Blood flow dynamics reflect degree of outflow tract banding in Hamburger–Hamilton stage 18 chicken embryos

Abstract

Altered blood flow during embryonic development has been shown to cause cardiac defects; however, the mechanisms by which the resulting haemodynamic forces trigger heart malformation are unclear. This study used heart outflow tract banding to alter normal haemodynamics in a chick embryo model at HH18 and characterized the immediate blood flow response versus the degree of band tightness. Optical coherence tomography was used to acquire two-dimensional longitudinal structure and Doppler velocity images from control (n ¼ 16) and banded (n ¼ 25, 6-64% measured band tightness) embryos, from which structural and velocity data were extracted to estimate haemodynamic measures. Peak blood flow velocity and wall shear rate (WSR) initially increased linearly with band tightness ( p , 0.01), but then velocity plateaued between 40% and 50% band tightness and started to decrease with constriction greater than 50%, whereas WSR continued to increase up to 60% constriction before it began decreasing with increased band tightness. Time of flow decreased with constriction greater than 20% ( p , 0.01), while stroke volume in banded embryos remained comparable to control levels over the entire range of constriction ( p . 0.1). The haemodynamic dependence on the degree of banding reveals immediate adaptations of the early embryonic cardiovascular system and could help elucidate a range of cardiac adaptations to gradually increased load.

Blood flow through the embryonic heart outflow tract during cardiac looping in HH13–HH18 chicken embryos

“…A summary of optical, structural OCT and Doppler OCT images acquired at each stage is shown in figure 1. The overall analysis procedure is very similar to the process we reported for blood flow at HH18 in surgically manipulated and control embryos [33]. This process uses structural data to convert vertical velocity from the Doppler phase data to absolute blood flow velocity magnitude, and then employs Poisseuille's equation to estimate peak Q, SV and WSR.…”

“…Doppler flow phase images were generated together with simultaneous structural images in post-processing by calculating the phase differences between two adjacent A-scans in a B-scan. Doppler velocities (vertical velocities, V Z ) were then computed from phase data, and the accuracy of these velocities was recently confirmed with a syringe pump [33]. A thermocouple-controlled heating pad surrounding a ceramic cup filled with water was used to maintain temperature in a plastic box during acquisition.…”

“…Our custom-made OCT system has been previously detailed and used to image embryonic chicken heart motion and blood flow dynamics [32,33]. Briefly, the system has a spectral domain configuration consisting of a superluminescent diode centred at 1325 nm from Thorlabs Inc. (Newton, NJ, USA) and a 1024 pixel, 92 kHz maximal line-scan rate infrared InGaAs line-scan camera from Goodrich Inc. (Charlotte, NC, USA).…”

“…Phase shift OCT data within the sampling area were converted to vertical velocity (V Z ) values that were averaged and filtered as previously described [33]. We then calculated the magnitude of the blood flow velocity (V ) using:…”

Dynamic imaging and quantitative analysis of cranial neural tube closure in the mouse embryo using optical coherence tomography

“…Embryology is a major research area where OCT shows great promise as a high-resolution unlabeled imaging tool [31][32][33]. With the primary focus on the cardiovascular development and abnormalities, OCT has been reported able to reveal detailed structures of the embryonic heart comparable to histology [34][35][36], to capture four-dimensional dynamic cardiac activities [37][38][39], to quantify biomechanics of the heart tube [40][41][42], to assess cardiac hemodynamics [43][44][45], to characterize novel mutant heart phenotypes [46][47][48], and to investigate cardiac responses to physical and chemical manipulations [49][50][51][52]. Focusing on the mouse model, our group has combined OCT with live embryo culture to establish a number of structural and functional imaging methods [39,45,48,[53][54][55], suggesting an important role of OCT for in vivo analysis of the mammalian embryo.…”