Correction for Blood Pressure Improves Correlation between Cerebrovascular Reactivity Assessed by Breath Holding and 6% CO2 Breathing

Background Changes in cerebral blood flowvelocity to hypercapniaare associated with changes in systemic blood pressure (BP). These confounding BP-dependent changes in cerebral blood flowvelocity cause misinterpretation of cerebrovascular reactivity (CVR) results. The objective of the study was to determine the relationship between CVR assessed by breathholding and 6% CO 2 breathingafter correcting for BP-dependent changes in cerebral blood flowvelocity. Methods In 33 patients of uncomplicated type 2 diabetes mellitus, CVR was assessed as percentage changes in cerebral blood flowvelocity and cerebrovascular conductance index. Results Percentage change in cerebral blood flowvelocity during breathholding was positively correlated with that of during 6% CO 2 breathing( r = .35; P = .0448). CVR during breathholding and 6% CO 2 breathingwere better correlated when expressed as percentage changes in cerebrovascular conductance index ( r = .49; P = .0040). Similarly, breath- holding testresults expressed as percentage changes in cerebral blood flowvelocity correctly identified only 37.5% of the poor reactors to 6% CO 2 breathing. However, when the breath- holding testresults were expressed as percentage changes in cerebrovascular conductance index, 62.5% of the poor reactors to 6% CO 2 breathingwere correctly identified indicating a better agreement between the test results obtained by the 2 methods. Conclusion Cerebrovascular response to breathholding is better correlated with that of 6% CO 2 breathingwhen changes in cerebral blood flowvelocity were corrected for associated changes in BP.