Transesophageal echocardiographic dimensional analysis of four cardiac chambers during positive end-expiratory pressure.

The authors examined the effects of positive end-expiratory pressure (PEEP) on cardiac function by dimensional analysis of the four heart chambers using M-mode transesophageal echocardiography (TEE). The accuracy of cardiac output (CO) calculated from TEE was confirmed by its close correlation (r = 0.97) with CO, determined by the thermodilution technique. The reliability of TEE also was confirmed by excellent correlation (r = 0.95) between left ventricular end-diastolic (LVEDD) and end-systolic (LVESD) dimensions measured by the two-dimensional precordial echocardiography and those by TEE. With 10 cmH2O PEEP LVEDD decreased from its level during zero end-expiratory pressure (ZEEP), and the calculated stroke volume also decreased. These decreases were greater during 15 cmH2O PEEP, where heart rate increased slightly but significantly. Ejection fraction (EF) and fractional shortening (FS), as a whole, did not change significantly. Mean velocity of circumferential fiber shortening (mean Vcf) significantly increased and LVESD significantly decreased with PEEP. Although systolic blood pressure (SBP) significantly decreased, the (SBP-PEEP value)/LVESD ratio was not changed with PEEP. Such measures of left ventricular systolic function as EF, FS, mean Vcf, and (SBP-PEEP value)/LVESD were not decreased. Right ventricular end-diastolic dimension decreased with PEEP. Right atrial end-diastolic dimension began to decrease immediately after PEEP was initiated, whereas left atrial end-diastolic dimension began to decrease a few seconds later, suggesting that left ventricular preload decreased as a result of a decrease in right ventricular preload. The authors therefore conclude that CO was decreased as a result of the decrease in right and left ventricular preloads.