Relationship of simultaneous atrial and ventricular pressures in stage 16-27 chick embryos.

Ventricular filling is determined by a dynamic balance between atrial and ventricular load and function. The embryonic cardiovascular system undergoes simultaneous growth and morphogenesis at the cellular, tissue, and organ levels to match the embryo's geometrically increasing metabolic demands. As part of our long-term investigation of atrial/ventricular coupling during primary cardiac morphogenesis, we defined the relationship between simultaneous atrial and ventricular pressures in the stage 16-27 white Leghorn chick embryo. We measured atrial and ventricular blood pressures with servo-null micropressure systems and sampled analog waveforms digitally at 500 Hz. Peak atrial pressure increased geometrically from 0.38 +/- 0.03 to 1.21 +/- 0.17 mmHg, while ventricular end-diastolic pressure increased linearly from 0.18 +/- 0.03 to 0.55 +/- 0.04 mmHg. The passive and active mean pressure gradients increased from 0.23 +/- 0.04 and 0.20 +/- 0.03 mmHg at stage 16 to 0.52 +/- 0.10 and 0.62 +/- 0.11 mmHg at stage 27, respectively. The atrioventricular pressure gradients were similar for stages 16, 18, and 21, then increased to stage 27. This diastolic pressure gradient identifies the atrioventricular orifice and developing endocardial cushions as a site of flow resistance that may influence both ventricular filling and chamber morphogenesis.

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