Peters, Paul; (1995) The influence of carotid disease on cerebral vascular autoregulation and cerebral vascular reactivity to hypercapnia. Masters thesis (M.S), UCL (University College London).

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Abstract

Cerebral vascular reactivity to hypercapnia, assessed using transcranial Doppler ultrasonography of middle cerebral artery blood flow velocity, is used to assess the extent of cerebral blood flow reserve. It has been assumed that in patients with carotid disease a reduced reactivity to hypercapnia can be interpreted as indicating reduced cerebral perfusion with reduced autoregulatory capacity. This relationship between reactivity to hypercapnia and autoregulation in the cerebral vasculature is tested. A method for the non-invasive measurement of cerebral vascular autoregulation to changes in blood pressure is described and this method is used to assess autoregulation in a group of normal subjects. Hypercapnia is shown to obtund autoregulation whereas hypocapnia is shown to exaggerate cerebral vascular autoregulation to changes in blood pressure. It is shown that volitional respiration significantly increases middle cerebral artery blood flow velocity. Cerebral vascular reactivity to hypercapnia is measured in patients with carotid disease and is shown to be reduced in the presence of internal carotid artery occlusion. It is also shown that whilst some patients with severe carotid artery disease have reduced cerebral vascular reactivity to hypercapnia, the presence of severe carotid artery disease per se does not predict a reduced reactivity index. In the presence of internal carotid artery occlusion an increased degree of contralateral internal carotid artery stenosis reduces ipsilateral cerebral vascular reactivity to hypercapnia. The relationship between cerebral vascular autoregulation and cerebral vascular reactivity to hypercapnia is tested in a group of subjects with severe carotid disease. The methods described for the measurement of cerebral vascular autoregulation and cerebral vascular reactivity to hypercapnia are employed to measure both parameters in each individual in the group and it is shown that there is a strong correlation between the presence of reduced cerebral vascular reactivity to hypercapnia and reduced cerebral vascular autoregulation to pressure change.

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