Influence of upper body position on middle cerebral artery blood velocity during continuous positive airway pressure breathing
Continuous positive airway pressure (CPAP) is a treatment modality for pulmonary oxygenation difficulties. CPAP impairs venous return to the heart and, in turn, affects cerebral blood flow (CBF) and augments cerebral blood volume (CBV). We considered that during CPAP, elevation of the upper body would prevent a rise in CBV, while orthostasis would challenge CBF. To determine the body position least affecting indices of CBF and CBV, the middle cerebral artery mean blood velocity (MCA Vmean) and the near-infrared spectroscopy determined frontal cerebral hemoglobin content (cHbT) were evaluated in 11 healthy subjects during CPAP at different body positions (15° head-down tilt, supine, 15°, 30° and 45° upper body elevation). In the supine position, 10 cmH2O of CPAP reduced MCA Vmean by 9 ± 3% and increased cHbT by 4 ± 2 μmol/L (mean ± SEM); (P < 0.05). In the head-down position, CPAP increased cHbT to 13 ± 2 μmol/L but left MCA Vmean unchanged. Upper body elevation by 15° attenuated the CPAP associated reduction in MCA Vmean (−7 ± 2%), while cHbT returned to baseline (1 ± 2 μmol/L). With larger elevation of the upper body MCA Vmean decreased progressively to −17 ± 3%, while cHbT remained unchanged from baseline. These results suggest that upper body elevation by ∼15° during 10 cmH2O CPAP prevents an increase in cerebral blood volume with minimal effect on cerebral blood flow.
KeywordsTranscranial Doppler Near-infrared spectroscopy Posture Head-down tilt
- Dellinger RP, Carlet JM, Masur H, Gerlach H, Calandra T, Cohen J, Gea-Banacloche J, Keh D, Marshall JC, Parker MM, Ramsay G, Zimmerman JL, Vincent JL, Levy MM (2004) Surviving Sepsis Campaign guidelines for management of severe sepsis and septic shock. Crit Care Med 32:858–873PubMedCrossRefGoogle Scholar
- Droste DW, Ludemann P, Anders F, Kemeny V, Thomas M, Krauss JK, Ringelstein EB (1999) Middle cerebral artery blood flow velocity, end-tidal pCO2 and blood pressure in patients with obstructive sleep apnea and in healthy subjects during continuous positive airway pressure breathing. Neurol Res 21:737–741PubMedGoogle Scholar
- Harms MP, Wesseling KH, Pott F, Jenstrup M, van Goudoever J, Secher NH, van Lieshout JJ (1999) Continuous stroke volume monitoring by modelling flow from non-invasive measurement of arterial pressure in humans under orthostatic stress. Clin Sci (Lond) 97:291–301Google Scholar
- Kolbitsch C, Lorenz IH, Hormann C, Schocke M, Kremser C, Zschiegner F, Felber S, Benzer A (2000) The impact of increased mean airway pressure on contrast-enhanced MRI measurement of regional cerebral blood flow (rCBF), regional cerebral blood volume (rCBV), regional mean transit time (rMTT), and regional cerebrovascular resistance (rCVR) in human volunteers. Hum Brain Mapp 11:214–222PubMedCrossRefGoogle Scholar
- Ricksten SE, Bengtsson A, Soderberg C, Thorden M, Kvist H (1986) Effects of periodic positive airway pressure by mask on postoperative pulmonary function. Chest 86:774–781Google Scholar