Cerebrovascular reactivity evaluated by transcranial Doppler: Reproducibility of different methods

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