vavilala, Arthur M. Lam, Colleen Douville, Anne Moore, Elizabeth Visco, David W. Newell,

Optical Imaging and Spectroscopy Techniques

The effects of anesthetic management on blood flow to the optic nerve have not been well-studied. The ophthalmic artery provides the majority of the blood supply to the optic nerve via several smaller branches. Retinal blood flow has been shown to react to carbon dioxide (CO2) similar to intracranial vessels, but insufficient data exist for the ophthalmic artery. The purpose of this study is to examine the CO2-reactivity of the ophthalmic artery. Eight healthy awake subjects aged 28 to 50 yr were tested for CO2-reactivity in the ophthalmic artery using transcranial Doppler (TCD) insonation of blood flow velocity (Vop), while simultaneously recording the Vop of the middle cerebral artery (Vmca) as an internal control. Vop and Vmca recordings were made under hypocapnic, normocapnic and hypercapnic conditions. The CO2-reactivity slope of Vmca was 3.27% per mmHg PaCO2. From normocapnia to hypercapnia, Vop did not change significantly (mean ± SD, 18 ± 4 cm·sec−1 to 18 ± 6 cm·sec−1), (endtidal CO2, et CO2, = 43 ± 5 mmHg to 53 ± 4 mmHg, respectively). In contrast, Vop increased significantly under hypocapnic conditions (etCO2 = 26 ± 4 mmHg) to 25 ± 5 cm·sec−1 (P < 0.05). The CO2-reactivity slope of Vop from normocapnia to hypocapnia was 2.57% per mmHg. This study demonstrates that Vop increases with hypocapnia, but is unaffected by hypercapnia. The anastomoses of the ophthalmic artery with the external carotid artery, which displays a relatively fixed resistance, may account for these findings.