Costelle Anna, Lu Junlan, Leewiwatwong Suphachart, Westerhof Berend, Mummy David, Rajagopal Sudarshan, Driehuys Bastiaan
Medical Physics Graduate Program, Duke University, Durham, North Carolina, United States.
Biomedical Engineering Graduate Program, Duke University, Durham, North Carolina, United States.
J Appl Physiol (1985). 2025 Mar 1;138(3):623-633. doi: 10.1152/japplphysiol.00440.2024. Epub 2025 Jan 28.
Hyperpolarized Xe MRI/MRS enables quantitative mapping of function in lung airspaces, membrane tissue, and red blood cells (RBCs) within the pulmonary capillaries. The RBC signal also exhibits cardiogenic oscillations that are reduced in precapillary pulmonary hypertension (PH). This effect is obscured in patients with concomitant defects in transfer from airspaces to RBCs, which increase RBC oscillation amplitudes. Here, we provide a framework for interpreting RBC oscillations and show their relationship to pulsatile blood flow, capillary blood volume, capillary compliance, and impedance of the capillary and venous circulation. This framework was first applied to characterize RBC oscillations in a cohort of subjects with pulmonary disease but no known PH ( = 129). Xe MRI of RBC transfer was used to estimate capillary blood volume, and as it decreased, RBC oscillations sharply increased ([Formula: see text] = 0.53), consistent with model predictions. Model-derived fit parameters were then used to estimate the distribution of pulmonary vascular resistance (PVR) across arterial, capillary, and venous circulation and to correct oscillations for RBC transfer defects. Seventy percent of PVR was estimated to arise from pulmonary arteries, 11% from capillaries, and 19% from veins. When tested in a second cohort of subjects who underwent Xe MRI/MRS and right heart catheterization ( = 40), oscillations corrected for capillary blood volume correlated moderately with PVR ( = 0.27, = 0.0014). For every 1.96 Wood units (WU) increase in PVR, corrected oscillations decreased by 1 absolute percentage point. This work demonstrates that, although Xe-RBC oscillations are only indirectly sensitive to precapillary obstruction, corrected oscillations below 7.5% were 100% specific for elevated PVR. Cardiogenic oscillations in the Xe red blood cell (RBC) resonance decrease in precapillary pulmonary hypertension (PH) but are enhanced when capillary blood volume is reduced. To separate these effects, we developed a physiological model that used Xe gas exchange MRI to estimate blood volume, which was used to correct oscillation amplitude measurements. Corrected amplitudes correlated significantly with pulmonary vascular resistance, highlighting the potential for future noninvasive detection of PH.
超极化氙气磁共振成像/磁共振波谱能够对肺内气腔、膜组织以及肺毛细血管内的红细胞（RBC）功能进行定量映射。红细胞信号还表现出心源性振荡，而在毛细血管前肺动脉高压（PH）中这种振荡会减弱。在气腔到红细胞转运存在伴随缺陷的患者中，这种效应会被掩盖，因为这些缺陷会增加红细胞振荡幅度。在此，我们提供了一个解释红细胞振荡的框架，并展示了它们与搏动性血流、毛细血管血容量、毛细血管顺应性以及毛细血管和静脉循环阻抗之间的关系。该框架首先应用于一组患有肺部疾病但无已知肺动脉高压（PH）的受试者（n = 129），以表征红细胞振荡。利用红细胞转运的氙气磁共振成像来估计毛细血管血容量，随着其降低，红细胞振荡急剧增加（R² = 0.53），这与模型预测一致。然后，使用模型推导的拟合参数来估计肺血管阻力（PVR）在动脉、毛细血管和静脉循环中的分布，并校正红细胞转运缺陷导致的振荡。估计70%的PVR源于肺动脉，11%源于毛细血管，19%源于静脉。在另一组接受氙气磁共振成像/磁共振波谱和右心导管检查的受试者（n = 40）中进行测试时，校正后的毛细血管血容量振荡与PVR呈中度相关（R = 0.27，P = 0.0014）。PVR每增加1.96伍德单位（WU），校正后的振荡就下降1个绝对百分点。这项工作表明，尽管氙气 - 红细胞振荡仅对毛细血管前阻塞间接敏感，但校正后低于7.5%的振荡对升高的PVR具有100%的特异性。在毛细血管前肺动脉高压（PH）中，氙气红细胞（RBC）共振中的心源性振荡会减弱，但当毛细血管血容量减少时会增强。为了区分这些效应，我们开发了一个生理模型，该模型使用氙气气体交换磁共振成像来估计血容量，用于校正振荡幅度测量。校正后的幅度与肺血管阻力显著相关，突出了未来无创检测肺动脉高压的潜力。
