A new two-breath technique for extracting the cerebrovascular response to arterial carbon dioxide

• Published in: American journal of physiology. Regulatory, integrative and comparative physiology Vol. 284; no. 3; pp. 853 - R859
• Main Authors: Edwards, Michael R, Topor, Zigniew L, Hughson, Richard L
• Format: Journal Article
• Language: English
• Published: United States 01.03.2003
• Subjects: Adult; Blood Flow Velocity; Blood Pressure; Breath Tests - methods; Carbon Dioxide - blood; Cerebral Arteries; Cerebrovascular Circulation - physiology; Female; Humans; Inhalation; Male; Vascular Resistance
• ISSN: 0363-6119; 1522-1490
• DOI: 10.1152/ajpregu.00601.2002

Cardiorespiratory and Vascular Dynamics Laboratory, Faculty of Applied Health Sciences, University of waterloo, Waterloo, Ontario, Canada N2L 3G1 Cerebrovascular autoregulation is evaluated from spontaneous fluctuations in mean flow velocity (MFV) by transcranial Doppler ultrasound of the middle cerebral artery (MCA) with respect to changes in arterial blood pressure (BP MCA ), but the effects of spontaneous fluctuations in arterial P CO 2 on MFV have been largely ignored. Autoregressive moving average analysis (ARMA), a closed-loop system identification technique, was applied to data from nine healthy subjects during spontaneous breathing, during inspiration of 10% CO 2 for two breaths once per minute for 4 min, and during sustained breathing of 7% CO 2 . Cerebrovascular resistance index (CVRi) was calculated (CVRi = BP MCA /MFV). Reliable estimates of gain for BP MCA  MFV were obtained for spontaneous breathing and the two-breath method. In contrast, reliable gain estimates for P CO 2  MFV or P CO 2  CVRi were achieved only under the two-breath method. P CO 2  MFV gain was smaller with the two-breath method than during sustained 7% CO 2 ( P  < 0.05). BP MCA was elevated by 7% CO 2 but not by the two-breath method. The closed-loop model provides insight into interactions between BP MCA and P CO 2 on cerebrovascular control, but reliable solutions for P CO 2 effects with ARMA analysis require perturbation by the two-breath method. autoregressive moving average analysis modeling; arterial carbon dioxide partial pressure; Doppler ultrasound; cerebral blood flow; autoregulation