Prasad P V, Edelman R R, Epstein F H
Department of Radiology and Medicine, Beth Israel Hospital, Boston, MA 02215, USA.
Circulation. 1996 Dec 15;94(12):3271-5. doi: 10.1161/01.cir.94.12.3271.
The countercurrent arrangement of capillary blood flow in the medulla of mammalian kidneys generates a gradient of oxygen tension between the renal cortex and the papillary tip that results in a state of relative hypoxia within the renal medulla. Exploration of the pathophysiological implications of medullary hypoxia has been hampered by the absence of a noninvasive technique to estimate intrarenal oxygenation in different zones of the kidney. In the present study, we demonstrate the feasibility of such a method on the basis of blood oxygenation level-dependent (BOLD) MRI, which allows sequential measurements in humans in response to a variety of physiological/ pharmacological stimuli in health and disease.
BOLD MRI measurements were obtained in healthy young human subjects (n = 7), and the effects of three different pharmacological/physiological maneuvers that induce diuresis were studied. Spin-spin relaxation rate, R2*, was measured, which is directly related to the amount of deoxyhemoglobin in blood and in turn to tissue PO2. Furosemide but not acetazolamide (n = 6 each) increased medullary oxygenation (delta R2* = 7.62 Hz; P < .01), consistent with the separate sites of action of these diuretics in the nephron and with previous direct measurements of their effects in anesthetized rats with oxygen microelectrodes. A new finding is that water diuresis improves medullary oxygenation (delta R2* = 6.43 Hz; P < .01) in young human subjects (n = 5).
BOLD MRI can be used to monitor changes in intrarenal oxygenation in humans in a noninvasive fashion.
哺乳动物肾脏髓质中毛细血管血流的逆流排列在肾皮质和乳头尖端之间产生了氧张力梯度，导致肾髓质处于相对缺氧状态。由于缺乏一种非侵入性技术来估计肾脏不同区域的肾内氧合情况，对髓质缺氧的病理生理意义的探索受到了阻碍。在本研究中，我们基于血氧水平依赖（BOLD）磁共振成像（MRI）证明了这种方法的可行性，该技术能够在健康和疾病状态下，根据各种生理/药理刺激对人体进行连续测量。
对健康年轻人体受试者（n = 7）进行了BOLD MRI测量，并研究了三种不同诱导利尿的药理/生理操作的效果。测量了自旋 - 自旋弛豫率R2*，它与血液中脱氧血红蛋白的量直接相关，进而与组织氧分压相关。呋塞米而非乙酰唑胺（每组n = 6）增加了髓质氧合（ΔR2* = 7.62 Hz；P <.01），这与这些利尿剂在肾单位中的不同作用位点以及先前在麻醉大鼠中使用氧微电极对其效果的直接测量结果一致。一个新发现是，水利尿可改善年轻人体受试者（n = 5）的髓质氧合（ΔR2* = 6.43 Hz；P <.01）。
BOLD MRI可用于以非侵入性方式监测人体肾内氧合的变化。
