The impact of increased mean airway pressure on contrast-enhanced MRI measurement of regional cerebral blood flow (rCBF), regional cerebral blood volume (rCBV), regional mean transit time (rMTT), and regional cerebrovascularresistance (rCVR) in human volunteers

Contrast-enhanced magnetic resonance imaging (MRI) measurement of cerebral perfusion is a diagnostic procedure increasingly gaining access to clinical practice not only in spontaneously breathing patients but also in mechanic ally ventilated patients. Effects of increased mean airway pressure on cere bral perfusion are entirely possible. Therefore, the present study used con tinuous positive airway pressure (CPAP) (12 cm H2O) to study the effects of increased mean airway pressure on cerebral perfusion in volunteers. CPAP s ignificantly reduced regional cerebral blood flow (rCBF) and regional cereb ral blood volume (rCBV) but increased regional mean transit time (rMTT) and regional, cerebrovascular resistance (rCVR). Active vasoconstriction (e.g. , arterial) and/or passive compression of capillary and/or venous vessel ar eas are the most likely underlying mechanisms. The number of interhemispher ic differences in rCBF, rCBV, rMTT, and rCVR found at baseline rose when me an airway pressure was increased. These results, although obtained in volun teers, should be taken into consideration for the interpretation of contras t-enhanced MRI perfusion measurements in mechanically ventilated patients w ith an increased positive airway pressure. Hum. Brain Mapping 11:214-722, 2 000. (C) 2000 Wiley-Liss, Inc.