Grubb N R, van Doorn C A, Sutherland G R, Fox K A, Hooper T L
Cardiovascular Research Unit, University of Edinburgh, United Kingdom.
J Card Surg. 1997 Nov-Dec;12(6):420-30. doi: 10.1111/j.1540-8191.1997.tb00163.x.
Skeletal muscle ventricles (SMVs) are a potential power source for circulatory assistance. Noninvasive assessment of SMVs is desirable in long-term studies of SMV function. This study evaluated whether tissue velocity imaging (TVI) indices of function correlate with invasive measurements of output and pressure generation and examined the potential of TVI to provide information about SMV geometry and wall contraction characteristics.
SMVs were constructed in six sheep. After electrical conditioning, SMVs were connected to a mock circulation and stimulated with supramaximal 30-Hz and 50-Hz bursts to contract 35 times/min. The SMVs were tested over a range of preloads, and afterload was adjusted to simulate systemic (80 mmHg) and right ventricular (30 mmHg) loading conditions. Stroke volume and pressure were measured invasively, and stroke work was calculated. TVI was used to measure velocities in two opposing SMV walls, providing a simple wall motion score (WMS). This was evaluated against stroke volume, stroke work, and pressure development.
50-Hz stimulation frequency and high preload optimized SMV performance. Optimal SMV performance indices (mean at 50 Hz) were as follows: (a) right ventricular loading conditions (preload 30 mmHg), stroke volume 17.6 mL (SEM 3.2), peak pressure over afterload 44.2 mmHg (10.9), stroke work 0.05 J (0.02); (b) systemic loading conditions (preload 60 mmHg), stroke volume 10.1 mL (3.2), peak pressure over afterload 58 mmHg (14.6), stroke work 0.08 J (0.03). With low preloads, geometric anomalies were noted in the SMVs using TVI. Collapse of the SMVs and dyskinesis were observed, which normalized with higher preloads. Persistent dyskinesis was noted in one SMV and was associated with poor performance. Correlations (at optimal loading and stimulation settings) were as follows: systemic loading conditions, stroke volume versus WMS, 0.92 (p = 0.026); peak pressure versus WMS 0.89 (p = 0.045); stroke work versus WMS, r = 0.91 (p = 0.046). Right ventricular loading conditions were as follows: stroke volume versus WMS, 0.63 (p = 0.25); peak pressure versus WMS, 0.66 (p = 0.22); stroke work versus WMS, 0.45 (p = 0.39).
Under systemic loading conditions, TVI indices of SMV wall motion mirror invasive indices of performance, suggesting that TVI may be a useful tool for long-term noninvasive monitoring of SMV function.
骨骼肌心室（SMV）是循环辅助的潜在动力源。在SMV功能的长期研究中，对其进行无创评估是很有必要的。本研究评估了组织速度成像（TVI）功能指标是否与输出量和压力产生的有创测量值相关，并研究了TVI提供有关SMV几何形状和壁收缩特征信息的潜力。
在六只绵羊身上构建了SMV。电调节后，将SMV连接到模拟循环，并以30Hz和50Hz的超强脉冲刺激，使其以每分钟35次的频率收缩。在一系列前负荷范围内对SMV进行测试，并调整后负荷以模拟全身（80mmHg）和右心室（30mmHg）的负荷条件。有创测量每搏输出量和压力，并计算每搏功。使用TVI测量两个相对SMV壁的速度，得出一个简单的壁运动评分（WMS）。根据每搏输出量、每搏功和压力变化对其进行评估。
50Hz的刺激频率和高前负荷可优化SMV性能。最佳SMV性能指标（50Hz时的平均值）如下：（a）右心室负荷条件（前负荷30mmHg），每搏输出量17.6mL（标准误3.2），后负荷峰值压力44.2mmHg（10.9），每搏功0.05J（0.02）；（b）全身负荷条件（前负荷60mmHg），每搏输出量10.1mL（3.2），后负荷峰值压力58mmHg（14.6），每搏功0.08J（0.03）。在前负荷较低时，使用TVI观察到SMV存在几何异常。观察到SMV塌陷和运动障碍，在前负荷较高时恢复正常。在一个SMV中观察到持续的运动障碍，且其性能较差。（在最佳负荷和刺激设置下）相关性如下：全身负荷条件下，每搏输出量与WMS的相关性为0.92（p = 0.026）；峰值压力与WMS的相关性为0.89（p = 0.045）；每搏功与WMS的相关性，r = 0.91（p = 0.046）。右心室负荷条件下：每搏输出量与WMS的相关性为0.63（p = 0.25）；峰值压力与WMS的相关性为0.66（p = 0.22）；每搏功与WMS的相关性为0.45（p = 0.39）。
在全身负荷条件下，SMV壁运动的TVI指标反映了有创性能指标，表明TVI可能是长期无创监测SMV功能的有用工具。
