Heart Rate–Dependent Characteristics of Diastolic Ventricular Filling in the Developing Chick Embryo

Abstract

The contributions of the early (passive) and late (active) components of ventricular filling have been reported to decrease and increase, respectively, during chick embryo cardiac development. We hypothesized that the observed changes in ventricular filling during early cardiac development results from a decrease in cycle length. We studied the effect of development and cycle length on atrioventricular inflow in 28 chick embryos, Hamilton-Hamburger stages 17, 24, and 26. Cycle length was perturbed (range 240-1040 ms) in ovo by transiently heating or cooling the sinus venosus. Atrioventricular inflow and dorsal aortic velocities were obtained by 20-MHz pulsed Doppler flowmeter and digitally recorded at 500 samples per second. Stroke volume was calculated from dorsal aortic velocity and crosssectional area. The atrioventricular inflow wave form was inte-The diastolic filling characteristics of the chick embryo ventricle change during developmental stages 12 through 27; the contributions of the early (passive) and late (active) components of ventricular filling have been reported to decrease and increase, respectively (1). Previous studies of altered embryonic heart rate using environmental temperature (I), cardiac pacing (2), and the thermal probe technique (3) have shown that early diastolic filling is heart rate dependent. This study further analyzes the differences in early ventricular filling velocities and flows resulting from heart rate perturbation. We found ventricular filling characteristics to be both developmentally determined and cycle length dependent. METHODSTwenty-eight fertile white Leghorn chicken eggs were incubated blunt end up at 38OC in a forced draft incubator to Hamburger-Hamilton stages 17 (n = 7, 3 d), 23-24 (n = 10, grated and partitioned by area and percentage of total into early (passive) and late (active) components using three methods. Regardless of method, the proportion of filling volume due to the early and late components was cycle length and stage dependent ( p < 0.05). The early and late filling volumes were large in the older embryos, and during cycle length decrease (heart rate increase) the early filling volume decrease was greater than the late filling volume decrease. When compared with the percentage of intrinsic heart rate, the percentage of stroke volume due to early filling decreased as heart rate increased and was greater in younger embryos at all heart rates. That due to late filling increased as the percentage of intrinsic heart rate increased. Ventricular filling characteristics are both developmentally determined and cycle length dependent. (Pediah. Res 37: 289-293, 1995) 4 d), and 25-26 (n = 11, 5 d) (4). Because of the similarity between adjacent stages, stage 23 (n = 1) and stage 24 (n = 9) embryos were consolidated into one group referred to as stage 24 (n = 10). Likewise, stages 25 (n = 2) and stage 26 (n = 9) were combined into stage 26 (n = 11). Eggs were placed in a heated sand bath (Bioengineering Department, Medical College of Georgia, Augusta, GA) under ...

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

“…At the earlier stages, as the ventricle fills with blood during the diastolic phase, it expands possibly exerting a suction pressure on blood flow in the OFT [55]. Endocardial cushions help to ensure unidirectional flow in the OFT by blocking the flow of blood during diastole.…”

Biomechanics of early cardiac development

“…Temperature variations lead to dramatic changes in cardiac rate in embryonic chicken, limulus, and fundulus larvae (Cohn, 1928; Parpart and Glaser, 1929; Cuneo et al, 1993; Phelan et al, 1995; Glaser, 1929; Crozier and Stier, 1927). Increasing temperature leads to an increase in cardiac rate and a decrease in stroke volume (Cuneo et al, 1993; Phelan et al, 1995).…”

“…Increasing temperature leads to an increase in cardiac rate and a decrease in stroke volume (Cuneo et al, 1993; Phelan et al, 1995). Similarly, an increase in cardiac rate achieved by pacing also reduces stroke volume (Benson et al, 1989) (see Table 3).…”