Bronzwaer Anne-Sophie G T, Verbree Jasper, Stok Wim J, Daemen Mat J A P, van Buchem Mark A, van Osch Matthias J P, van Lieshout Johannes J
Department of Internal Medicine, Academic Medical Center, University of Amsterdam, Amsterdam, the Netherlands.
Laboratory for Clinical Cardiovascular Physiology, Center for Heart Failure Research, Academic Medical Center, University of Amsterdam, Amsterdam, the Netherlands.
J Appl Physiol (1985). 2017 Apr 1;122(4):877-883. doi: 10.1152/japplphysiol.00797.2016. Epub 2017 Jan 12.
Lower-body negative pressure (LBNP) has been proposed as a MRI-compatible surrogate for orthostatic stress. Although the effects of LBNP on cerebral hemodynamic behavior have been considered to reflect those of orthostatic stress, a direct comparison with actual orthostasis is lacking. We assessed the effects of LBNP (-50 mmHg) vs. head-up tilt (HUT; at 70°) in 10 healthy subjects (5 female) on transcranial Doppler-determined cerebral blood flow velocity (CBF) in the middle cerebral artery and cerebral perfusion pressure (CPP) as estimated from the blood pressure signal (finger plethysmography). CPP was maintained during LBNP but decreased after 2 min in response to HUT, leading to an ~15% difference in CPP between LBNP and HUT ( ≤ 0.020). Mean CBF initially decreased similarly in response to LBNP and for HUT, but, from minute 3 on, the decline became ~50% smaller ( ≤ 0.029) during LBNP. The reduction in end-tidal Pco partial pressure (Pet ) was comparable but with an earlier return toward baseline values in response to LBNP but not during HUT ( = 0.008). We consider the larger decrease in CBF during HUT vs. LBNP attributable to the pronounced reduction in Pet and to gravitational influences on CPP, and this should be taken into account when applying LBNP as an MRI-compatible orthostatic stress modality. Lower-body negative pressure (LBNP) has the potential to serve as a MRI-compatible surrogate of orthostatic stress but a comparison with actual orthostasis was lacking. This study showed that the pronounced reduction in end-tidal Pco together with gravitational effects on the brain circulation lead to a larger decline in cerebral blood flow velocity in response to head-up tilt than during lower-body negative pressure. This should be taken into account when employing lower-body negative pressure as MRI-compatible alternative to orthostatic stress.
下体负压（LBNP）已被提议作为一种与磁共振成像（MRI）兼容的模拟直立应激的方法。尽管LBNP对脑血流动力学行为的影响被认为反映了直立应激的影响，但缺乏与实际直立状态的直接比较。我们评估了10名健康受试者（5名女性）在LBNP（-50 mmHg）与头高位倾斜（HUT；70°）状态下，经颅多普勒测定的大脑中动脉脑血流速度（CBF）以及根据血压信号（手指体积描记法）估算的脑灌注压（CPP）的变化。在LBNP过程中CPP保持稳定，但在HUT后2分钟CPP下降，导致LBNP和HUT之间的CPP差异约为15%（P≤0.020）。平均CBF最初对LBNP和HUT的反应相似，但从第3分钟开始，LBNP期间CBF的下降幅度比HUT时小约50%（P≤0.029）。呼气末二氧化碳分压（PetCO₂）的降低情况相似，但LBNP时PetCO₂更早恢复到基线值，而HUT时则不然（P = 0.008）。我们认为，与LBNP相比，HUT期间CBF下降幅度更大是由于PetCO₂显著降低以及重力对CPP的影响，在将LBNP用作与MRI兼容的直立应激模式时应考虑到这一点。下体负压（LBNP）有潜力作为与MRI兼容的直立应激模拟方法，但缺乏与实际直立状态的比较。本研究表明，呼气末二氧化碳分压的显著降低以及重力对脑循环的影响导致头高位倾斜时脑血流速度的下降幅度大于下体负压时。在采用下体负压作为与MRI兼容的直立应激替代方法时应考虑到这一点。
