Chapter 6 hypercapnia, hyperventilation, hypertonic glucose and administration of pa- paverine. Therefore the assumption of constant vessel diameter seems legitimate for this study. Conclusion Studying dCA and CO2R during CPB is feasible by changing pump flow at a 6/min rate. Induced blood pressure variations result in high coherence for trans- fer function analysis, indicating that ABP and CBFV are strongly linearly related. Moreover, increased arterial CO2levels clearly lead to impaired cerebral auto- regulation. Future studies that use TCD and NIRS to evaluate dCA and CO2R will hopefully clarify optimal perfusion strategies for various patient populations scheduled for operations involving CPB. Acknowledgements The authors thank Prof. R.B. Panerai (University of Leicester, UK) for his valu- able contributions to the manuscript. References 1. Aaslid R. Cerebral autoregulation and vasomotor reactivity.Front Neurol Neurosci21: 216-228, 2006. 2. Aaslid R, Lash SR, Bardy GH, Gild WH, and Newell DW. Dynamic pressure-flow velocity relationships in the human cerebral circulation. Stroke34: 1645-1649, 2003. 3. Aaslid R, Lindegaard KF, Sorteberg W, and Nornes H. Cerebral autore- gulation dynamics in humans.Stroke20: 45-52, 1989. 4. Ainslie PN, Celi L, McGrattan K, Peebles K, and Ogoh S. Dynamic cerebral autoregulation and baroreflex sensitivity during modest and se- vere step changes in arterial PCO2.Brain Res1230: 115-124, 2008. 5. Birch AA, Dirnhuber MJ, Hartley-Davies R, Iannotti F, and Neil-Dwyer G. Assessment of autoregulation by means of periodic changes in blood pressure.Stroke26: 834-837, 1995. 6. Bishop CC, Powell S, Rutt D, and Browse NL. Transcranial Doppler measurement of middle cerebral artery blood flow velocity: a validation study.Stroke17: 913-915, 1986. 7. Brady K, Joshi B, Zweifel C, Smielewski P, Czosnyka M, Easley RB, and Hogue CW, Jr. Real-Time Continuous Monitoring of Cerebral Blood 116
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