Cerebrovascular Reserve Capacity (CRC) in Carotid Artery Disease: A Routine Test in Selection for Surgical Treatment?

Abstract

An increase of arterial carbon dioxide (CO2) partial pressure induces an increase of cerebral blood flow by dilatation of the resistance vessels. By the Transcranial Doppler sonographic technique (TCD) blood flow velocity as a correlate of flow volume can be measured within the great basal intracranial arteries. We investigated 8 patients with an internal carotid artery occlusion or high-grade stenosis and 5 cerebrovascular diseased patients without extracranial stenosis. 12 healthy volunteers and patients without vascular disease served as the control group. Blood flow velocities in the middle cerebral arteries were evaluated before and after 5 minutes of breathing a 5% CO2 gas mixture. In a prestudy the end tidal pCO2 was monitored during this procedure. As a result of the close parallelity of pCO2 increase in the prestudy group we planned to standardize the CO2 reactivity tests without consideration of the individual pCO2 values. The CO2 inhalation provoked a flow velocity increase of at least 20% in the control subjects (47.1 +/- 17.3%). The vascular diseased without extracranial stenosis responded with 34.8 +/- 17.4% (minimum: 23.5%, n. s.). The CO2 reactivity in cases of occlusion or greater than 50% stenosis was significantly decreased (p less than 0.001) both when considering only the affected sides (12.4 +/- 7.5%, maximum: 20%) and when including the non affected sides (22.6 +/- 15.0%). It is concluded that the CO2 reactivity test is a simple and valid method to evaluate the cerebrovascular reserve capacity in any case of uncertainty about the benefits of surgical treatment of a carotid stenosis. In future this technique might become one fundamental argument beside others in selecting adequate treatment.

Current understanding of chronic total occlusion of the internal carotid artery (Review)

“…In CTO of the ICA, CVR is reduced; this impairment has been associated with increased risk of ischemic events and may be useful for stroke risk stratification ( 30 ). In normal cases, CVR is unimpaired (stage 0) ( 31 ). CVR impairment may be divided into three stages: In stage I hemodynamic failure, autoregulatory compensatory vasodilation is still able to maintain normal CBF, and the oxygen extraction fraction (OEF) remains normal.…”

Decreased transcranial Doppler carbon dioxide reactivity is associated with disordered cerebral metabolism in patients with internal carotid artery stenosis

“…[6][7][8] An ipsilaterally lowered CO 2 reactivity can be found in patients with severe stenosis of the ICA, especially when the contralateral ICA is also obstructed. [9][10][11][12][13][14] The CO 2 reactivity might be superior to the measured degree of ICA stenosis alone as an indicator of the hemodynamic consequences of ICA stenosis, because CO 2 reactivity also depends on the quality of the collateral circulation. As illustration of the clinical significance of the CO 2 reactivity, especially in patients with low-flow infarctions, patients with chronic retinal ischemia or hypostatic TIAs have a lowered CO 2 reactivity.…”