The utility of transthoracic saline contrast echocardiography (TTSCE) to assess blood flow through intrapulmonary arteriovenous anastomoses (Q̇_IPAVA) 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 (O₂, N₂, CO₂) created when the partial pressure of dissolved gases are 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, 6.8 l/min) in a hyperoxic (PO₂: 646 ± 16 mmHg; PCO₂: 0 ± 0 mmHg) and a mixed venous blood gas condition (PO₂: 35 ± 3 mmHg; PCO₂: 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 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 O₂-dependent mechanism contributing to the regulation of Q̇_IPAVA.

中文翻译：

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血液PO ₂对搅动盐水对比稳定性的影响

由于在不同的血气环境中建立的气体浓度梯度可能产生不稳定作用，因此经胸盐水对比超声心动图（TTSCE）评估人类通过肺内动静脉吻合术（Q̇IPAVA ）的血流的_实用性受到限制。这项研究评估了高氧和混合静脉血气环境对盐水造影剂稳定性的特定影响。我们假设由于建立了相等且相对的气体梯度（O ₂，N ₂，CO _2），高氧血液中造影剂的流失率与混合静脉相似。）当溶解气体的分压被操纵时产生。我们使用体外纤维化的体外循环模型灌注了去纤维蛋白羊血和膜氧合器来控制血液中的气体，我们评估了多种流速（1.8、2.8，在高氧（PO ₂：646±16 mmHg; PCO ₂：0±0 mmHg）和混合静脉血气条件下（PO ₂：35±3 mmHg; PCO ₂）为4.3，6.8 l / min）：40±0 mmHg）。我们发现，在两种情况下，高氧试验（64±32％）的对比度保持率均显着下降，而混合静脉试验（55±21％）的对比度保持率稍高。这些发现表明，对比度稳定性不太可能是影响健康人呼吸性高氧反应中对TTSCE的解释的因素，并支持存在局部O ₂依赖性机制，从而有助于Q̇IPAVA的_调节。