Estimation of transmural cardiac pressures during ventilation with PEEP

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Abstract
Assessment of ventricular performance during positive end-expiratory pressure (PEEP) requires accurate measurement of trans mural cardiac pressures. The influence of PEEP on the atrial and juxtacardiac pressures (estimated by different methods) was investigated in 8 dogs. Left atrial pressure was measured by hydraulic and transducer-tipped catheter systems. Juxtacardiac pressure was estimated by an esophageal balloon and by air- an fluid-filled mediastinal wafer sensors. The supine canine heart was observed radiographically to lift and tilt during PEEP subjecting the left atrial catheters and the fluid-filled mediastinal wafer to a hydrostatic pressure increase. The esophageal balloon seriously underestimated the pressure increment occurring during the application of PEEP in the supine (but not prone) position, perhaps because mediastinal weight was lifted from the esophagus during lung distension. Similar phenomena were also observed in 3 human subjects. Lung distension lifts and tilts the heart in a supine preparation causing a hydrostatic increase of intracavitary pressure and attenuation of the esophageal pressure increment. These effects help to account for the apparent alterations of ventricular compliance and performance previously attributed to PEEP.