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Experimental investigation into the effect of compliance of a mock aorta on cardiac performance.

ABSTRACT: Demand for heart transplants far exceeds supply of donated organs. This is attributed to the high percentage of donor hearts that are discarded and to the narrow six-hour time window currently available for transplantation. Ex-vivo heart perfusion (EVHP) provides the opportunity for resuscitation of damaged organs and extended transplantation time window by enabling functional assessment of the hearts in a near-physiologic state. Present work investigates the fluid mechanics of the ex-vivo flow loop and corresponding impact on cardiac performance. A mechanical flow loop is developed that is analogous to the region of the EVHP system that mimics in-vivo systemic circulation, including the body's largest and most compliant artery, the aorta. This investigation is focused on determining the effect of mock aortic tubing compliance on pump performance. A custom-made silicone mock aorta was developed to simulate a range of in-vivo conditions and a physiological flow was generated using a commercial ventricular assist device (VAD). Monitored parameters, including pressure, tube distension and downstream velocity, acquired using time-resolved particle imaging velocimetry (PIV), were applied to an unsteady Bernoulli analysis of the flow in a novel way to evaluate pump performance as a proxy for cardiac workload. When compared to the rigid case, the compliant mock aorta case demonstrated healthier physiologic pressure waveforms, steadier downstream flow and reduced energetic demands on the pump. These results provide experimental verification of Windkessel theory and support the need for a compliant mock aorta in the EVHP system.

SUBMITTER: Cameron K

PROVIDER: S-EPMC7549783 | biostudies-literature | 2020

REPOSITORIES: biostudies-literature

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Experimental investigation into the effect of compliance of a mock aorta on cardiac performance.

Cameron Katie K El Hassan Mouhammad M Sabbagh Reza R Freed Darren H DH Nobes David S DS

PloS one 20201012 10

Demand for heart transplants far exceeds supply of donated organs. This is attributed to the high percentage of donor hearts that are discarded and to the narrow six-hour time window currently available for transplantation. Ex-vivo heart perfusion (EVHP) provides the opportunity for resuscitation of damaged organs and extended transplantation time window by enabling functional assessment of the hearts in a near-physiologic state. Present work investigates the fluid mechanics of the ex-vivo flow ...[more]

PMID: 33044976

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Project description:Air compliance has been used effectively to stabilize fluidic instability resulting from a syringe pump. It has also been employed to measure blood viscosity under constant shearing flows. However, due to a longer time delay, it is difficult to quantify the aggregation of red blood cells (RBCs) or blood viscoelasticity. To quantify the mechanical properties of blood samples (blood viscosity, RBC aggregation, and viscoelasticity) effectively, it is necessary to quantify contributions of air compliance to dynamic blood flows in microfluidic channels. In this study, the effect of air compliance on measurement of blood mechanical properties was experimentally quantified with respect to the air cavity in two driving syringes. Under periodic on-off blood flows, three mechanical properties of blood samples were sequentially obtained by quantifying microscopic image intensity (<I>) and interface (?) in a co-flowing channel. Based on a differential equation derived with a fluid circuit model, the time constant was obtained by analyzing the temporal variations of ? = 1/(1-?). According to experimental results, the time constant significantly decreased by securing the air cavity in a reference fluid syringe (~0.1 mL). However, the time constant increased substantially by securing the air cavity in a blood sample syringe (~0.1 mL). Given that the air cavity in the blood sample syringe significantly contributed to delaying transient behaviors of blood flows, it hindered the quantification of RBC aggregation and blood viscoelasticity. In addition, it was impossible to obtain the viscosity and time constant when the blood flow rate was not available. Thus, to measure the three aforementioned mechanical properties of blood samples effectively, the air cavity in the blood sample syringe must be minimized (Vair, R = 0). Concerning the air cavity in the reference fluid syringe, it must be sufficiently secured about Vair, R = 0.1 mL for regulating fluidic instability because it does not affect dynamic blood flows.

Project description:This study investigated the impact of implanting TiO2-NPs within a membrane to minimize the influence of long-term operation on the membrane characteristics. Four poly vinyle chloride-titanium oxide (PVC-TiO2-NPs) membranes were prepared to create an ultrafiltration membrane (UF) that would effectively treat actual refinery wastewater. The hypothesis of this work was that TiO2-NPs would function as a hydrophilic modification of the PVC membrane and excellent self-cleaning material, which in turn would greatly extend the membrane's lifetime. The membranes were characterized via Fourier transforms infrared spectroscopy (FTIR), X-ray diffraction (XRD), energy dispersive X-ray (EDX), atomic force microscope (AFM), and scanning electron microscope (SEM). The removal efficiency of turbidity, total suspended solid (TSS), oil and grease, heavy metals and chemical oxygen demand (COD) were investigated. Contact angle (CA) reduced by 12.7% and 27.5% on the top and bottom surfaces, respectively. The PVC membrane with TiO2-NPs had larger mean pore size on its surface and more holes with larger size inside the membrane structure. The addition of TiO2-NPs could remarkably enhance the antifouling property of the PVC membrane. The pure water permeability (PWP) of the membrane was enhanced by 95.3% with an increase of TiO2 to 1.5 gm/100gm. The PWP after backwashing was reduced from 22.3% for PVC to 10.1% with 1.5 gm TiO2-NPs. The long-term performance was improved from five days for PVC to 23 d with an increase in TiO2-NPs to 1.5 gm. The improvements of PVC-TiO2-NPs long-term were related to the enhancement of the hydrophilic character of the membrane and increase tensile strength due to the reinforcement effect of TiO2-NPs. These results clearly identify the impact of the TiO2-NPs content on the long-term PVC/TiO2-NPs performance and confirm our hypothesis that it is possible to use TiO2-NPs to effectively enhance the lifetime of membranes during their long-term operation.

Project description:BackgroundTo investigate the ameliorated effects of an extract of Ginkgo biloba extract (GBE) on experimental cardiac remodeling in rats induced by acute cardiac infarction, and further explore the mechanism concentrated on myocardial type I collagen, transforming growth factor beta 1 (TGF-β1), matrix metalloproteinase 2 (MMP-2) and matrix metalloproteinase 9 (MMP-9), and provide the experimental data for clinical application of GBE.MethodsRats were divided into five groups (n = 20) as following: sham operation group (group A), acute myocardial infarction model group (group B), acute myocardial infarction model + aspirin (10 mg/kg) treatment group (group C), acute myocardial infarction model + captopril (20 mg/kg) treatment group (group D) and acute myocardial infarction model + Ginkgo biloba extract (100 mg/kg) treatment group (group E). The rat acute myocardial infarction model was reproduced by ligaturing the left anterior descending artery excluding the sham operation group which did not ligation only completed the operational process. Each group was further subdivided into treatment regimens lasting 4 weeks and 8 weeks. Immunohistochemistry and real-time polymerase chain reaction (PCR) methods were used to detect the protein expression and mRNA transcriptional levels of rat myocardial TGF-β1, type I collagen, MMP-2 and MMP-9.ResultsCompared with group B, regardless of the length of treatment (4 or 8 weeks), the TGF-β1, MMP-2 and MMP-9 mRNA transcriptional levels, and the protein expression levels of type I collagen, MMP-2 and MMP-9 in groups D, C and E were significantly decreased (P < 0.01). Furthermore, the mRNA expression levels of TGF-β1 in groups D, C and E were significantly lower after 8 weeks compared to after 4 weeks (P < 0.01), as were the expression levels of type I collagen in groups D, C and E (P < 0.05). There was no statistically significant difference in the protein expression levels of MMP-2 and MMP-9 between groups E and C.ConclusionsGBE could inhibit experimental rat myocardial remodeling after acute myocardial infarction via reduced transcription of TGF-β1, MMP-2 and MMP-9 genes and by the decreased expression of type I collagen, MMP-2 and MMP-9 proteins in myocardial cells.

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Experimental investigation into the effect of compliance of a mock aorta on cardiac performance.

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Experimental investigation into the effect of compliance of a mock aorta on cardiac performance.

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