Experimental model for comparative evaluation of pharmacologically induced vasodilation of arterial wall mechanical properties.

Arterial wall compliance (C) and distensibility coefficient (DC) are key factors of pathologic physiology, especially in arteries less than 2 mm in diameter. The aim of this study was to design an experimental model allowing comparative measurement of C and DC during pharmacologically induced vasodilation on small-diameter arteries. Both femoral arteries were exposed in eight New Zealand White rabbits. Diameter (d) and systolic/diastolic diameter changes (deltad) were measured simultaneously, and C and DC were calculated before and after topical application of 1 mL of 4% papaverine on the right side and topical application of 1 mL of 1% lidocaine on the left side. Diameter measurements were performed by echo tracking with 20-MHz implanted microprobes. After papaverine and lidocaine application, respectively, d increased from 1.36 mm to 2.23 mm (P < 0.0001) and from 1.45 mm to 2.4 mm (P < 0.0001), deltad increased from 0.0568 mm to 0.0571 mm (P = 0.34) and from 0.064 mm to 0.077 mm (P < 0.01), C increased from 5.7 x 10(-3) mm/mm Hg to 6 x 10(-3) mm/mm Hg (P < 0.02) and from 6.23 x 10(-3) mm/mm Hg to 8.49 x 10(-3) mm/mm Hg (P < 0.01), and DC decreased from 4.22 x 10(-3) mm Hg(-1) to 2.61 x 10(-3) mm Hg(-1) (P < 0.0004) and from 4.36 x 10(-3) mm/mm Hg to 3.46 x 10(-3) mm/mm Hg (P < 0.005). Papaverine- and lidocaine-induced changes were significantly different for deltad, C, and DC (P < 0.01). These results suggest that, unlike that with papaverine, lidocaine-induced vasodilation leads the artery up to the nonlinear part of its pressure/diameter relationship, with decreased distensibility contrasting with increased diameter and compliance. Our experimental model may be useful to compare the effects of different vasoactive drugs at different concentrations on the mechanical properties of the arterial wall.

Wall mechanics of the stented rabbit aorta: long-term study and correlation with histological findings.

PURPOSE: To evaluate long-term changes in arterial wall mechanics induced by stenting of the rabbit aorta. METHODS: Eighteen New Zealand white rabbits had initial stent deployment (3x8 mm Multilink) at 110% of the pre-stenting abdominal aortic diameter. Group A (n=10) had no postdeployment stent expansion and group B (n=8) had 30% overdilation of the stent. A noninvasive B-mode ultrasound examination coupled with image processing allowed measurement of diameters at systole and diastole and the calculation of diameter compliance. Measurements were performed before stenting and compared to those recorded immediately after stenting and at 3 months at 3 locations: upstream from the stent, at the stent level, and downstream from the stent. Measurements were also compared among measurement sites. The pathological study included measurement of intimal thickening and calculation of an injury score. RESULTS: At the stent level, diameter compliance was significantly lower after initial stenting and at 3 months than before stenting (group A: p<0.005; group B: p<0.001) and than downstream or upstream from the stent (group A: p<0.0001, group B: p<0.005). No significant difference in diameter compliance was found between groups A and B. In group B, intimal thickening and the injury score were greater than in group A (p<0.05 and p<0.0001, respectively). CONCLUSIONS: Endovascular stenting of the rabbit aorta impairs wall mechanics. Performing 30% overdilation of the stent does not worsen this impairment but induces greater in-stent intimal hyperplasia.

Regional blood flows are affected differently by PEEP when the abdomen is open or closed: an experimental rabbit model.

OBJECTIVE: The study of induced circulatory changes requires simultaneous assessment of multiple regional circulations because of interactions and compensatory mechanisms. Positive end expiratory pressure mechanical ventilation (PEEP) is known to cause marked, and potentially deleterious, cardiovascular changes. Our aim was to use a comprehensive approach to assess PEEP-induced circulatory changes in open vs closed abdomen animals. MATERIAL AND METHODS: In the anesthetized rabbit, we used implantable Doppler micro-probes to measure blood flow simultaneously in the ascending aorta, inferior vena cava, portal vein, hepatic artery, common carotid artery, and renal artery. We studied spontaneously breathing animals (Group A), and open (Group B) and closed abdomen (Group C) animals mechanically ventilated at 0 (ZEEP) and 12 cm H(2)O PEEP. RESULTS: In Group A, all biological and hemodynamic variables remained unchanged for three hours at the end of the surgical procedure. In Groups B and C, ZEEP produced no significant hemodynamic change. PEEP induced a decrease in carotid, hepatic, and renal artery blood flow in Groups B and C, a decrease in heart rate and mean arterial blood pressure in Group B, and a decrease in aorta blood flow in Group C. CONCLUSIONS: These experimental results demonstrate the usefulness of the comprehensive approach of circulatory changes, and confirm that PEEP may have deleterious effects on regional blood flow, even without significant change in cardiac output, especially when the abdomen is open.

Arterial stenting and overdilation: does it change wall mechanics in small-caliber arteries?

PURPOSE: To evaluate changes in arterial wall mechanics induced by stent overdilation in the rabbit aorta. METHODS: Twenty New Zealand white rabbits had initial stent deployment (3-mm x 8-mm Multilink) at 10% overdilation. Group A (n=11) had no subsequent balloon expansion of the stent and Group B (n=9) had 30% overdilation of the stent. A noninvasive B-mode ultrasound examination coupled with image processing allowed the measurement of systolic and diastolic diameter and the calculation of diameter compliance (Cd) and distensibility coefficient (DC) as indexes of arterial wall biomechanics. Measurements were performed before stenting in the infrarenal aorta, after initial stenting, and after stent overdilation at 3 locations: upstream, at the stent level, and downstream from the stent. RESULTS: Cd was significantly lower in the stented aorta after initial stenting (p<0.0001) and after stent overdilation (p<0.0001) than before stenting. At the stent level, Cd and DC were significantly lower than downstream (p<0.0001) or upstream (p<0.0001) from the stent after initial stenting, as well as after stent overdilation. Downstream from the stent, Cd and DC were significantly lower after stent overdilation than before stenting (p<0.05). CONCLUSIONS: Endovascular stenting of the rabbit aorta produces a significant decrease in arterial wall compliance and distensibility. Stent overdilation is responsible for a slight additional decrease of compliance downstream from the stent.