MAGNETIC-RESONANCE-IMAGING OF THE HEART DURING POSITIVE END-EXPIRATORY PRESSURE VENTILATION IN NORMAL SUBJECTS

Objectives: Magnetic resonance imaging was used to assess the effects of ventilation with positive end-expiratory pressure (PEEP) on cardiac volumes, especially on atrial volumes as well as to determine semiquantitative measurements of spatial interactions between heart, lungs and chest. Design: Prospective study with healthy volunteers undergoing mechanical ventilation with different levels of PEEP during magnetic resonance imaging. Setting: Magnetic resonance unit, Institute of Diagnostic Imaging, Rudolfinerhaus Hospital. Subjects: Twelve healthy volunteers. Interventions: Volunteers were imaged, using a multislice-multiphase technique during spontaneous breathing and with PEEP values of O, 7, and 15 cm H2O. Measurements and Main Results: Atrial as well as ventricular volumes, chest diameters, and midventricular contact between the heart and anterior chest wall were determined on transverse-oblique sections. Atrial volumes showed a progressive decline beginning at a PEEP of 7 cm H2O. Diastolic filling of both ventricles was reduced. A PEEP level of 15 cm H2O induced a significant increase in the sagittal-oblique but not in the transverse-oblique chest diameter. PEEP values of 7 and 15 cm H2O shortened the length of the midventricular contact between the heart and anterior chest wall. Conclusions: Left and right ventricular end-diastolic volumes and stroke volumes decreased significantly during ventilation with PEEP at 15 cm H2O, as did end-systolic atrial volumes. Volume changes in association with changes of chest and heart configuration suggest external cardiac compression by the expanding lungs. Furthermore, this study illustrates the feasibility of magnetic resonance imaging in mechanically ventilated patients.