Georgakopoulos D, Kass D A
Division of Cardiology, Department of Medicine and Department of Biomedical Engineering, The Johns Hopkins Medical Institutions, Baltimore, Maryland 21287, USA.
Am J Physiol Heart Circ Physiol. 2000 Jul;279(1):H443-50. doi: 10.1152/ajpheart.2000.279.1.H443.
The conductance catheter method has substantially enhanced the characterization of in vivo cardiovascular function in mice. Absolute volume determination requires assessment of parallel conductance (V(p)) offset because of conductivity of structures external to the blood pool. Although such a determination is achievable by hypertonic saline bolus injection, this method poses potential risks to mice because of volume loading and/or contractility changes. We tested another method based on differences between blood and muscle conductances at various catheter excitation frequencies (20 vs. 2 kHz) in 33 open-chest mice. The ratio of mean frequency-dependent signal difference to V(p) derived by hypertonic saline injection was consistent [0.095 +/- 0.01 (SD), n = 11], and both methods were strongly correlated (r(2) = 0.97, P < 0.0001). This correlation persisted when the ratio was prospectively applied to a separate group of animals (n = 12), with a combined regression relation of V(p(DF)) = 1.1 * V(p(Sal)) - 2.5 [where V(p(DF)) is V(p) derived by the dual-frequency method and V(p(Sal)) is V(p) derived by hypertonic saline bolus injection], r(2) = 0.95, standard error of the estimate = 1.1 microl, and mean difference = 0.6 +/- 1.4 microl. Varying V(p(Sal)) in a given animal resulted in parallel changes in V(p(DF)) (multiple regression r(2) = 0.92, P < 0.00001). The dominant source of V(p) in mice was found to be the left ventricular wall itself, since surrounding the heart in the chest with physiological saline or markedly varying right ventricular volumes had a minimal effect on the left ventricular volume signal. On the basis of V(p) and flow probe-derived cardiac output, end-diastolic volume and ejection fraction in normal mice were 28 +/- 3 microl and 81 +/- 6%, respectively, at a heart rate of 622 +/- 28 min(-1). Thus the dual-frequency method and independent flow signal can be used to provide absolute volumes in mice.
电导导管法极大地增强了对小鼠体内心血管功能的表征。绝对容积测定需要评估由于血池外部结构的导电性导致的平行电导（V(p)）偏移。尽管通过高渗盐水团注可以实现这种测定，但由于容量负荷和/或收缩性变化，该方法对小鼠存在潜在风险。我们在33只开胸小鼠中测试了另一种基于不同导管激发频率（20 kHz与2 kHz）下血液与肌肉电导差异的方法。通过高渗盐水注射得出的平均频率依赖性信号差异与V(p)的比值是一致的[0.095±0.01（标准差），n = 11]，并且两种方法高度相关（r(2)= 0.97，P < 0.0001）。当将该比值前瞻性地应用于另一组动物（n = 12）时，这种相关性仍然存在，V(p(DF)) = 1.1 * V(p(Sal)) - 2.5的联合回归关系成立[其中V(p(DF))是通过双频法得出的V(p)，V(p(Sal))是通过高渗盐水团注注射得出的V(p)]，r(2)= 0.95，估计标准误差 = 1.1微升，平均差异 = 0.6±1.4微升。在给定动物中改变V(p(Sal))会导致V(p(DF))平行变化（多元回归r(2)= 0.92，P < 0.00001）。发现小鼠中V(p)的主要来源是左心室壁本身，因为用生理盐水围绕胸部的心脏或显著改变右心室容积对左心室容积信号的影响最小。基于V(p)和流量探头得出的心输出量，正常小鼠在心率为622±28次/分钟时，舒张末期容积和射血分数分别为28±3微升和81±6%。因此，双频法和独立的流量信号可用于提供小鼠的绝对容积。
