Computational analysis of the effectiveness of blood flushing with saline injection from an intravascular diagnostic catheter

In silico intravascular optical coherence tomography (IVOCT) for quality assured imaging with reduced intervention

In the clinical application of intravascular optical coherence tomography (IVOCT), it is necessary to flush opaque blood during image acquisition. However, there are no specific standards for how to perform low-dose but effective flushing. In this study, computational fluid dynamics (CFD) and optical models were integrated to numerically simulate the complete process of IVOCT, which includes blood flushing with normal saline followed by image acquisition. Moreover, an intermittent injection scheme was proposed, and its advantages over the conventionally adopted scheme of continuous injection were verified. The results show that intermittent injection can significantly reduce the dosage of normal saline (reduced by 44.4%) with only a slight sacrifice of image quality (reduced by 8.7%, but still acceptable). The developed model and key findings in this work can help surgeons practice optimized IVOCT operations and potentially lead to improved designs of the IVOCT equipment.

Hemodynamics of Saline Flushing in Endoscopic Imaging of Partially Occluded Coronary Arteries

PURPOSE

Intravascular endoscopy can aid in the diagnosis of coronary atherosclerosis by providing direct color images of coronary plaques. The procedure requires a blood-free optical path between the catheter and plaque, and achieving clearance safely remains an engineering challenge. In this study, we investigate the hemodynamics of saline flushing in partially occluded coronary arteries to advance the development of intravascular forward-imaging catheters that do not require balloon occlusion.

METHODS

In-vitro experiments and CFD simulations are used to quantify the influence of plaque size, catheter stand-off distance, saline injection flowrate, and injection orientation on the time required to achieve blood clearance.

RESULTS

Experiments and simulation of saline injection from a dual-lumen catheter demonstrated that flushing times increase both as injection flow rate (Reynolds number) decreases and as the catheter moves distally away from the plaque. CFD simulations demonstrated that successful flushing was achieved regardless of lumen axial orientation in a 95% occluded artery. Flushing time was also found to increase as plaque size decreases for a set injection flowrate, and a lower limit for injection flowrate was found to exist for each plaques size, below which clearance was not achieved. For the three occlusion sizes investigated (90, 95, 97% by area), successful occlusion was achieved in less than 1.2 s. Investigation of the pressure fields developed during injection, highlight that rapid clearance can be achieved while keeping the arterial overpressure to < 1 mmHg.

CONCLUSIONS

A dual lumen saline injection catheter was shown to produce clearance safely and effectively in models of partially occluded coronary arteries. Clearance was achieved across a range of engineering and clinical parameters without the use of a balloon occlusion, providing development guideposts for a fluid injection system in forward-imaging coronary endoscopes.

Optimization Study of the Hemodynamics of Saline Flushing in Endoscopic Imaging of Chronic Total Occlusions (CTOs)

PURPOSE

In this study, in vitro experiments and computational fluid dynamic (CFD) simulations are used to expand the understand of the physics of saline flushing of a blocked artery to enable optical imaging. This process involves saline injection, mixing with blood, and advection of the mixture away from the region of interest to provide a clear optical path for imaging.

METHODS

CFD simulations are used as a rapid turn-around tool for the evolutionary design process of an endovascular catheter that combines imaging forward-viewing element with saline flushing lumens.

RESULTS

A novel design and control technique is developed that provides the method to regulate the pressure in a blocked artery during saline flushing, so only small deviations from physiological pressure values are exerted on the damaged artery wall at any time, minimizing risk of rupture. In vitro experiments demonstrate the optical clearing process in phantoms simulating chronic total occlusions (CTOs) in coronary arteries with an opaque blood surrogate being removed by saline flushing. With the CFD compared by the experiments, parametric analyses of artery diameter and curvature, and flushing lumen diameter size were conducted to understand their impact on flushing times and pressures. Different plaque morphologies were studied to explore the feasibility of saline flushing in different CTO conditions.

CONCLUSIONS

A new catheter design is demonstrated to safely and effectively produce saline flushing, leading to a clear optical imaging field, and an improved technique is outlined that overcomes some practical challenges and limitations commonly encountered in angioscopy.

The Performance of a Spherical-tip Catheter for Stent Post-dilation: Finite Element Analysis and Experiments

At present, percutaneous coronary intervention (PCI) is the most effective treatment of coronary artery stenosis. However, in case post-dilation of the stent is needed, the tip of the commonly used post-dilation balloon catheter cannot always pass through the stent smoothly, especially when it is situated in the curved part of the vessel. To improve the performance of traditional post-dilation balloon catheter, a preliminary design of a novel catheter with a spherical-tip is proposed. Since the performance of this spherical-tip catheter is still unclear, in this study, finite element analysis (FEA) and experimental validation of blood vessel with different curvature radii were performed to test and evaluate the performance of the spherical-tip catheter design. The comparative results between the two types of catheters demonstrate that in the simulated post-dilation process, the spherical-tip catheter is easier to pass through the stent placed in the curved vessel without the deformation of the stent strut, and can theoretically reduce the operation time and improve the safety of the operation. Furthermore, the strong consistency between simulation and experiment indicates that the finite element (FE) model can be a helpful tool for future optimization and evaluation of novel catheters, so as to save time and budget in product development and reduce/replace animal studies.

Mechanism of pulsatile flushing technique for saline injection via a peripheral intravenous catheter

BACKGROUND

The underlying mechanism of pulsatile flushing technique has not been fully elucidated, and the partial understanding of the mechanism has been confined to hydrodynamic simulation, ignoring the dynamic interaction among the catheter, blood vessel, blood stream, and saline.

METHODS

The peripheral intravenous catheter and vein models and their internal flow fields were assessed using a commercial software. The parameters of both fluid and structural mechanics were calculated and compared in the push and pause phase. The effect of different flushing volumes per bolus before each pause (0.5, 1.0, 1.5, and 2.0 mL) were compared, respectively corresponding to group (A, B, C and D).

FINDINGS

In groups C and D, the wall shear stress value (≥2 Pa) and enhanced shear rates (peaks up to 10,000 s^-1) were higher in the vessel wall near the catheter tip, which may be at risk of vascular endothelial injury. Furthermore, extraluminal flushing might be attributed to the recirculation of jet from the catheter outlet. The vortices of all groups faded away in an extremely short period (≤0.1 s) if the push was suddenly discontinued. Finally, overlarge displacement of the catheter tip in groups C and D (0.91 and 1.1 mm, respectively) caused the peripheral intravenous catheters to angle with the venous wall.

INTERPRETATION

The pulsatile flushing technique can facilitate intra- and extraluminal flushing of peripheral intravenous catheters. Furthermore, an insufficient volume per bolus can lead to inefficient flushing, and an overdose of single push may cause mechanical endothelial injury.

The mechanistic causes of peripheral intravenous catheter failure based on a parametric computational study

Peripheral intravenous catheters (PIVCs) are the most commonly used invasive medical device, yet up to 50% fail. Many pathways to failure are mechanistic and related to fluid mechanics, thus can be investigated using computational fluid dynamics (CFD). Here we used CFD to investigate typical PIVC parameters (infusion rate, catheter size, insertion angle and tip position) and report the hemodynamic environment (wall shear stress (WSS), blood damage, particle residence time and venous stasis volumes) within the vein and catheter, and show the effect of each PIVC parameter on each hemodynamic measure. Catheter infusion rate has the greatest impact on our measures, with catheter orientation also playing a significant role. In some PIVC configurations WSS was 3254 times higher than the patent vein, and blood damage was 512 times greater, when compared to control conditions. Residence time is geometry-dependent and decreases exponentially with increasing insertion angle. Stasis volume decreased with increasing infusion rate and, to a lesser degree, insertion angle. Even without infusion, the presence of the catheter changes the flow field, causing low velocity recirculation at the catheter tip. This research demonstrates how several controllable factors impact important mechanisms of PIVC failure. These data, the first of their kind, suggest limiting excessive infusion rates in PIVC.