Department of Biological Sciences, Northern Arizona University , Flagstaff, Arizona.
Department of Human Physiology, University of Oregon , Eugene, Oregon.
J Appl Physiol (1985). 2017 Dec 1;123(6):1592-1598. doi: 10.1152/japplphysiol.00673.2017. Epub 2017 Sep 28.
Blood flow through intrapulmonary arteriovenous anastomoses (Q̇) increases in healthy humans breathing hypoxic gas and is potentially dependent on body position. Previous work in subjects breathing room air has shown an effect of body position when Q̇ is detected with transthoracic saline contrast echocardiography (TTSCE). However, the potential effect of body position on Q̇ has not been investigated when subjects are breathing hypoxic gas or with a technique capable of quantifying Q̇. Thus the purpose of this study was to quantify the effect of body position on Q̇ when breathing normoxic and hypoxic gas at rest. We studied Q̇ with TTSCE and quantified Q̇ with filtered technetium-99m-labeled macroaggregates of albumin (Tc-MAA) in seven healthy men breathing normoxic and hypoxic (12% O) gas at rest while supine and upright. On the basis of previous work using TTSCE, we hypothesized that the quantified Q̇ would be greatest with hypoxia in the supine position. We found that Q̇ quantified with Tc-MAA significantly increased while subjects breathed hypoxic gas in both supine and upright body positions (ΔQ̇ = 0.7 ± 0.4 vs. 2.5 ± 1.1% of cardiac output, respectively). Q̇ detected with TTSCE increased from normoxia in supine hypoxia but not in upright hypoxia (median hypoxia bubble score of 2 vs. 0, respectively). Surprisingly, Q̇ magnitude was greatest in upright hypoxia, when Q̇ was undetectable with TTSCE. These findings suggest that the relationship between TTSCE and Tc-MAA is more complex than previously appreciated, perhaps because of the different physical properties of bubbles and MAA in solution. NEW & NOTEWORTHY Using saline contrast bubbles and radiolabeled macroaggregrates (MAA), we detected and quantified, respectively, hypoxia-induced blood flow through intrapulmonary arteriovenous anastomoses (Q̇) in supine and upright body positions in healthy men. Upright hypoxia resulted in the largest magnitude of Q̇ quantified with MAA but the lowest Q̇ detected with saline contrast bubbles. These surprising results suggest that the differences in physical properties between saline contrast bubbles and MAA in blood may affect their behavior in vivo.
肺内动静脉吻合（Q̇）的血流在健康人呼吸低氧气体时增加，并且可能依赖于体位。先前在呼吸室内空气的受试者中进行的工作表明，当使用经胸盐水对比超声心动图（TTSCE）检测 Q̇时，体位会产生影响。然而，当受试者呼吸低氧气体或使用能够量化 Q̇的技术时，尚未研究体位对 Q̇的潜在影响。因此，本研究的目的是在休息时量化健康男性在呼吸正常氧和低氧气体时体位对 Q̇的影响。我们使用 TTSCE 量化 Q̇，并用过滤的锝-99m 标记的白蛋白微球（Tc-MAA）定量 Q̇。在休息时，七名健康男性在仰卧和直立两种体位下分别呼吸正常氧和低氧（12% O）气体。基于先前使用 TTSCE 的工作，我们假设在仰卧位时，用 TTSCE 定量的 Q̇最大。我们发现，当受试者在仰卧和直立两种体位下呼吸低氧气体时，Tc-MAA 定量的 Q̇显著增加（ΔQ̇分别为 0.7±0.4 和 2.5±1.1%的心输出量）。在仰卧位低氧时，TTSCE 检测到的 Q̇从正常氧增加，但在直立位低氧时则没有（中位数低氧气泡评分分别为 2 和 0）。令人惊讶的是，在 TTSCE 无法检测到 Q̇时，直立位低氧时 Q̇最大。这些发现表明，TTSCE 和 Tc-MAA 之间的关系比以前想象的更为复杂，这可能是由于溶液中气泡和 MAA 的物理性质不同所致。新发现和值得注意的是，我们分别使用盐水对比气泡和放射性标记的微球（MAA），在健康男性的仰卧和直立体位下检测和量化了低氧诱导的肺内动静脉吻合（Q̇）血流。在直立位低氧时，用 MAA 量化的 Q̇幅度最大，但用盐水对比气泡检测到的 Q̇最低。这些令人惊讶的结果表明，盐水对比气泡和血液中的 MAA 在物理性质上的差异可能会影响它们在体内的行为。
