Load-sharing characteristics of stenting and post-dilation in heavily calcified coronary artery.

In this work, stenting in non-calcified and heavily calcified coronary arteries was quantified in terms of diameter-pressure relationships and load transfer from the balloon to the artery. The efficacy of post-dilation in non-calcified and heavily calcified coronary arteries was also characterized in terms of load sharing and the changes in tissue mechanics. Our results have shown that stent expansion exhibits a cylindrical shape in non-calcified lesions, while it exhibits a dog bone shape in heavily calcified lesions. Load-sharing analysis has shown that only a small portion of the pressure load (1.4 N, 0.8% of total pressure load) was transferred to the non-calcified lesion, while a large amount of the pressure load (19 N, 12%) was transferred to the heavily calcified lesion. In addition, the increasing inflation pressure (from 10 to 20 atm) can effectively increase the minimal lumen diameter (from 1.48 to 2.82 mm) of the heavily calcified lesion, the stress (from 1.5 to 8.4 MPa) and the strain energy in the calcification (1.77 mJ to 26.5 mJ), which are associated with the potential of calcification fracture. Results indicated that increasing inflation pressure can be an effective way to improve the stent expansion if a dog bone shape of the stenting profile is observed. Considering the risk of a balloon burst, our results support the design and application of the high-pressure balloon for post-dilation. This work also sheds some light on the stent design and choice of stent materials for improving the stent expansion at the dog bone region and mitigating stresses on arterial tissues.

The role of intrapartum fetal head compression in neonatal retinal hemorrhage.

PURPOSE: Neonatal retinal hemorrhage is a common finding in newborns, but the underlying mechanisms are not fully understood. A computational simulation was designed to study the events taking place in the eye and orbit when the head is compressed as the neonate passes through the birth canal. METHODS: A finite element model of the eye, optic nerve sheath, and orbit was simulated and subjected to forces mimicking rises in intracranial pressure (ICP) associated with maternal contractions during normal vaginal delivery. Resulting changes in intraocular pressure (IOP), pressure in the optic nerve sheath, and stress within the sclera and retina were measured. RESULTS: During contractions, increased ICP was transmitted to the orbit, globe, and optic nerve sheath. IOP rose by 2.71 kPa near the posterior pole. Pressure at the center of the optic nerve sheath rose by 7.31 kPa and up to 9.30 kPa at its interface with the sclera. Stress in the retina was highest near the optic disk and reached 10.93, 10.99, and 13.28 kPa in the preretinal, intraretinal, and subretinal layers, respectively. Stress in the sclera peaked at 12.76 kPa. CONCLUSIONS: Increasing ICP associated with natural vaginal delivery increases intraorbital pressure, which applies stress to the retina. Associated retinal deformation may cause tearing of the retinal vasculature. Increased pressure within the optic nerve sheath may occlude the central retinal vein, resulting in outflow obstruction and subsequent rupture. Forces accumulated near the optic disk, likely accounting for the tendency of neonatal retinal hemorrhage to occur posteriorly.

Load-sharing characteristics of stenting and post-dilation in heavily calcified coronary artery.

In this work, stenting in non-calcified and heavily calcified coronary arteries was quantified in terms of diameter-pressure relationships and load transfer from the balloon to the artery. The efficacy of post-dilation in non-calcified and heavily calcified coronary arteries was also characterized in terms of load sharing and the changes in tissue mechanics. Our results have shown that stent expansion exhibits a cylindrical shape in non-calcified lesions, while it exhibits a dog bone shape in heavily calcified lesions. Load-sharing analysis has shown that only a small portion of the pressure load (1.4 N, 0.8% of total pressure load) was transferred to the non-calcified lesion, while a large amount of the pressure load (19 N, 12%) was transferred to the heavily calcified lesion. In addition, the increasing inflation pressure (from 10 to 20 atm) can effectively increase the minimal lumen diameter (from 1.48 mm to 2.82 mm) of the heavily calcified lesion, the stress (from 1.5 MPa to 8.4 MPa) the strain energy in the calcification (1.77 mJ to 26.5 mJ), which associated with the potential of calcification fracture. Results indicated that increasing inflation pressure can be an effective way to improve the stent expansion if a dog bone shape of the stenting profile is observed. Considering the risk of a balloon burst, our results support the design and application of the high-pressure balloon for post-dilation.