Ayappa I, Brown L V, Lai-Fook S J
Center for Biomedical Engineering, Wenner-Gren Research Laboratory, University of Kentucky, Lexington 40506-0070, USA.
Respir Physiol. 1998 May;112(2):155-66. doi: 10.1016/s0034-5687(98)00022-x.
In previous studies using isolated perfused rabbit lungs, an O2 deficit measured by an alveolar gas-to-end capillary blood P(O2) difference (A-aD(O2)) was absent at blood flows (Q) consistent with severe exercise. Thus factors such as VA/Q heterogeneity, shunt and diffusion limitation that contribute to an O2 deficit in vivo were absent. Here we attempted to increase diffusion limitation to O2 transport by reducing the equilibration coefficient D/(betaQ), the ratio of the diffusing capacity (D) to the product of Q and the capacitance coefficient (beta, the slope of the blood O2 content-P(O2) curve). First, we used hypoxic (10% O2) ventilation in conjunction with a low PV(O2) (approximately 25 mmHg) because beta is largest in this region of the O2 dissociation curve. Second, we increased beta by decreasing blood P(CO2) which shifts the O2 dissociation curve to the left (Bohr effect). Third, we increased Q to three times control to reduce D/Q. CO diffusing capacity was measured as a function of blood flow and blood P(O2). A deficit in O2 transport as measured by a significant A-aD(O2) was measured only under conditions of hypoxia and high blood flow. The measured O2 deficit matched the predictions from the equilibration coefficients D/(betaQ) based on measurements of beta, D and Q.
在以往使用离体灌流兔肺的研究中，在与剧烈运动相符的血流量（Q）下，通过肺泡气与终末毛细血管血的氧分压差值（A-aD（O2））测得的氧亏并不存在。因此，体内导致氧亏的诸如通气/血流比值不均一性、分流和弥散限制等因素并不存在。在此，我们试图通过降低平衡系数D/（βQ）来增加氧转运的弥散限制，D/（βQ）即弥散能力（D）与Q和容量系数（β，血中氧含量-氧分压曲线的斜率）乘积的比值。首先，我们将低氧（10%氧气）通气与低肺动脉血氧分压（约25 mmHg）相结合，因为β在氧解离曲线的这一区域最大。其次，我们通过降低血二氧化碳分压来增加β，这会使氧解离曲线左移（波尔效应）。第三，我们将Q增加至对照的三倍以降低D/Q。测量了一氧化碳弥散能力随血流量和血氧分压的变化。仅在低氧和高血流量条件下，通过显著的A-aD（O2）测得存在氧转运亏缺。测得的氧亏与基于β、D和Q测量值的平衡系数D/（βQ）的预测结果相符。
