Measurement of vasomotor reserve in the transcranial Doppler-CO(2) test using an ultrasound contrast agent (Levovist).
BACKGROUND AND PURPOSE
Determination of vasomotor reserve (VMR) with the transcranial Doppler-CO(2) (TCD-CO(2)) test is used to assess the risk of impending cerebral ischemia in patients with high-grade stenosis or occlusion of the internal carotid artery. In patients with a poor temporal window, however, this examination is limited. The aim of this study therefore was to examine whether the use of an ultrasound contrast agent (USCA) influences the results of the TCD-CO(2) test.


METHODS
In the first part of the study, 6 control subjects and 20 patients were examined with the TCD-CO(2) test. The VMR was determined first without the application of a contrast agent and then with continuous infusion of an USCA (Levovist, 300 mg/mL, 1 mL/min). In the second part of the study, 2 tests without USCA were performed in each of 13 patients and 2 tests with USCA infusion were performed in each of 12 patients. Statistical analysis included differences between the VMR determined with the 2 comparative measurements (VMR), the mean (M(VMR)), and SD.


RESULTS
Based on the mean difference, the TCD-CO(2) test produced the same results with and without USCA (M(VMR) 1.8%), although the differences showed a wide distribution (2 SDs, +/-20.7%). Similar spreads were seen in repeated determinations of VMR in the same patient without USCA (2 SDs, +/-20.0%), whereas the distribution under continuous USCA infusion was considerably smaller (2 SDs, +/-8.2%).


CONCLUSIONS
The TCD-CO(2) test can be performed with continuous infusion of an USCA without influencing the results. Even with a good temporal window, the results of the TCD-CO(2) test show better reproducibility and thus better reliability if an USCA is used.