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Circulatory Response to Blood Gas Perturbations in Vasospasm

From the Ophthalmology Department of the University Clinic Basel, Basel, Switzerland.

PURPOSE. To investigate the response of the optic nerve head and the choroidal circulation to blood gas perturbations in otherwise healthy subjects with a history of cold hands.

METHODS. Thirty-five healthy subjects were selected and grouped according to the related history of cold hands. All 12 selected male subjects, aged 21 to 38 years (mean ± SD = 28 ± 5.2 years) had a negative history of cold hands. Female subjects were almost equally divided between the groups with a negative (11 subjects, aged 18–36 years; mean, 25.7 ± 5.5) or positive (12 subjects, aged 19–45 years; mean, 25 ± 6.8) history of cold hands. Blood gas perturbations were created by having subjects breath a gas mixture consisting of 21% O₂, 74% N₂, and 5% CO₂. The partial pressures pCO₂ and pO₂ were continuously monitored transcutaneously. Choroidal and optic nerve head blood flow response was evaluated by means of laser Doppler flowmetry.

RESULTS. Systolic and diastolic blood pressure (SBP/DBP at baseline, three-group average: 111.2/71.9 mm Hg), heart rate (HR; 70.3 bpm), and intraocular pressure (IOP; 14.7 mm Hg) increased during the blood gas perturbation phase (123.1/77.7 mm Hg, 78.5 bpm, and 15.6 mm Hg, respectively) and returned to baseline in the recovery phase (109.9/73.4 mm Hg, 69.5 bpm, and 13.5 mm Hg, respectively). There was no difference between groups (one-way ANOVA of the percentage change from baseline for SBP, P = 0.75; DBP, P = 0.36; HR, P = 0.95; and IOP, P = 0.72). pCO₂ increased from 5.52 to 6.59 kPa and returned to 5.50 kPa. pO₂ increased from 10.64 to 13.12 kPa and returned to 10.73 kPa. Again, there was no difference between groups (one-way ANOVA for the percentage change: pCO₂, P = 0.17; pO₂, P = 0.78). In the women with vasospasm, optic nerve head blood flow increased 17.1% and the choroidal blood flow decreased –3.6%, whereas in the women and men without vasospasm the optic nerve head blood flow decreased –5.8% and –4.8%, and the choroidal blood flow increased 13.3% and 18.3%, respectively (two-way ANOVA interaction; P = 0.001).

CONCLUSIONS. The pCO₂ increase was accompanied by a pO₂ increase. Blood pressure and HR increased comparably in all groups, indicating sympathetic arousal. The women with vasospasm demonstrated an inverse response pattern of choroidal and optic nerve head circulation to blood gas perturbation compared with the women without vasospasm and compared with the men.

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