Cerebrovascular reactivity evaluated by transcranial Doppler: reproducibility of different methods

Transcranial Doppler is routinely used to assess the cerebrovascular reactivity, despite scarce information on its reproducibility. We evaluated the reproducibility of cerebrovascular reactivity measurements by this method utilizing different vasodilatory and vasoconstrictor stimuli. The cerebrovascular reactivity was measured in 45 healthy volunteers during hypercapnia induced by inhalation of a mixture of 5% CO2 and 95% O-2, breath holding and rebreathing, and during hypocapnia induced by voluntary hyperventilation. Three sets of measurements were performed at times 0, 1, and 24 h to assess the within-observer short- and long-term reproducibility. The reproducibility was analyzed using the intraclass correlation coefficient. For the CO2 inhalation method, a good short-term (r(I) = 0.55; 95% CI = 0.39-0.68) and a good long-term (r(I) = 0.43; 95% CI = 0.25-0.59) reproducibility was found. For the breath-holding method a good shortterm agreement was found (r(I) = 0.41; 95% CI = 0.22-0.57), while the long-term reproducibility was poor (r(I) = 0.17; 95% CI = -0.03-0.36). Rebreathing showed a fair (r(I) = 0.31; 95% CI = 0.11-0.48) short-term and a poor (r(I) = 0.17; 95% CI = -0.03-0.36) long-term reproducibility. For voluntary hyperventilation, the short-term reproducibility was good (r(I) = 0.53; 95% CI = 0.36-0.66), and the long-term reproducibility was fair (r(I) = 0.31; 95% CI = 0.11-0.48). In our study, CO2 inhalation and voluntary hyperventilation had the highest reproducibility and should be preferred when assessing cerebral vasoreactivity, especially in follow-up studies.