Introduction: Cerebral autoregulation (CA) has been understood for over 50 years to maintain constant cerebral blood flow (CBF) over a wide range of arterial blood pressures (60-150 mmHg), and blood volumes. The original work, which published this relationship, however, was derived from a limited number of studies focused primarily on clinical populations. Since that time, it has been applied to healthy individuals and is a mainstay of almost all physiology textbooks. Recent evidence, however, has suggested that CBF in healthy individuals is not independent of alterations in blood pressure and volume, indicating a possible absence of cerebral autoregulation. Lower body negative pressure (LBNP) and lower body positive pressure (LBPP) are two techniques that involve the non-invasive manipulation of blood volume through the application of either positive or negative pressure on the lower limbs. Application of LBNP works to reduce upper body blood volume, while the opposite effect occurs with LBPP. In this study, through the use of both LBNP and LBPP we aimed to investigate the effects of altered blood volume on CBF in healthy individuals.



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