Heterogeneous and lateralized cervical vascular responses to a 7-day head-down tilt bed rest

This study aimed to investigate cervical vessel hemodynamics during 7 days of -6° head-down tilt (HDT) bed rest (BR) and 5 days of recovery in 40 healthy males, focusing on bilateral analysis and dynamic temporal monitoring. Diameter, flow velocity, and blood flow volume (BFV) of bilateral common (CCAs), internal (ICAs), external carotid arteries and vertebral arteries (VAs) were measured at eight time points using ultrasound. Cervical vessels exhibited heterogeneous and lateralized responses. Left VA exhibited the most pronounced BFV and velocity fluctuations, with significant reductions during HDT and recovery to baseline post-HDT, while right VA remained stable. CCAs and ICAs had dynamic diameter and velocity changes, but stable BFVs. Left VA BFV reduction was significantly associated with right VA dominance, elevated heart rate, and increased mean arterial pressure at HDT 3 d. Despite stable total BFV, left VA BFV declined during BR, warranting further monitoring.