The postural reduction in middle cerebral artery blood velocity is not explained by PaCO2 |
| |
Authors: | R. V. Immink N. H. Secher C. M. Roos F. Pott P. L. Madsen J. J. van. Lieshout |
| |
Affiliation: | (1) Department of Anesthesiology, Academic Medical Center, University of Amsterdam, 22700, 1100, DE, Amsterdam, The Netherlands;(2) Department of Pulmonology, Academic Medical Center, University of Amsterdam, 22700, 1100, DE, Amsterdam, The Netherlands;(3) Departments of Internal Medicine, Medium Care Unit, F7-205, Academic Medical Center, University of Amsterdam, 22700, 1100, DE, Amsterdam, The Netherlands;(4) Department of Anesthesiology, Rigshospitalet, University of Copenhagen, Blegdamsvej 9, 2100 Copenhagen, Denmark;(5) The Copenhagen Muscle Research Center, Rigshospitalet, University of Copenhagen, Blegdamsvej 9, 2100 Copenhagen, Denmark |
| |
Abstract: | In the normocapnic range, middle cerebral artery mean velocity (MCA V mean) changes ∼ 3.5% per mmHg carbon-dioxide tension in arterial blood (PaCO2) and a decrease in PaCO2 will reduce the cerebral blood flow by vasoconstriction (the CO2 reactivity of the brain). When standing up MCA V mean and the end-tidal carbon-dioxide tension (PETCO2) decrease, suggesting that PaCO2 contributes to the reduction in MCA V mean. In a fixed body position, PETCO2 tracks changes in the PaCO2 but when assuming the upright position, cardiac output decreases and its distribution over the lung changes, while ventilation increases suggesting that PETCO2 decreases more than PaCO2. This study evaluated whether the postural reduction in PaCO2 accounts for the postural decline in MCA V mean. From the supine to the upright position, PETCO2, PaCO2, MCA V mean, and the near-infrared spectrophotometry determined cerebral tissue oxygenation (CO2Hb) were followed in seven subjects. When standing up, MCA V mean (from 65.3±3.8 to 54.6±3.3 cm s−1 ; mean ± SEM; P<0.05) and cO2Hb (−7.2±2.2 μmol l−1 ; P<0.05) decreased. At the same time, the ratio increased 49±14% (P<0.05) with the postural reduction in PETCO2 overestimating the decline in PaCO2 (−4.8±0.9 mmHg vs. −3.0±1.1 mmHg; P<0.05). When assuming the upright position, the postural decrease in MCA V mean seems to be explained by the reduction in PETCO2 but the small decrease in PaCO2 makes it unlikely that the postural decrease in MCA V mean can be accounted for by the cerebral CO2 reactivity alone. |
| |
Keywords: | Carbon dioxide Cardiac output Near-infrared spectroscopy Posture Ultrasonography Doppler Transcranial Ventilation |
本文献已被 PubMed SpringerLink 等数据库收录! |
|