Alterations in pulse wave propagation reflect the degree of outflow tract banding in HH18 chicken embryos

Abstract

Hemodynamic conditions play a critical role in embryonic cardiovascular development, and altered blood flow leads to congenital heart defects. Chicken embryos are frequently used as models of cardiac development, with abnormal blood flow achieved through surgical interventions such as outflow tract (OFT) banding, in which a suture is tightened around the heart OFT to restrict blood flow. Banding in embryos increases blood pressure and alters blood flow dynamics, leading to cardiac malformations similar to those seen in human congenital heart disease. In studying these hemodynamic changes, synchronization of data to the cardiac cycle is challenging, and alterations in the timing of cardiovascular events after interventions are frequently lost. To overcome this difficulty, we used ECG signals from chicken embryos (Hamburger-Hamilton stage 18, ∼3 days of incubation) to synchronize blood pressure measurements and optical coherence tomography images. Our results revealed that, after 2 h of banding, blood pressure and pulse wave propagation strongly depend on band tightness. In particular, while pulse transit time in the heart OFT of control embryos is ∼10% of the cardiac cycle, after banding (35% to 50% band tightness) it becomes negligible, indicating a faster OFT pulse wave velocity. Pulse wave propagation in the circulation is likewise affected; however, pulse transit time between the ventricle and dorsal aorta (at the level of the heart) is unchanged, suggesting an overall preservation of cardiovascular function. Changes in cardiac pressure wave propagation are likely contributing to the extent of cardiac malformations observed in banded hearts.

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

“…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).…”

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

“…In addition to structural images, this system can generate simultaneous Doppler flow phase images in post-processing by calculating the phase differences between two adjacent A-scans in a B-scan. Our group has previously used a similar system to image the embryonic chicken heart motion and blood flow dynamics [13,14,17,18]. Temperature during acquisition was maintained with a thermocouple-controlled heating pad surrounding the egg in a ceramic cup filled with water, which was enclosed in a plastic box.…”

“…OTB increases pressure wave propagation speed, while rsif.royalsocietypublishing.org J. R. Soc. Interface 11: 20140643 decreasing peristaltic-like patterns of OFT wall motion [13]. The suture in OTB physically anchors the OFT to surrounding membrane tissues, making the wall effectively stiffer and less compliant with increased band tightness.…”

“…We used a surgical intervention, cardiac outflow tract banding (OTB), to alter haemodynamic conditions through the chick embryo heart. In OTB (also called 'banding' here for simplicity), a suture band is tied around the OFT to decrease the cross-sectional area and restrict the motion of the OFT wall, resulting in increased resistance to flow, peak ventricular pressure [8,13] and blood flow velocities [14]. The high-shear and high-pressure flow conditions introduced by OTB have been shown to result in a wide spectrum of heart defects in the chick embryo [2,4,7,8,15].…”

“…OCT provides a combination of structural and Doppler images with the same spatial and time resolution, which makes OCT a valuable imaging technique to study embryonic blood flow haemodynamics [14,[16][17][18][19]. Furthermore, OTB band tightness can also be measured directly from structural OCT images [13]. OCT detects light reflected back from a low coherence light source to capture structure, and blood flow velocity is then calculated from the Doppler frequency shift when backscattered light from moving particles either adds or subtracts from the fixed Doppler frequency [20].…”