Abstract：
Blood volume shifts during postural adjustment lead to irregular distension of the internal jugular vein (IJV). In microgravity, distension may contribute to flow stasis and thromboembolism, though the regional implications and associated risk remain unexplored. We characterized regional differences in IJV volume distension and flow complexity during progressive head-down tilt (HDT) (0°, -6°, -15°, -30°) using conventional ultrasound and vector flow imaging. We also evaluated low-pressure thigh cuffs (40 mmHg) as a fluid shifting countermeasure during -6° HDT. Total IJV volume expanded 139 ± 95% from supine position (4.6 ± 2.7 mL) to -30° HDT (10.3 ± 5.0 mL). Blood flow profiles had greater vector uniformity at the cranial IJV region (P < 0.01) and became more dispersed with increasing tilt (P < 0.01). Qualitatively, flow was more uniform throughout the IJV during its early flow cycle phase and more disorganized during late flow phase. This disorganized flow was accentuated closer to the vessel wall, near the caudal region, and during greater HDT. Low-pressure thigh cuffs during -6° HDT decreased IJV volume at the cranial region (-12 ± 15%; P < 0.01) but not the caudal region (P = 0.20), although flow uniformity was unchanged (both regions, P > 0.25). We describe a distensible IJV accommodating large volume shifts along its length. Prominent flow dispersion was primarily found at the caudal region, suggesting multidirectional blood flow. Thigh cuffs appear effective for decreasing IJV volume but effects on flow complexity are minor. Flow complexity along the vessel length is likely related to IJV distension during chronic volume shifting and may be a precipitating factor for flow stasis and future thromboembolism risk.NEW & NOTEWORTHY The internal jugular vein (IJV) facilitates cerebral outflow and is sensitive to volume shifts. Concerns about IJV expansion and fluid flow behavior in astronauts have surfaced following thromboembolism reports. Our study explored regional volume distension and blood flow complexity in the IJV during progressive volume shifting. We observed stepwise volume distension and increasing flow dispersion with head-down tilting across all regions. Flow dispersion may pose a risk of future thromboembolism during prolonged volume shifts.
摘要：
姿势调整期间的血容量变化导致颈内静脉（IJV）不规则扩张。在微重力中,扩张可能导致血流淤滞和血栓栓塞，尽管区域影响和相关风险仍未被探索。我们表征了渐进头向下倾斜（HDT）（0°，-6°,-15°,-30°）使用常规超声和矢量流成像。我们还评估了低压大腿袖口（40mmHg）作为-6°HDT期间的流体移位对策。总IJV体积从仰卧(4.6±2.7mL)至-30°HDT(10.3±5.0mL)膨胀139±95%。头颅IJV区的血流分布具有更大的矢量均匀性（P<0.01），并且随着倾斜的增加而变得更加分散（P<0.01）。定性,在整个IJV的早期流动周期阶段，流动更加均匀，在流动后期更加混乱。这种杂乱无章的流动在靠近血管壁的地方加剧，靠近尾区，在更大的HDT期间。-6°HDT期间的低压大腿袖带减少了颅区的IJV体积（-12±15％；P<0.01），但不减少尾区（P=0.20），尽管流动均匀性没有变化(这两个区域，P>0.25）。我们描述了一种可扩展的IJV，可容纳沿其长度的大体积变化。主要在尾部区域发现了明显的流动分散，提示多方向的血流.大腿袖口似乎可有效降低IJV体积，但对流量复杂性的影响很小。沿血管长度的流量复杂性可能与慢性容量移位期间的IJV扩张有关，并且可能是流量停滞和未来血栓栓塞风险的诱因。
