Cerebral autoregulation and CO2 responsiveness of the brain.

response to normal pregnancy: a longitudinal study. 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 CO 2, 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. Cerebral Autoregulation and CO 2 Responsiveness of the Brain 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 PCO 2 for evaluation of cerebral autoregulation. Changes in carotid artery blood velocity (FV) are related to mean arterial pressure and end-tidal PCO 2 (PET CO 2), but to manipulate PET CO 2 to gauge cerebral autoregulation is problematic. The tendency of cere-bral 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 cerebro-vascular responsiveness to arterial PCO 2 or PET CO 2 (3), as estimated by CBF or FV, operates independently from cerebral autoregulation and is known as the CO 2 reactivity of the brain. Cerebral autoregulation and its CO 2 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 PCO 2 (7). What Bergersen et al. (1) show elegantly is not that cerebral auto-regulation but that cerebral CO 2 reactivity is preserved during and after pregnancy. Lieshout JJ. The postural reduction in middle cerebral artery blood velocity is not explained by PaCO 2. Blood flow in brain and leg of man, and changes …