Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, British Columbia, Canada.
J Appl Physiol (1985). 2020 Dec 1;129(6):1341-1347. doi: 10.1152/japplphysiol.00488.2020. Epub 2020 Oct 15.
The utility of transthoracic saline contrast echocardiography (TTSCE) to assess blood flow through intrapulmonary arteriovenous anastomoses (Q̇) in humans is limited due to the potential destabilizing effects of the gas concentration gradients established in varied blood-gas environments. This study assessed the specific effect of a hyperoxic and mixed venous blood-gas environment on the stability of saline contrast. We hypothesized that the rate of contrast mass lost in hyperoxic blood would be similar to mixed venous due to the establishment of equal and opposing gas gradients (O, N, CO) created when the partial pressure of dissolved gases is manipulated. Using an in vitro model of the pulmonary circulation perfused with defibrinated sheep blood and a membrane oxygenator to control blood gases, we assessed the percent contrast conserved (an index of contrast stability) between inflow and outflow sites at multiple flow rates (1.8, 2.8, 4.3, and 6.8 L/min) in a hyperoxic (Po: 646 ± 16 mmHg; Pco: 0 ± 0 mmHg) and a mixed venous blood gas condition (Po: 35 ± 3 mmHg; Pco: 40 ± 0 mmHg). We found significant contrast decay with time in both conditions, with slightly higher contrast conservation in the hyperoxia trials (64 ± 32%) versus the mixed venous trials (55 ± 21%). These findings suggest that contrast stability is not likely a factor affecting the interpretation of TTSCE performed in healthy humans breathing hyperoxia and lends support to the existence of a local O-dependent mechanism contributing to the regulation of Q̇. Hyperoxic blood has a small stabilizing effect on agitated saline contrast compared with mixed venous blood, lending support to studies that show the reversal of exercise-induced blood flow through intrapulmonary arteriovenous anastomoses (Q̇) with hyperoxia. These data support the possible presence of a local O-dependent regulatory mechanism within the pulmonary vasculature that may play a role in Q̇ regulation.
经胸盐水对比超声心动图（TTSCE）评估人体肺内动静脉吻合支（Q̇）血流的实用性有限，这是因为在不同的血气环境中建立的气体浓度梯度可能会导致不稳定。本研究评估了高氧和混合静脉血气环境对盐水对比稳定性的具体影响。我们假设，由于溶解气体分压的调节会产生相等且相反的气体梯度（O、N、CO），因此高氧血中对比剂质量的损失率与混合静脉血相似。我们使用用纤维蛋白原分解的绵羊血灌注的体外肺循环模型和膜式氧合器来控制血液气体，在多个流量（1.8、2.8、4.3 和 6.8 L/min）下评估了在高氧（Po：646 ± 16 mmHg；Pco：0 ± 0 mmHg）和混合静脉血气条件（Po：35 ± 3 mmHg；Pco：40 ± 0 mmHg）下，流入和流出部位之间的对比保留率（对比稳定性的指标）。我们发现两种条件下对比剂均随时间发生显著衰减，高氧试验中对比剂保留率略高（64 ± 32%），混合静脉试验中保留率略低（55 ± 21%）。这些发现表明，对比稳定性不太可能是影响在健康人群中进行的 TTSCE 解读的因素，并支持存在局部 O 依赖性机制来调节 Q̇的假设。与混合静脉血相比，高氧血对搅拌盐水对比剂具有较小的稳定作用，这支持了一些研究的结果，这些研究表明，高氧可逆转运动引起的肺内动静脉吻合支（Q̇）的血流。这些数据支持在肺血管中可能存在局部 O 依赖性调节机制，该机制可能在 Q̇调节中发挥作用。
