Abstract：
What is the central question of this study? Facial skin blood flow (SBF) might increase during head-down tilt (HDT). However, the effect of HDT on facial SBF remains controversial. In addition, the changes in facial SBF in the cheek (cheek SBF) during a steeper angle of HDT (>-12° HDT) have not been investigated. What is the main finding and its importance? This study showed that cheek SBF decreased during -30° HDT, alongside increased vascular resistance. Furthermore, vascular impedance was suggested to be elevated, accompanied by an increased hydrostatic pressure gradient caused by HDT. Constriction of the facial skin vascular bed and congestion of venous return owing to the steep angle of HDT can decrease facial SBF.
Head-down tilt (HDT) has been used to simulate microgravity in ground-based studies and clinical procedures including the Trendelenburg position or in certain surgical operations. Facial skin blood flow (SBF) might be altered by HDT, but the effect of a steeper angle of HDT (>-12° HDT) on facial SBF remains unclear. We examined alterations in facial SBF in the cheek (cheek SBF) using two different angles (-10 and -30°) of HDT and lying horizontal (0°) in a supine position for 10 min, to test the hypothesis that cheek SBF would increase with a steeper angle of HDT. Cheek SBF was measured continuously by laser Doppler flowmetry. Cheek skin vascular resistance and the pulsatility index of cheek SBF were calculated to assess the circulatory effects on the facial skin vascular bed in the cheek. Cheek SBF decreased significantly during -30° HDT. In addition, the resistance in cheek SBF increased significantly during -30° HDT. The pulsatility index of cheek SBF increased during both -10 and -30° HDT. Contrary to our hypothesis, cheek SBF decreased during -30° HDT along with increased skin vascular resistance. Vascular impedance, estimated by the pulsatility index in the cheek SBF, was elevated during both -10 and -30° HDT, and elevated vascular impedance would be related to increased hydrostatic pressure induced by HDT. Skin vascular constriction and venous return congestion would be induced by -30° HDT, leading to deceased cheek SBF. The present study suggested that facial SBF in the cheek decreased during acute exposure to a steep angle of HDT (∼-30° HDT).
Head-down tilt (HDT) has been used to simulate microgravity in ground-based studies and clinical procedures including the Trendelenburg position or in certain surgical operations. Facial skin blood flow (SBF) might be altered by HDT, but the effect of a steeper angle of HDT (>-12° HDT) on facial SBF remains unclear. We examined alterations in facial SBF in the cheek (cheek SBF) using two different angles (-10 and -30°) of HDT and lying horizontal (0°) in a supine position for 10 min, to test the hypothesis that cheek SBF would increase with a steeper angle of HDT. Cheek SBF was measured continuously by laser Doppler flowmetry. Cheek skin vascular resistance and the pulsatility index of cheek SBF were calculated to assess the circulatory effects on the facial skin vascular bed in the cheek. Cheek SBF decreased significantly during -30° HDT. In addition, the resistance in cheek SBF increased significantly during -30° HDT. The pulsatility index of cheek SBF increased during both -10 and -30° HDT. Contrary to our hypothesis, cheek SBF decreased during -30° HDT along with increased skin vascular resistance. Vascular impedance, estimated by the pulsatility index in the cheek SBF, was elevated during both -10 and -30° HDT, and elevated vascular impedance would be related to increased hydrostatic pressure induced by HDT. Skin vascular constriction and venous return congestion would be induced by -30° HDT, leading to deceased cheek SBF. The present study suggested that facial SBF in the cheek decreased during acute exposure to a steep angle of HDT (∼-30° HDT).
摘要：
这项研究的中心问题是什么？头朝下倾斜（HDT）时，面部皮肤血流量（SBF）可能会增加。然而,HDT对面部SBF的影响仍存在争议。此外,在HDT更陡的角度(>-12°HDT)期间脸颊中面部SBF的变化(脸颊SBF)尚未被研究。主要发现及其重要性是什么？这项研究表明，脸颊SBF在-30°HDT期间下降，血管阻力增加。此外，建议血管阻抗升高，伴随着由HDT引起的静水压力梯度增加。由于HDT的陡峭角度，面部皮肤血管床的收缩和静脉回流的充血可以降低面部SBF。
头向下倾斜（HDT）已用于模拟地面研究和临床程序中的微重力，包括Trendelenburg位置或某些外科手术。HDT可能会改变面部皮肤血流量（SBF），但更陡的HDT角度（>-12°HDT）对面部SBF的影响尚不清楚。我们使用HDT的两个不同角度（-10和-30°）并以仰卧位水平（0°）放置10分钟，检查了脸颊（脸颊SBF）中面部SBF的变化，检验脸颊SBF会随着HDT的更陡角度而增加的假设。通过激光多普勒流量计连续测量脸颊SBF。计算脸颊皮肤血管阻力和脸颊SBF的搏动指数，以评估对脸颊面部皮肤血管床的循环作用。面颊SBF在-30°HDT期间显著降低。此外,在-30°HDT期间，脸颊SBF的阻力显着增加。在-10和-30°HDT期间，脸颊SBF的搏动指数均增加。与我们的假设相反,-30°HDT期间，脸颊SBF降低，皮肤血管阻力增加。血管阻抗,通过脸颊SBF的搏动指数估计，在-10和-30°HDT期间升高，血管阻抗升高与HDT引起的静水压力增加有关。-30°HDT会引起皮肤血管收缩和静脉回流充血，导致死者的脸颊SBF。本研究表明，在急性暴露于陡峭的HDT角度（〜-30°HDT）期间，脸颊中的面部SBF降低。
头向下倾斜（HDT）已用于模拟地面研究和临床程序中的微重力，包括Trendelenburg位置或某些外科手术。HDT可能会改变面部皮肤血流量（SBF），但更陡的HDT角度（>-12°HDT）对面部SBF的影响尚不清楚。我们使用HDT的两个不同角度（-10和-30°）并以仰卧位水平（0°）放置10分钟，检查了脸颊（脸颊SBF）中面部SBF的变化，检验脸颊SBF会随着HDT的更陡角度而增加的假设。通过激光多普勒流量计连续测量脸颊SBF。计算脸颊皮肤血管阻力和脸颊SBF的搏动指数，以评估对脸颊面部皮肤血管床的循环作用。面颊SBF在-30°HDT期间显著降低。此外,在-30°HDT期间，脸颊SBF的阻力显着增加。在-10和-30°HDT期间，脸颊SBF的搏动指数均增加。与我们的假设相反,-30°HDT期间，脸颊SBF降低，皮肤血管阻力增加。血管阻抗,通过脸颊SBF的搏动指数估计，在-10和-30°HDT期间升高，血管阻抗升高与HDT引起的静水压力增加有关。-30°HDT会引起皮肤血管收缩和静脉回流充血，导致死者的脸颊SBF。本研究表明，在急性暴露于陡峭的HDT角度（〜-30°HDT）期间，脸颊中的面部SBF降低。
