Interrelations of Pulmonary Arterial, ‘Capillary’ and Left Atrial Pressures Under Experimental Conditions

Abstract

Pressure from a catheter impacted in a peripheral pulmonary artery was compared with that in the left atrium and pulmonary artery. Pulmonary capillary (PC) pressures normally are constant throughout the cardiac cycle except for minor oscillations at the onset and end of ventricular systole. Instantaneous pressures measured at the end of systole revealed that PC pressure exceeds left atrial pressures (1.5-3.7 mm. Hg). PC pressure showed changes corresponding to exptl. alterations of left atrial pressure, but were not affected by exptl. changes in pulmonary or aortic pressures. Curves displaying phasic variations similar to those attributed to retrograde transmission of left atrial pressure can be recorded from normal dogs. In such curves instantaneous pressure exceeded that in the left atrium and the contour and time relations of waves from these 2 compartments did not agree. Under different exptl. conditions phasic pressure changes in PC pressure followed the trends of pulmonary arterial, not left atrial pressure, suggesting leakage of pressure around the catheter to its tip. Evidence was presented that withdrawal of oxygenated blood from a catheter by suction may not be a guarantee that such leakage has not occurred. The conclusion follows that in the estimation of pulmonary capillary pressures reliance can be placed only on catheter curves that are devoid of phasic changes.