Researcher:
Bozkaya, Tijen Alkan

Profile Picture
ORCID

Job Title

Doctor

First Name

Tijen Alkan

Last Name

Bozkaya

Name

Name Variants

Bozkaya, Tijen Alkan

Email Address

Birth Date

Filters

2017 - 201922020 - 20212

Advanced Search

Filter by

Settings

Researcher Of Publications: search.filters.isAuthorOfPublication.914fcd83-6583-4c3f-984b-11f44384497c

Search Results

Now showing 1 - 4 of 4
  • Placeholder
    PublicationMetadata only
    Correlation between blood lactate and regional cerebral oxygen saturation in complex cardiac pathology neonates and infants: the effect on extubation time and ICU stay
    (Scientific Publishers of India, 2017) Karaaslan, Pelin; Gokay, Banu Vural; Hizarci, Burcu; Ozyuksel, Arda; Akcevin, Atif; N/A; N/A; N/A; Ünlükaplan, Aytekin; Darçın, Kamil; Bozkaya, Tijen Alkan; Doctor; Teaching Faculty; Doctor; N/A; School of Medicine; N/A; Koç University Hospital; N/A; Koç University Hospital; N/A; 203217; 143793
    Background: The monitoring of regional cerebral O2 saturation (rSO2) with near-infrared spectroscopy (NIRS) is a noninvasive technique to measure tissue oxygenation in the brain. It may be an effective monitoring technique in the early diagnosis of pre-, intra- and post-operative insufficient oxygen supply to the brain in surgery for congenital heart diseases. In pediatric patients, a variety of clinical and laboratory parameters, including serum lactate and regional cerebral oxygen saturation, may be helpful in monitoring global tissue and cerebral oxygen delivery and consumption. Aim: Our study was designed to investigate whether there is a correlation between the NIRS scores and serum lactate levels during congenital heart surgery. Our secondary objective was to define the predictive value of this correlation on the duration of extubation and intensive care unit stay. Method: A total of 82 successive neonatal and infant patients with complex cardiac pathologies were enrolled in the study. Blood lactate levels and NIRS values were measured during the phases of anesthesia induction, sternotomy, cannulation, onset of CPB, the beginning of aortic cross-clamping and the end of the CPB. Study Design: Prospective randomized Results: Patients with normal rSO2 /normal lactate during the operation represented the largest percentage of patients during anesthesia induction (n=50, 60.9%) and sternotomy (n=54, 65.8%). The only negative correlation between lactate and rSO2 was detected during anesthesia induction. The time to extubation and the stay in the intensive care unit were longer in patients with low rSO2 values during anesthesia induction and sternotomy. In the same periods, elevated lactate levels were associated with longer time to extubation and intensive care unit stay than the patients with normal lactate levels. Conclusion: In our study, no correlation was demonstrated between NIRS scores and serum lactate levels in children during congenital heart surgery, except for anesthesia induction. The only negative correlation between the decrease in NIRS scores and the increase in serum lactate levels was observed during anesthesia induction. This result indicated that cerebral NIRS monitoring cannot be used as an indicator of global hypoperfusion in the same way as lactate.
  • Placeholder
    PublicationMetadata only
    Computational pre-surgical planning of arterial patch reconstruction: parametric limits and in vitro validation
    (Springer, 2018) Salihoglu, Ece; Yerebakan, Can; Department of Mechanical Engineering; Department of Molecular Biology and Genetics; Department of Mechanical Engineering; N/A; Lashkarinia, Seyedeh Samaneh; Pişkin, Şenol; Pekkan, Kerem; Bozkaya, Tijen Alkan; Researcher; Researcher; Faculty Member; Doctor; Department of Molecular Biology and Genetics; Department of Mechanical Engineering; College of Engineering; College of Engineering; College of Engineering; N/A; N/A; N/A; N/A; Koç University Hospital; N/A; 148702; 161845; 143793
    Surgical treatment of congenital heart disease (CHD) involves complex vascular reconstructions utilizing artificial and native surgical materials. A successful surgical reconstruction achieves an optimal hemodynamic profile through the graft in spite of the complex post-operative vessel growth pattern and the altered pressure loading. This paper proposes a new in silico patient-specific pre-surgical planning framework for patch reconstruction and investigates its computational feasibility. The proposed protocol is applied to the patch repair of main pulmonary artery (MPA) stenosis in the Tetralogy of Fallot CHD template. The effects of stenosis grade, the three-dimensional (3D) shape of the surgical incision and material properties of the artificial patch are investigated. The release of residual stresses due to the surgical incision and the extra opening of the incision gap for patch implantation are simulated through a quasi-static finite-element vascular model with shell elements. Implantation of different unloaded patch shapes is simulated. The patched PA configuration is pressurized to the physiological post-operative blood pressure levels of 25 and 45 mmHg and the consequent post-operative stress distributions and patched artery shapes are computed. Stress-strain data obtained in-house, through the biaxial tensile tests for the mechanical properties of common surgical patch materials, Dacron, Polytetrafluoroethylene, human pericardium and porcine xenopericardium, are employed to represent the mechanical behavior of the patch material. Finite-element model is experimentally validated through the actual patch surgery reconstructions performed on the 3D printed anatomical stenosis replicas. The post-operative recovery of the initially narrowed lumen area and post-optortuosity are quantified for all modeled cases. A computational fluid dynamics solver is used to evaluate post-operative pressure drop through the patch-reconstructed outflow tract. According to our findings, the shorter incisions made at the throat result in relatively low local peak stress values compared to other patch design alternatives. Longer cut and double patch cases are the most effective in repairing the initial stenosis level. After the patch insertion, the pressure drop in the artery due to blood flow decreases from 9.8 to 1.35 mm Hg in the conventional surgical configuration. These results are in line with the clinical experience where a pressure gradient at or above 50 mm Hg through the MPA can be an indication to intervene. The main strength of the proposed pre-surgical planning framework is its capability to predict the intraoperative and post-operative 3D vascular shape changes due to intramural pressure, cut length and configuration, for both artificial and native patch materials.
  • Thumbnail Image
    PublicationOpen Access
    A 19-year-old pregnant woman with pulmonary hypertension with progressive dyspnea
    (Elsevier, 2021) Avcı, Burçak Kılıçkıran; Tok, Özge Özden; Öngen, Zeki; Bozkaya, Tijen Alkan; Kalangos, Afksendiyos; Doctor; Faculty Member; School of Medicine; Koç University Hospital; N/A; 286247
    Case presentation: a 19-year-old pregnant woman at week 32 of gestation was referred to our clinic with progressive shortness of breath for the further evaluation and treatment of high-risk pregnancy. Her complaints had been existing since her childhood. Two years prior to her admission, she had been diagnosed with heart failure with preserved ejection fraction due to cardiomyopathy and associated pulmonary hypertension. The patient had no family history of any cardiac disease. She had never smoked or drunk alcohol. Her clinical condition had deteriorated progressively with the pregnancy.
  • Thumbnail Image
    PublicationOpen Access
    Patient-specific hemodynamics of new coronary artery bypass configurations
    (Springer, 2020) Pişkin, Senol; Tenekecioğlu, Erhan; Karagöz, Haldun; N/A; Department of Mechanical Engineering; Rezaeimoghaddam, Mohammad; Oğuz, Gökçe Nur; Lashkarinia, Seyedeh Samaneh; Pekkan, Kerem; Ateş, Mehmet Şanser; Bozkaya, Tijen Alkan; Researcher; Faculty Member; Doctor; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; College of Engineering; Koç University Hospital; N/A; N/A; N/A; 161845; N/A; N/A
    Purpose: this study aims to quantify the patient-specific hemodynamics of complex conduit routing configurations of coronary artery bypass grafting (CABG) operation which are specifically suitable for off-pump surgeries. Coronary perfusion efficacy and local hemodynamics of multiple left internal mammary artery (LIMA) with sequential and end-to-side anastomosis are investigated. Using a full anatomical model comprised of aortic arch and coronary artery branches the optimum perfusion configuration in multi-vessel coronary artery stenosis is desired. Methodology: two clinically relevant CABG configurations are created using a virtual surgical planning tool where for each configuration set, the stenosis level, anastomosis distance and angle were varied. A non-Newtonian computational fluid dynamics solver in OpenFOAM incorporated with resistance boundary conditions representing the coronary perfusion physiology was developed. The numerical accuracy is verified and results agreed well with a validated commercial cardiovascular flow solver and experiments. For segmental performance analysis, new coronary perfusion indices to quantify deviation from the healthy scenario were introduced. Results: the first simulation configuration set;-a CABG targeting two stenos sites on the left anterior descending artery (LAD), the LIMA graft was capable of 31 mL/min blood supply for all the parametric cases and uphold the healthy LAD perfusion in agreement with the clinical experience. In the second end-to-side anastomosed graft configuration set;-the radial artery graft anastomosed to LIMA, a maximum of 64 mL/min flow rate in LIMA was observed. However, except LAD, the obtuse marginal (OM) and second marginal artery (m2) suffered poor perfusion. In the first set, average wall shear stress (WSS) were in the range of 4 to 35 dyns/cm(2)for in LAD. Nevertheless, for second configuration sets the WSS values were higher as the LIMA could not supply enough blood to OM and m2. Conclusion: the virtual surgical configurations have the potential to improve the quality of operation by providing quantitative surgical insight. The degree of stenosis is a critical factor in terms of coronary perfusion and WSS. The sequential anastomosis can be done safely if the anastomosis angle is less than 90 degrees regardless of degree of stenosis. The smaller proposed perfusion index value,O(0.04 - 0) x 10(2), enable us to quantify the post-op hemodynamic performance by comparing with the ideal healthy physiological flow.