Kedem J, Lee W W, Weiss H R
Department of Physiology and Biophysics, UMDNJ-Robert Wood Johnson Medical School, Piscataway 08854-5635.
Ann Biomed Eng. 1994 Jan-Feb;22(1):58-65. doi: 10.1007/BF02368222.
We determined the capabilities and limitations of an experimental approach to measure segment work (force x distance) of myocardial regions in the in vivo beating heart. In 18 open-chest anesthetized dogs, segment length was measured using ultrasonic dimension transducers, and developed force was measured with miniature force transducers. Work was defined as the integrated multiples of instantaneous force and shortening during a single (averaged) beat, corresponding to the area under the length-force loop. Changes in work over a range of 9.78 x 10(-4) to 2.93 x 10(-2) J/g/min were produced by vena caval constriction, aortic constriction, atrial pacing, and isoproterenol (0.5 and 1.0 micrograms/kg/min). Work was measured in both major and minor axes. In 60% of the animals, work in the minor axis was 9.2-fold greater than in the major axis. In the others, all interventions changed regional work to the same extent in both axes (r = 0.802; p < 0.05). Work changes were also compared between the base, anterior, and posterior walls. The response was directionally similar in all regions, ranging from -79 +/- 1% during caval occlusion to 278 +/- 98% during isoproterenol. The effective size of the measured muscle mass was limited to the transducer area because the amplitude and pattern of both force development and segment shortening were not changed until deep myocardial cuts were as close as 2 mm from the measuring area. We conclude that work measurement in the minor axis is quantitatively representative of fiber work in that region.
我们确定了一种实验方法的能力和局限性，该方法用于测量活体跳动心脏中心肌区域的节段功（力×距离）。在18只开胸麻醉犬中，使用超声尺寸换能器测量节段长度，并用微型力换能器测量产生的力。功被定义为单个（平均）心动周期中瞬时力和缩短量的积分倍数，对应于长度-力环下的面积。通过腔静脉缩窄、主动脉缩窄、心房起搏和异丙肾上腺素（0.5和1.0微克/千克/分钟）产生了9.78×10⁻⁴至2.93×10⁻²焦耳/克/分钟范围内的功变化。在长轴和短轴上均测量了功。在60%的动物中，短轴上的功比长轴上的功大9.2倍。在其他动物中，所有干预措施在两个轴上对区域功的改变程度相同（r = 0.802；p < 0.05）。还比较了心底、前壁和后壁之间的功变化。所有区域的反应在方向上相似，从腔静脉闭塞时的-79±1%到异丙肾上腺素时的278±98%。所测量的肌肉质量的有效大小限于换能器区域，因为直到距测量区域2毫米处进行深层心肌切割，力的产生和节段缩短的幅度及模式才会改变。我们得出结论，短轴上的功测量在定量上代表了该区域纤维的功。
