Observations on the “effective ” Pressure in the Right and Left Auricles By

T HE term “ effective pressure ” has been aptly applied by Henderson and Barringer l to the difference between intrathoracic and intra-auricular pressures (measured, to be exact, at the auriculo-ventricular valves immediately before ventricular diastole) . That this represents the actual pressure brought into play in ventricular filling seems plausible because, as may be inferred from experiments on a recently stopped heart, the intraventricular pressure at the beginning of diastole probably nearly approximates the intrathoracic pressure. To these authors also belongs the credit of having shown that when this “ effective pressure ” is great enough, i.e., becomes “critical,” the heart acts in a uniform manner, so that the volume curves of the ventricles become “ superimposable.” In an earlier communication Henderson2 pointed out that the effective venous pressures could not be considered “ critical” unless they equalled at least 3 mm. of mercury, while, in a recent communication with Barringer, 50 mm. of water is regarded as a critical level. A re-study of many normal volume records taken in connection with another research3 confirm, in the main, the observations of Henderson and Barringer, but indicate that a higher pressure than they report should be regarded as “critical” for the heart. Without launching into details, the results showed that as the venous pressure increased up to 40 or 75 mm. of water, the