Further Experimental Evidence that Pulmonary Capillary Pressures Do Not Reflect Cyclic Changes in Left Atrial Pressure (Mitral

Wedged catheter pressures (PC) were compared with those in the aorta, left atrium, and pul-monary artery before and after production of mitral stenosis, insufficiency, and pulmonary em-bolism. In general it was found that "PC " pressures follow closely changes in left atrial pressures even when pulmonary artery pressure changes in an opposite direction (for example, pulmonary embolism). However, properly recorded "PC " pressure pulses did not display the large cyclic pressure variations recorded from the left atrium during mitral stenosis and insufficiency. It is concluded that pressures recorded through a properly wedged catheter represent the constant pulmonary capillary pressure but do not reflect cyclic pressure variations in the left atrium. IN A previous communication1 experimentalevidence was presented that a catheterproperly wedged into a peripheral pulmon-ary artery records a rather constant pressure, generally a little higher than that in the left atrium. Therefore, such pressures can be fairly taken as an index of pulmonary capillary pres-sure (PCP). However, it was questioned whether phasic left atrial pressures can be transmitted through capillaries to such a cath-eter, as others have believed.2"5 Evidence was presented that when phasic systolic variations are recorded through a wedged catheter they are caused by transmission of pulmonary ar-terial pressure to the catheter tip. Instead of giving information regarding left atrial pres-sures they must be regarded as artefacts from improper lodgment of a catheter. These studies did not exclude the possibility that large pre