Dimensional analysis of right and left ventricles during positive-pressure ventilation in dogs

Our purpose was to determine the effects of controlled ventilation with positive end-expired pressure (PEEP) on ventricular dimensions and to relate changes in shape to changes in stroke volume and left ventricular volumes. Left and right ventricular dimensions were measured using biplane cinefluorography of dogs with radiopaque markers implanted in their hearts, and left ventricular volumes were derived from left ventricular dimensions by assuming that the left ventricle conformed to the shape of a nonprolate ellipsoid. As PEEP increased from 0 to 5, 10, and 15 cmH₂O, stroke volume fell 36%, and all three left ventricular end-diastolic dimensions fell, with apex-base falling 5%, anterior-posterior falling 7%, and septal-lateral falling nearly twice as much, 12%. This resulted in a 11.3 cm³ fall in left ventricular end-diastolic volume. The right ventricular end-diastolic dimensions changed in opposite directions with respect to each other as the level and PEEP was raised to 15 cmH₂O; one axis fell 3.2 mm, and the midpoint of the right ventricular free wall moved outward by 1.7 mm. Thus the fall in cardiac output (and stroke volume) during PEEP was associated with a fall in left ventricular configurations. It is not known whether the left ventricular septal-lateral narrowing is the consequence of lateral wall compression by the lungs or encroachment on the left ventricle by the septum.