Development of arterial blood pressure in the chick embryo

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Abstract
It has been possible to record the blood pressure in chick embryos of all ages using micropipettes for cannulation. In addition to a transducer and electronic equipment as generally used for pressure measurements, 5 high-gain d-c operational amplifiers were employed to correct electronically for the damping caused by the small size of the micropipettes. A pulsatile arterial pressure was recordable in embryos as young as 46-hr incubation age (22 somites) and was found to average 0.4/0.3 mm Hg. The pressure rose to an average of 1.2/0.8 mm Hg at the end of the 3rd incubation day, remained nearly constant during the 4th day and hereafter continued to rise to an average of 36/22 mm Hg during the 20th day. During the 1st day after hatching the average pressure was 56/38 mm Hg. A linear relationship was found to exist between systolic pressure and embryonic weight after the 4th day of incubation. Ventricular pressures were measured in embryos as young as 5 days incubation age. The tracings were characteristic of those recorded in cardiac ventricles with diastolic pressures approaching zero, indicating that an arterial valve mechanism is operativeat an early stage ofdevelopment.