Reyes Maricela, Steinhelper Mark E, Alvarez Jorge A, Escobedo Daniel, Pearce John, Valvano Jonathan W, Pollock Brad H, Wei Chia-Ling, Kottam Anil, Altman David, Bailey Steven, Thomsen Sharon, Lee Shuko, Colston James T, Oh Jung Hwan, Freeman Gregory L, Feldman Marc D
Univ. of Texas Health Science Center, 7703 Floyd Curl Dr., San Antonio, TX 78229-3900, USA.
Am J Physiol Heart Circ Physiol. 2006 Oct;291(4):H1659-69. doi: 10.1152/ajpheart.00609.2005. Epub 2006 May 12.
Conductance measurements for generation of an instantaneous left ventricular (LV) volume signal in the mouse are limited, because the volume signal is a combination of blood and LV muscle, and only the blood signal is desired. We have developed a conductance system that operates at two simultaneous frequencies to identify and remove the myocardial contribution to the instantaneous volume signal. This system is based on the observation that myocardial resistivity varies with frequency, whereas blood resistivity does not. For calculation of LV blood volume with the dual-frequency conductance system in mice, in vivo murine myocardial resistivity was measured and combined with an analytic approach. The goals of the present study were to identify and minimize the sources of error in the measurement of myocardial resistivity to enhance the accuracy of the dual-frequency conductance system. We extended these findings to a gene-altered mouse model to determine the impact of measured myocardial resistivity on the calculation of LV pressure-volume relations. We examined the impact of temperature, timing of the measurement during the cardiac cycle, breeding strain, anisotropy, and intrameasurement and interanimal variability on the measurement of intact murine myocardial resistivity. Applying this knowledge to diabetic and nondiabetic 11- and 20- to 24-wk-old mice, we demonstrated differences in myocardial resistivity at low frequencies, enhancement of LV systolic function at 11 wk and LV dilation at 20-24 wk, and histological and electron-microscopic studies demonstrating greater glycogen deposition in the diabetic mice. This study demonstrated the accurate technique of measuring myocardial resistivity and its impact on the determination of LV pressure-volume relations in gene-altered mice.
用于在小鼠中生成瞬时左心室（LV）容积信号的电导测量受到限制，因为容积信号是血液和左心室心肌的组合，而我们只需要血液信号。我们开发了一种在两个同时存在的频率下运行的电导系统，以识别并去除心肌对瞬时容积信号的贡献。该系统基于这样的观察结果：心肌电阻率随频率变化，而血液电阻率则不随频率变化。为了用双频电导系统计算小鼠的左心室血容量，我们测量了体内小鼠的心肌电阻率，并结合了一种分析方法。本研究的目的是识别并最小化心肌电阻率测量中的误差来源，以提高双频电导系统的准确性。我们将这些发现扩展到基因改变的小鼠模型，以确定测量的心肌电阻率对左心室压力-容积关系计算的影响。我们研究了温度、心动周期中测量的时间、繁殖品系、各向异性以及测量内和动物间变异性对完整小鼠心肌电阻率测量的影响。将这些知识应用于11周龄以及20至24周龄的糖尿病和非糖尿病小鼠，我们证明了低频下心肌电阻率的差异、11周龄时左心室收缩功能的增强以及20至24周龄时左心室扩张，并且组织学和电子显微镜研究表明糖尿病小鼠中糖原沉积更多。这项研究证明了测量心肌电阻率的准确技术及其对基因改变小鼠左心室压力-容积关系测定的影响。
