Design and evaluation of a flow phantom.

RATIONALE AND OBJECTIVES: We constructed a near-anatomically correct large-vessel phantom to perform repeatable flow dynamics research examinations by angiography, magnetic resonance (MR) angiography, and computed tomography (CT) angiography. METHODS: An internal carotid artery was constructed within a head phantom. The internal carotid artery branches into a middle and an anterior cerebral artery; the former trifurcates and ends in the superior sagittal sinus, and the latter ends in the inferior sagittal sinus. A transverse and sigmoid sinus drains the model. All four vessels connecting the arterial and venous vessels have variable flow-constricting ligatures placed around them. These ligatures are accessible on the skull surface. The skull cavity is filled with a silicone polymer that is isodense to brain on CT scans and isointense on most MR images. RESULTS: The flow in the phantom's vessels may be varied in a repeatable manner. Multiple scan sequences may be performed without the image degradation caused by patient motion. The homogeneity of the filler polymer allows visualization of flow-related artifacts that may be hidden by complex human anatomy. CONCLUSION: Preliminary images of each modality show promise for use of the phantom in imaging research on large-vessel flow dynamics.

Inotropic responses to cyclic nucleotide phosphodiesterase inhibitors in immature and adult rabbit myocardium.

Contractile dose-response relationships for amrinone, milrinone, piroximone, and sulmazole were compared in right ventricular papillary muscles isolated from adult and 14-16-day-old immature rabbits. These drugs were effective inotropic agents in immature myocardium as evidenced by substantial increases in the maximal rate of tension development. The rank order of maximum inotropic effect in the immature muscles was milrinone = sulmazole greater than piroximone greater than amrinone. Compared with adults, the relative magnitude of the inotropic response for each drug was greater in immature myocardium. Profiles of ventricular cytosolic cyclic nucleotide phosphodiesterase (PDE) activities resolved by anion exchange chromatography were similar for the two age groups. Immature myocardium was found to contain the Type IV (Peak III) high-affinity cAMP PDE that has been implicated in the mechanism of action of these drugs. Partially purified cytosolic Type IV PDE from immature and adult myocardium exhibited similar kinetic characteristics (cAMP Km = 0.9 microM; Vmax = 17 nmol/min/mg) and sensitivity to inhibition by cGMP. Except for piroximone, the inhibitory effect of each drug on cytosolic Type IV PDE activity from immature myocardium did not differ from the adult, as indexed by comparable concentrations required to inhibit activity by 50% (IC50) and Ki values (piroximone IC50 and Ki values were higher in the immature compared with the adult group). Thus, these studies demonstrated significant age-related differences in the contractile responses to amrinone, milrinone, piroximone, and sulmazole. These differences are not attributable to differences in myocardial cytosolic Type IV high-affinity cAMP PDE activity.(ABSTRACT TRUNCATED AT 250 WORDS)