[Changes of human cerebral blood flow velocity and blood oxygen saturation under lower body negative pressure in upright seated position].

Objective. To investigate the effect of lower body negative pressure (LBNP) in upright seated position on cerebral blood flow velocity, heart rate (HR), and blood oxygen saturation (SaO2) in human. Method. Fifteen young men were selected as subjects. Blood flow velocity in middle cerebral artery (VMCA), HR and SaO2 were measured at 0.5, 1, 2, 3, 4, and 5 min during LBNP and 1, 3, 5 min after -4.00 kPa and -6.67 kPa LBNP in upright seated position respectively. Result. Under -4.00 kPa LBNP, VMCA slowed down at 4, 5 min during LBNP (P<0.05), and HR speeded up at 3, 4, 5 min during LBNP (P<0.05). There were no significant changes of SaO2. Under -6.67 kPa LBNP, VMCA became slow at 2, 3 min (P<0.05), and at 4 and 5 min (P<0.01) during LBNP. At 1 min after release of LBNP, VMCA did not recover, after which it recovered to control level. HR significantly increased (P<0.01) and SaO2 decreased at 5 min (P<0.05) during LBNP. Conclusion. LBNP can cause blood pooling in lower body so that VMCA and brain blood volume decrease. Then it causes loss of consciousness. The results of this experiment may provide experimental data for diagnosis of flight syncope and orthostatic intolerance.