caa a22 4500 467941319 CHVBK 20180406153013.0 cr unu---uuuuu 170328e20060301xx s 000 0 eng 10.1007/s00421-006-0136-6 doi (NATIONALLICENCE)springer-10.1007/s00421-006-0136-6 The postural reduction in middle cerebral artery blood velocity is not explained by PaCO2 [Elektronische Daten] [R. Immink, N. Secher, C. Roos, F. Pott, P. Madsen, J. Lieshout] 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 $$(\dot {Q})$$ decreases and its distribution over the lung changes, while ventilation $$(\dot {V}_{{\rm E}})$$ 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, $$\dot {V}_{{\rm E}},$$ $$\dot {Q},$$ 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±3.3cms−1 ; mean ± SEM; P<0.05) and cO2Hb (−7.2±2.2μmoll−1 ; P<0.05) decreased. At the same time, the $$\dot {V}_{{\rm E}}/\dot {Q}$$ ratio increased 49±14% (P<0.05) with the postural reduction in PETCO2 overestimating the decline in PaCO2 (−4.8±0.9mmHg vs. −3.0±1.1mmHg; 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. Springer-Verlag, 2006 Carbon dioxide nationallicence Cardiac output nationallicence Near-infrared spectroscopy nationallicence Posture nationallicence Ultrasonography nationallicence Doppler nationallicence Transcranial nationallicence Ventilation nationallicence Immink R. Department of Anesthesiology, Academic Medical Center, University of Amsterdam, 22700, 1100, Amsterdam, DE, The Netherlands aut Secher N. Department of Anesthesiology, Rigshospitalet, University of Copenhagen, Blegdamsvej 9, 2100, Copenhagen, Denmark aut Roos C. Department of Pulmonology, Academic Medical Center, University of Amsterdam, 22700, 1100, Amsterdam, DE, The Netherlands aut Pott F. The Copenhagen Muscle Research Center, Rigshospitalet, University of Copenhagen, Blegdamsvej 9, 2100, Copenhagen, Denmark aut Madsen P. The Copenhagen Muscle Research Center, Rigshospitalet, University of Copenhagen, Blegdamsvej 9, 2100, Copenhagen, Denmark aut Lieshout J. Departments of Internal Medicine, Medium Care Unit, F7-205, Academic Medical Center, University of Amsterdam, 22700, 1100, Amsterdam, DE, The Netherlands aut European Journal of Applied Physiology Springer-Verlag 96/5(2006-03-01), 609-614 1439-6319 96:5<609 2006 96 421 https://doi.org/10.1007/s00421-006-0136-6 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/s00421-006-0136-6 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Immink R. Department of Anesthesiology, Academic Medical Center, University of Amsterdam, 22700, 1100, Amsterdam, DE, The Netherlands aut NATIONALLICENCE 700 1- Secher N. Department of Anesthesiology, Rigshospitalet, University of Copenhagen, Blegdamsvej 9, 2100, Copenhagen, Denmark aut NATIONALLICENCE 700 1- Roos C. Department of Pulmonology, Academic Medical Center, University of Amsterdam, 22700, 1100, Amsterdam, DE, The Netherlands aut NATIONALLICENCE 700 1- Pott F. The Copenhagen Muscle Research Center, Rigshospitalet, University of Copenhagen, Blegdamsvej 9, 2100, Copenhagen, Denmark aut NATIONALLICENCE 700 1- Madsen P. The Copenhagen Muscle Research Center, Rigshospitalet, University of Copenhagen, Blegdamsvej 9, 2100, Copenhagen, Denmark aut NATIONALLICENCE 700 1- Lieshout J. Departments of Internal Medicine, Medium Care Unit, F7-205, Academic Medical Center, University of Amsterdam, 22700, 1100, Amsterdam, DE, The Netherlands aut NATIONALLICENCE 773 0- European Journal of Applied Physiology Springer-Verlag 96/5(2006-03-01), 609-614 1439-6319 96:5<609 2006 96 421 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer