Studies on Starling's Law of the Heart: IV. Observations on the Hemodynamic Functions of the Left Atrium in Man

Abstract

The hemodynamic functions of the left atrium were studied in 26 patients with disturbances of left ventricular function and in 16 subjects without any abnormalities of the cardiovascular system. Attention was directed to the effect of atrial systole on the relationship between mean left atrial pressure (MLAP) and left ventricular end-diastolic pressure (LVEDP). This relationship was considered to be a meaningful one in view of the importance of the LVEDP in determining the characteristics of ventricular contraction, and of the MLAP in determining the symptoms of left heart failure. In the subjects with normal cardiovascular systems, LVEDP-MLAP averaged 0.2 mm. Hg, but this value averaged 9.0 mm. Hg in patients with left ventricular disease, in whom left atrial contraction elevated LVEDP while permitting MLAP to remain at a significantly lower level. The magnitude of the pressure difference between LVEDP and MLAP was found to be dependent on the characteristics of atrial contraction; the height of the "a" wave appeared to be related to the atrial pressure prior to the onset of atrial contraction. The elevation of atrial pressure produced by atrial systole was found to vary directly with the time interval between the onset and the peak of the "a" wave and to vary inversely with the time interval between the peak of the "a" wave and the onset of ventricular contraction. Evidence was presented that in intact human subjects the characteristics of left atrial and left ventricular contraction are functions of the pressures in these chambers prior to the onset of their contraction, thus lending further support to the concept that Starling's law is operative in the human heart.