Researcher:
Yılmaz, Bahar Dikmen

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Undergraduate Student

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Bahar Dikmen

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Yılmaz

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Yılmaz, Bahar Dikmen

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20132

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    Adaptation dynamics measures in simultaneously recorded pattern electroretinograms and visual evoked responses
    (Institute of Electrical and Electronics Engineers (IEEE), 2013) Özdamar, Özcan; Villalon, Oscar; Bohórquez, Jorge; N/A; Yılmaz, Bahar Dikmen; Undergraduate Student; School of Medicine; N/A
    In this study a new methodology to measure adaptation dynamics of simultaneously recorded Pattern ElectroRetinoGrams (PERG) and Visual Evoked Potentials (PVEP) were developed. Monocular PERGs and VEPs were recorded in response to randomly delivered bursts (1 through 8) of visual reversal displays in ten adult normal subjects. Reversals were 102ms apart and reversal bursts were separated with 510ms intervals. Stimuli were horizontal gratings presented on a custom made display designed using fast onset/offset white LEDs. Responses to individual reversals were obtained by simultaneous two channel continuous recordings. Data were processed offline by selective averaging based on burst size followed by subtraction and shifting of the previous consecutive burst responses from the last consecutive burst response. The results showed that PERG (N35-P50) component showed little change (no adaptation) while (P50-N95) reduced 20% in the second reversal (adaptation <200ms). VEP (N75- P100) and (P100-N135) components, on the other hand, exhibited dramatic reduction (35%) in the first four reversals (adaptation<500ms) before it stabilized. The methodology presented provides rapidly acquired and repeatable quantitative measures of visual adaptation dynamics for different structures of the visual pathway and may be useful in early detection of various neuroophthalmic diseases.
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    PublicationOpen Access
    Shear stress-induced improvement of red blood cell deformability
    (IOS Press, 2013) Meiselman, Herbert J.; Meram, Ece; Yılmaz, Bahar Dikmen; Baş, Ceren; Ataç, Nazlı; Yalçın, Özlem; Başkurt, Oğuz Kerim; Faculty Member; Researcher; School of Medicine; N/A; N/A; N/A; N/A; 218440; 2389
    Classically, it is known that red blood cell (RBC) deformability is determined by the geometric and material properties of these cells. Experimental evidence accumulated during the last decade has introduced the concept of active regulation of RBC deformability. This regulation is mainly related to altered associations between membrane skeletal proteins and integral proteins, with the latter serving to anchor the skeleton to the lipid matrix. It has been hypothesized that shear stress induces alterations of RBC deformability: the current study investigated the dynamics of the transient improvement in deformability induced by shear stress at physiologically-relevant levels. RBC were exposed to various levels of shear stress (SS) in a Couette type shearing system that is part of an ektacytometer, thus permitting the changes in RBC deformability during the application of SS to be monitored. Initial studies showed that there is an increase in deformability of the RBC subjected to SS in the range of 5–20 Pa, with kinetics characterized by time constants of a few seconds. Such improvement in deformability, expressed by an elongation index (EI), was faster with higher levels of SS and hence yielded shorter time constants: absolute values of EI increased by 3–8% of the starting level. Upon the removal of the shear stress, this response by RBC was reversible with a slower time course compared to the increase in EI during application of SS. Increased calcium concentration in the RBC suspending medium prevented the improvement of deformability. It is suggested that the improvement of RBC deformability by shear forces may have significant effects on blood flow dynamics, at least in tissues supplied by blood vessels with impaired vasomotor reserve, and may therefore serve as a compensating mechanism for the maintenance of adequate microcirculatory perfusion.