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Am J Physiol Heart Circ Physiol 291: H2018, 2006. First published April 28, 2006; doi:10.1152/ajpheart.00390.2006
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LETTERS TO THE EDITOR

Cerebral Autoregulation and CO2 Responsiveness of the Brain

Rogier V. Immink

Department of Anesthesiology
Cardiovascular Research Institute Amsterdam
Academic Medical Center/University of Amsterdam
Amsterdam, The Netherlands

Niels H. Secher

Copenhagen Muscle Research Center
Department of Anesthesia
Rigshospitalet
University of Copenhagen
Copenhagen, Denmark

Johannes J. van Lieshout

Medical Care Unit/Department of Internal Medicine
Cardiovascular Research Institute Amsterdam
Academic Medical Center/University of Amsterdam
Amsterdam 1105 AZ, The Netherlands
e-mail: j.jvanlieshout{at}amc.uva.nl

The following is the abstract of the article discussed in the subsequent letter:

We used a longitudinal study design (gestational weeks 8, 15, 22, 29, and 36 and 12 wk postpartum ) to investigate the effect of normal pregnancy on cerebral autoregulation and pressor response. Blood flow velocities in the right internal carotid artery, end-tidal CO2, and mean arterial pressure (MAP) were simultaneously and continuously recorded in 16 healthy pregnant women during standardized hyperventilation and handgrip. Blood flow velocities were recorded using Doppler ultrasound sampled beat by beat using the ECG signal. The results demonstrate that the vasoconstrictor response to hyperventilation is unchanged during pregnancy. During standardized handgrip, MAP showed a statistically significant increase during pregnancy that did not affect cerebral blood flow. A statistically significant reduction in the MAP response to handgrip was seen in week 36. In conclusion, pregnancy has no impact on cerebral autoregulation. There is an impact on the pressor response resulting in a blunted reaction at week 36, probably caused by a fall in the baroreflex set point.

To the Editor: Bergersen et al. (1) describe the effect of normal pregnancy, from 8 wk gestation to 3 mo postpartum, on the pressor response to static handgrip and changes in PCO2 for evaluation of cerebral autoregulation. Changes in carotid artery blood velocity (FV) are related to mean arterial pressure and end-tidal PCO2 (PETCO2), but to manipulate PETCO2 to gauge cerebral autoregulation is problematic. The tendency of cerebral blood flow (CBF) to remain constant over a range of systemic blood pressures is termed cerebral autoregulation, for which both local mechanisms and autonomic control participate. Forbes (2) demonstrated that pial vessels of the cat are under both vasomotor and chemical control (4). The cerebrovascular responsiveness to arterial PCO2 or PETCO2 (3), as estimated by CBF or FV, operates independently from cerebral autoregulation and is known as the CO2 reactivity of the brain. Cerebral autoregulation and its CO2 reactivity are two distinct mechanisms that interact in a complex way (5, 6). For example, the limits of arterial blood pressure within which cerebral autoregulation operates are modified by the PCO2 (7). What Bergersen et al. (1) show elegantly is not that cerebral autoregulation but that cerebral CO2 reactivity is preserved during and after pregnancy.

REFERENCES

  1. Bergersen TK, Hartgill TW, and Pirhonen J. Cerebrovascular response to normal pregnancy: a longitudinal study. Am J Physiol Heart Circ Physiol 290: H1856–H1861, 2006.[Abstract/Free Full Text]
  2. Forbes HS. Cerebral circulation. 1. Observation and measurement of pial vessels. Arch Neurol Psychiat 19: 751–761, 1928.
  3. Immink RV, Secher NH, Roos CM, Pott F, Madsen PL, and Van Lieshout JJ. The postural reduction in middle cerebral artery blood velocity is not explained by PaCO2. Eur J Appl Physiol 96: 609–614, 2006.[CrossRef][Web of Science][Medline]
  4. Lennox WG and Gibbs EL. Blood flow in brain and leg of man, and changes induced by alteration of blood gases. J Clin Invest 11: 1155–1177, 1932.[Medline]
  5. Park CW, Sturzenegger M, Douville CM, Aaslid R, and Newell DW. Autoregulatory response and CO2 reactivity of the basilar artery. Stroke 34: 34–39, 2003.[Abstract/Free Full Text]
  6. Van Lieshout JJ and Wieling W. Perfusion of the brain: a matter of interactions. J Physiol 551: 402, 2003.[Free Full Text]
  7. Van Lieshout JJ, Wieling W, Karemaker JM, and Secher NH. Syncope, cerebral perfusion, and oxygenation. J Appl Physiol 94: 833–848, 2003.[Abstract/Free Full Text]



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 Am. J. Physiol. Heart Circ. Physiol.Home page
T. K. Bergersen, T.W. Hartgill, and J. Pirhonen
REPLY
Am J Physiol Heart Circ Physiol, October 1, 2006; 291(4): H2019 - H2019.
[Full Text] [PDF]

This Article
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