Centre for Human and Applied Physiological Sciences (CHAPS), Faculty of Life Sciences and Medicine, King's College London, London, UK.
Department of Respiratory Therapy, College of Applied Medical Sciences, Jazan University, Jazan, Saudi Arabia.
Exp Physiol. 2024 Dec;109(12):2134-2146. doi: 10.1113/EP092014. Epub 2024 Oct 24.
Postural fluid shifts may directly affect respiratory control via a complex interaction of baro- and chemo-reflexes, and cerebral blood flow. Few data exist concerning the steady state ventilatory responses during head-down tilt. We examined the cardiorespiratory responses during acute 50° head-down tilt (HDT) in 18 healthy subjects (mean [SD] age 27 [10] years). Protocol 1 (n = 8, two female) was 50° HDT from 60° head-up posture sustained for 10 min, while exposed to normoxia, normoxic hypercapnia (5% CO), hypoxia (12% inspired O) or hyperoxic hypercapnia (95% O, 5% CO). Protocol 2 (n = 10, four female) was 50° HDT from supine, sustained for 10 min, while breathing either medical air or normoxic hypercapnic (5% CO) gas. Ventilation ( , pneumotachograph), end-tidal O and CO concentration and blood pressure (Finapres) were measured continuously throughout each protocol. Middle cerebral artery blood flow velocity (MCAv; transcranial Doppler) was also measured during protocol 2. Ventilation increased significantly (P < 0.05) compared to baseline during HDT in both hyperoxic hypercapnia (protocol 1 by mean [SD] 139 [26]%) and normoxic hypercapnia (protocol 1 by mean [SD] 131 [21]% and protocol 2 by 129 [23]%), despite no change in or from baseline. No change in was observed during HDT with medical air or hypoxia, and there was no significant change in MCAv during HDT compared to baseline. The absence of change in cerebral blood flow leads us to postulate that the augmented ventilatory response during steep HDT may involve mechanisms related to cerebral venous pressure and venous outflow.
体位性液体转移可能通过压力和化学反射以及脑血流的复杂相互作用直接影响呼吸控制。关于头低位倾斜时稳定状态通气反应的数据很少。我们检查了 18 名健康受试者（平均[标准差]年龄 27 [10]岁）急性 50°头低位倾斜（HDT）期间的心肺反应。方案 1（n=8，2 名女性）为从 60°头高位持续 10 分钟至 50° HDT，同时暴露于常氧、常氧高碳酸血症（5% CO）、缺氧（12%吸入 O）或高氧高碳酸血症（95% O，5% CO）。方案 2（n=10，4 名女性）为从仰卧位至 50° HDT，持续 10 分钟，同时呼吸医用空气或常氧高碳酸血症（5% CO）气体。通气量（ ，测压计）、呼气末 O 和 CO 浓度和血压（Finapres）在每个方案期间连续测量。方案 2 期间还测量了大脑中动脉血流速度（MCAv；经颅多普勒）。与基线相比，在高氧高碳酸血症（方案 1 平均增加[标准差]139[26]%）和常氧高碳酸血症（方案 1 平均增加[标准差]131[21]%和方案 2 增加 129[23]%）期间，HDT 时通气量显著增加（P<0.05），尽管 或 与基线相比没有变化。在医用空气或缺氧时 HDT 期间未观察到 变化，与基线相比，HDT 期间 MCAv 没有明显变化。由于脑血流没有变化，我们推测在陡峭 HDT 期间增强的通气反应可能涉及与脑静脉压和静脉流出相关的机制。
