Sonospirometry: a new method for noninvasive estimation of mean right atrial pressure based on two-dimensional echographic measurements of the inferior vena cava during measured inspiration.

A noninvasive method of estimating mean right atrial pressure would be useful in evaluating hemodynamics and calculating pulmonary pressures by Doppler echocardiography. An electronic pressure gauge was built and tested for measurement of inspiratory pressures during two-dimensional echocardiography to quantitate the diameter of the inferior vena cava. Thirty-one studies were made in 27 alert, informed, consenting patients with an in-place pulmonary artery catheter having right atrial ports. Inferior vena cava diameter was measured in successive 10 mm segments distal to the right atrial-inferior vena cava junction on images obtained while the patient suspended breathing at full inspiration and during each 4 mm Hg increment of a calibrated inspiratory maneuver. Results show that the segment between 5 and 30 mm distal to the right atrial-inferior vena cava junction was the region most responsive to increasing inspiratory pressure. In this segment, the inspiratory pressure required to decrease the inferior vena cava diameter to greater than or equal to 85% of the difference between its maximal (suspended full inspiration) and minimal (over the entire inspiratory maneuver) values was similar or equal to the mean right atrial pressure (measured from the pulmonary artery catheter) (r = 0.87, SEE = 2.9 mm Hg). Minimal inferior vena cava diameter was directly related to mean right atrial pressure (r = 0.56); the minimal to maximal inferior vena cava diameter ratio was inversely related to mean right atrial pressure (r = -0.57). Maximal inferior vena cava diameter and the absolute (measured) amount of inferior vena cava diameter decrease correlated weakly with mean right atrial pressure.(ABSTRACT TRUNCATED AT 250 WORDS)