11TH INTERNATIONAL SYMPOSIUM ON PARTICLE IMAGE VELOCIMETRY Santa Barbara, California, September 14-16, 2015
Characterization of pulsatile wall shear stress at the vitelline artery during early embryonic development Fazil Emre Uslu1, Selda Goktas1, William Kowalski2, Bradley B. Keller2, Kerem Pekkan1,3 1
Mechanical Engineering, Koc University, Istanbul, Turkey
[email protected] 2 School of Medicine, University of Louisville, Louisville, USA 3 Department of Biomedical and Mechanical Engineering, Carnegie Mellon University, Pittsburgh, USA ABSTRACT Empirical evidence suggests that the hemodynamic forces and vascular stresses influence the growth and morphogenesis of the embryonic cardiovascular system. Due to the insufficient time-resolved in vivo data obtained throughout the embryonic growth, quantitative levels of hemodynamic loading is still uncertain [1,2]. A novel long-term time-lapse imaging method, based on optical coherence tomography (OCT), was used to investigate the simultaneous blood velocity and morphmetric data in the chicken embryo[3]. To acquire the velocity profile, time-resolved OCT-PIV technique is used and red blood cells were used as particles. The OCT system (Thorlabs Spectral Domain Ganymede, Thorlabs, Inc., NJ) was used with an environmental chamber to maintain physiological conditions of the embryo and Imager sCMOS camera (LaVision, Inc., Germany). Velocity analyses were performed for three stages of chicken embryos including HH16, HH17.5 and HH19. For each stage, 3-5 embryos were used to find the velocity profiles at each stage. First, data set including 6-7 pulsatile cardiac cycles was recorded with 67 fps. Velocity vectors were obtained with time series of single frames PIV method and multi-pass interrogation window (with decreasing size) by using DaVis 8.1.0 software (LaVision, Inc., Germany).
Mean Velocity [mm/s]
HH 17.5 3 2,5 2 1,5 1 0,5 0
0
0,05
0,1
0,15
0,2
0,25
0,3
0,35
0,4
-‐0,5 -‐1
A
B
Time [s] C
Figure 1. (A) Raw image of vessel obtained from OCT-PIV (B) Velocity vectors in the vessel acquired by PIV postprocessing (C) Phase-locked average of a cardiac cycle at stage HH17,5. A representative average cardiac velocity waveform of each embryo was obtained by the phase-locked average of 6-7 pulsatile cardiac cycles . The phase-locked average of flow waveforms of all embryos, from the corresponding embryonic stage was used to determine
1
11TH INTERNATIONAL SYMPOSIUM ON PARTICLE IMAGE VELOCIMETRY Santa Barbara, California, September 14-16, 2015 the embryonic-stage specific cardiac waveforms. Velocity profiles to use for Wall Shear Stress (WSS) are correlated by the cardiac cycle periods of the embryos, percentage backflow and Oscillatory Shear Index (OSI).
A
B
Figure 2. (A) Periods of cardiac cycles at 3 different stages (B) OSI at 3 different stages. Wall Shear Stress (WSS) of embryos at three different stages are calculated with velocity data and growth data acquired by the OCT imaging by assumption of Poiseuille flow because the velocity data was showed parabolic profile and it was sufficient to WSS variation at different stages. For example it was seen that WSS increases from HH16 to HH17.5 and decreases slightly from HH17.5 to HH19. These mechanical indices, including the pressure variation acquired through a servo null pressure measurement systems are correlated with vascular growth data acquired by the OCT imaging.
Figure 3. WSS results obtained from velocity and growth values at three different stages. Possibility of further statistical correlation is investigated with the in vitro reverse transcription polymerase chain reaction (RT-PCR) data to track the genetic activity associated with the growth and remodeling of the embryonic arterial walls. The WSS results obtained from RT-PCR analyses showed strong similarity with the WSS trends obtained from microscopic OCT particle image velocimetry. REFERENCES [1] Davis, A., Izatt, J., and Rothenberg, F. (2009). Quantitative measurement of blood flow dynamics in embryonic vasculature using spectral Doppler velocimetry. Anat Rec (Hoboken) 292, 311-319. doi: 10.1002/ar.20808 [2] Poelma, C., Vennemann, P., Lindken, R., and Westerweel, J. (2008). In vivo blood flow and wall shear stress measurements in the vitelline network. Exp Fluids 45 [3] Chen, C.-Y., Menon, P.G., Kowalski, W., and Pekkan, K. (2012). Time-resolved OCT-µPIV: a new microscopic PIV technique for noninvasive depth-resolved pulsatile flow profile acquisition. Experiments in Fluids 54, 1-9. doi: 10.1007/s00348-012-1426-x.
2
