HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) All Versions of this Article: 287/3/R627    most recent 00384.2003v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (4) Citing Articles via Google Scholar Google Scholar Articles by Edwards, M. R. Articles by Hughson, R. L. Search for Related Content PubMed PubMed Citation Articles by Edwards, M. R. Articles by Hughson, R. L.

ENVIRONMENTAL, EXERCISE AND RESPIRATORY PHYSIOLOGY

Two-breath CO₂ test detects altered dynamic cerebrovascular autoregulation and CO₂ responsiveness with changes in arterial PCO₂

Cardiorespiratory and Vascular Dynamics Laboratory, Faculty of Applied Health Sciences, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1

Submitted 11 July 2003 ; accepted in final form 16 March 2004

The new two-breath CO₂ method was employed to test the hypotheses that small alterations in arterial PCO₂ had an impact on the magnitude and dynamic response time of the CO₂ effect on cerebrovascular resistance (CVRi) and the dynamic autoregulatory response to fluctuations in arterial pressure. During a 10-min protocol, eight subjects inspired two breaths from a bag with elevated PCO₂, four different times, while end-tidal PCO₂ was maintained at three levels: hypocapnia (LoCO₂, 8 mmHg below resting values), normocapnia, and hypercapnia (HiCO₂, 8 mmHg above resting values). Continuous measurements were made of mean blood pressure corrected to the level of the middle cerebral artery (BP_MCA), PCO₂ (estimated from expired CO₂), and mean flow velocity (MFV, of the middle cerebral artery by Doppler ultrasound), with CVRi = BP_MCA/MFV. Data were processed by a system identification technique (autoregressive moving average analysis) with gain and dynamic response time of adaptation estimated from the theoretical step responses. Consistent with our hypotheses, the magnitude of the PCO₂-CVRi response was reduced from LoCO₂ to HiCO₂ [from –0.04 (SD 0.02) to –0.01 (SD 0.01) (mmHg·cm^–1·s)·mmHg PCO₂^–1] and the time to reach 95% of the step plateau increased from 12.0 ± 4.9 to 20.5 ± 10.6 s. Dynamic autoregulation was impaired with elevated PCO₂, as indicated by a reduction in gain from LoCO₂ to HiCO₂ [from 0.021 ± 0.012 to 0.007 ± 0.004 (mmHg·cm^–1·s)·mmHg BP_MCA^–1], and time to reach 95% increased from 3.7 ± 2.8 to 20.0 ± 9.6 s. The two-breath technique detected dependence of the cerebrovascular CO₂ response on PCO₂ and changes in dynamic autoregulation with only small deviations in estimated arterial PCO₂.

Doppler ultrasound; brain blood flow; autoregressive moving average; carbon dioxide

This article has been cited by other articles:

				D. Fischer, P. Arbeille, J. K. Shoemaker, D. D. O'Leary, and R. L. Hughson Altered hormonal regulation and blood flow distribution with cardiovascular deconditioning after short-duration head down bed rest J Appl Physiol, December 1, 2007; 103(6): 2018 - 2025. [Abstract] [Full Text] [PDF]

				J. E Naschitz and I. Rosner Orthostatic hypotension: framework of the syndrome Postgrad. Med. J., September 1, 2007; 83(983): 568 - 574. [Abstract] [Full Text] [PDF]

				R. B. Panerai, P. J. Eames, and J. F. Potter Multiple coherence of cerebral blood flow velocity in humans Am J Physiol Heart Circ Physiol, July 1, 2006; 291(1): H251 - H259. [Abstract] [Full Text] [PDF]

				R. B. Panerai, M. Moody, P. J. Eames, and J. F. Potter Cerebral blood flow velocity during mental activation: interpretation with different models of the passive pressure-velocity relationship J Appl Physiol, December 1, 2005; 99(6): 2352 - 2362. [Abstract] [Full Text] [PDF]

				S. Krishnamurthy, X. Wang, D. Bhakta, E. Bruce, J. Evans, T. Justice, and A. Patwardhan Dynamic cardiorespiratory interaction during head-up tilt-mediated presyncope Am J Physiol Heart Circ Physiol, December 1, 2004; 287(6): H2510 - H2517. [Abstract] [Full Text] [PDF]