Repeat microsphere delivery for serial measurement of regional blood perfusion in the chronically instrumented, conscious canine

Abstract

Introduction: For chronic, repeat hemodynamic studies in conscious dogs, we designed and tested a chronically instrumented canine microsphere delivery model. The goals of this study were (1) to investigate the accuracy of repeated estimations of blood perfusion using fluorescent-labeled microspheres and (2) to develop and validate a chronic preparation that permits consecutive estimations in the same conscious animal over an extended protocol.

Methods: Via thoracotomy, nine dogs were instrumented with left atrial appendage and aortic vascular access catheters connected to subcutaneous vascular access ports. Four animals received seven serial injections of 1.6 million 15 microm microspheres (total: 11.2 million), and five animals received 8 serial injections of 2.25 million microspheres (total: 18 million) over the course of 11 or 18 wk.

Results: All catheters have remained bidirectionally patent during protocol for 14.9 +/- 0.8 (mean +/- SEM) wk. Sphere accumulation did not significantly alter global myocardial (P = 0.69, P = 0.25), renal (P = 0.92, P = 0.12), hepatic (P = 0.84, P = 0.32), or splenic (P = 0.33, P = 0.70) blood perfusion in either set of animals.

Conclusions: Catheters remained bidirectionally patent for months, did not interfere with the hemodynamic responses of the preparation, and allowed repeat percutaneous injection of microspheres and withdrawal of reference arterial blood from within conscious canines. Eight serial injections totaling 18 million microspheres over 18 weeks did not alter regional myocardial, hepatic, renal, or splenic blood flow. This dependable, chronic, percutaneous arterial access preparation provides a means for examining acute and long-term effects of pathophysiological, pharmaceutical, and environmental influences on regional arterial blood flow in conscious, large animals.

Figure 1

A Catheter Securement to Left Atrial Appendage. A 7-Fr, radio-opaque silicon catheter was inserted 4-cm into the left atrial appendage. After implantation, the catheter is secured to the surface of the left atrial appendage. The two purse-string sutures are tied and secured to the first fastener loop. The second fastener loop is secured near the tip of the left atrial appendage. B Intra-Atrial View of Catheter Tip Fifteen Weeks Post-Implantation. There was no overgrowth of tissue around the intra-atrial segment of catheter. Minimum fibrous growth and chronic inflammation, no necrosis, and no infection were observed at the catheter entry site into the left atrial appendage. This depth and the angle of catheter entry parallel to the surface of the atrial appendage ensured that the catheter did not interfere with mitral valve function.

Figure 2

A Catheter Securement to Aorta. After implantation, the catheter is secured to the aortic wall. The two purse-string sutures are tied and secured to the first fastener loop. The second fastener loop is secured further up on the aorta. B: Intraluminal View of Intra-Aortic Catheter. There was no overgrowth of tissue around the intravascular segment of catheter. Minimum fibrous growth and chronic inflammation, no necrosis, and no infection were observed.

Figure 3

Individual Organ Perfusion ± SEM Before and After Multiple Injection of Polystyrene Microspheres A Hepatic, renal, splenic, and posterior left ventricle blood flow pre- and post- injection of 11.2 million microspheres. B Hepatic, renal, splenic, and posterior left ventricle blood flow pre- and post- injection of 18 million microspheres. C Combined results from Figure 3A and Figure 3B.