Postnatal Development of a Left-Right Atrial Pressure Gradient

¹ From the Kerckhoff Laboratories of the Biological Sciences, California Institute of Technology, Pasadena, California

The mean left and right atrial pressures were measured in six groups of 10 kittens each. One group was examined between the 12th and 24th hour after birth, one group after 3 days, after 1 week, 2 weeks, 1 month and 2 months. The left and right atrial pressures were almost equal in the first group. With age an increasing left to right pressure gradient developed. In the oldest group the pressure in the left atrium was almost twice as great as in the right. Parallel with the pressure gradient a difference developed in the wall thicknesses of the left and right ventricles. At birth the ventricular walls were of about equal thickness; at age 2 months the left ventricle wall was more than twice as thick as the right. The relationship between ventricle wall thicknesses and atrial pressures is discussed.