Stochastic and exponential analysis of precordial washout curves for myocardial blood flow measurement. Experimental evaluation

Myocardial washout of sonicated iopamidol reflects coronary blood flow in the absence of autoregulation

OBJECTIVES

The aim of the study was to evaluate the relation between measurements derived from myocardial contrast echocardiography and coronary blood flow.

BACKGROUND

Contrast echocardiography has the potential for measuring blood flow.

METHODS

In six open chest anesthetized dogs, the left circumflex coronary artery was cannulated and perfused with blood drawn from the left femoral artery. While adenosine was infused into the circuit, circumflex flow was generated by a calibrated roller pump to the point of abolishing coronary autoregulation. At each of 25 levels of coronary blood flow, paired bolus injections of sonicated iopamidol were performed proximal to a mixing chamber. The perfused area of the left circumflex coronary artery was labeled by radioactive microspheres injected into the perfusion line. Two-dimensional echocardiographic images of the left ventricular short axis were digitized off-line, and myocardial videodensity was measured in the area perfused by the left circumflex coronary artery to generate time-intensity curves.

RESULTS

The washout slope of curves showed a good correlation with coronary blood flow, ranging from 0.5 to 12.5 ml/min per g of tissue. This correlation was good both in individual dogs (correlation coefficient [r] ranging from 0.78 to 0.96) and in the group of animals as a whole (r = 0.85). Washout slope also showed a good correlation with coronary diastolic pressure (r = 0.80), which ranged from 23 to 114 mm Hg, suggesting a possible primary effect of pressure on contrast washout. However, coronary blood flow appeared to be a stronger predictor of washout slope (partial F = 26.5, p < 0.001) than did perfusion pressure (partial F = 5.9, p < 0.05 by multiple regression). The injection to injection variability in myocardial washout slope appeared to be high (24%). The gamma variate fitting of curves did not improve the correlation with coronary flow (r = 0.78).

CONCLUSIONS

Myocardial washout of sonicated iopamidol reflects coronary blood flow in a model in which coronary autoregulation is abolished.

Selective drug-induced reduction of blood flow in tumor transplants

The effect of a calcium antagonist and a physiologic amine on tumor and muscle perfusion was investigated with the aim of improving the preconditions for external hyperthermia treatment of cancer. Nisoldipine (0.04-4.0 mg/kg) and 5-hydroxy tryptamine (5-HT) (0.2-8.0 mg/kg) were administered i.p. in Sprague-Dawley rats bearing Walker 256 carcinoma, Yoshida sarcoma, or a homologous tumor transplant derived from a spontaneous leiomyosarcoma of the uterus. At the maximum dosage used, nisoldipine injection caused a decrease of the regional washout rate of Xenon-133 of 63 +/- 8% (SEM) in the Walker carcinoma and an increase of 80 +/- 41% in the muscle of the hind leg. 5-HT (8 mg/kg) caused a drop of 79 +/- 29% in the Walker carcinoma and only a slight fall of the washout rate in muscle of 14 +/- 4.8%. Tumor-to-muscle uptake ratios of 11C-butanol fell from 5.63 +/- 1.98 to 3.32 +/- 1.21, and from 5.3 +/- 0.56 to 2.98 +/- 0.30, after injection of 0.2 mg/kg nisoldipine and 4 mg/kg 5-HT, respectively. Similar reaction patterns and percentage changes were observed in different tumor lines at constant doses of 0.2 mg/kg nisoldipine and 4 mg/kg 5-HT. Both drugs representing two different rationales of vasomotor action were able to reduce blood flow specifically in transplanted tumors; nisoldipine increased muscle blood flow and decreased arterial blood pressure, whereas 5-HT acted without substantial systemic effects.