[Changes of cervical blood flow in subjects with different tolerances to -30 degrees head-down bed rest]

In order to investigate characteristics of cervical blood flow in subjects with different tolerances to head-down tilt (HDT), 40 healthy men (aged 26-35 years) participated in the test of -30 degrees HDT for 45 min. During the test, mean blood flow velocities, diameters and blood flow volume of common carotid artery (CCA), Internal carotid artery (ICA), Internal jugular vein (IJV) were measured with color Doppler echogram. The results showed that there have different changes of in-flow of ICA and out-flow of UV between the adaptive subjects (n=33) and the inadaptive subjects (n=7). In the adaptive group, the cerebral blood flow volume during HDT, did not change from that during horizontal supine position. However, in the inadaptive group in-flow of ICA increased and out-flow of IJV decreased significantly during HDT as compared with those during horizontal supine position.