Leftward septal displacement during right ventricular loading in man.

Little direct evidence in man indicates that acute right ventricular loading alters left ventricular configuration. We used the Mueller maneuver (forced inspiration against a closed airway) to increase right ventricular loading and evaluated septal shape and right and left ventricular size in nine normal, semisupine men with phased-array, two-dimensional echocardiography. End-systolic and end-diastolic frames in cross-sectional and longitudinal views of the ventricles were recorded at rest and at various phases during the Mueller period (peak inspiratory effort of 40-60 mm Hg negative pressure). Acute leftward displacement of the septum at end-diastole on cross section during the maximal early Mueller period (first two or three beats after the onset of Mueller maneuver) was evidenced by a substantial increase in the radius of curvature of the septal segment (3.72 0.25 cm vs control, 2.49 0.12 cm,p < 0.001). This leftward septal displacement per- sisted not only during end-diastole, but also during end-systole (3.58 0.45 vs 2.04 0.16 cm;p < 0.01). The septal radius of curvature did not differ from the radius of curvature of the remainder of the left ventricle at rest for systole or diastole (1.94 0.11 and 2.48 0.09 cm, respectively), but differed markedly during the early Mueller phase in both systole (3.58 + 0.45 vs 1.9 0.07 cm; p < 0.005) and diastole (3.72 0.25 vs 2.36 0.07 cm; p < 0.001). Simultaneously, left ventricular end-diastolic cavity areas decreased from control to the early Mueller phase on cross-sectional view from 19.14 1.08 cm2 to 15.73 0.65 cm2 (p < 0.005), and longitudinal view from 29.83 2.08 to 20.74 1.46 cm2; p < 0.001. A significant decrease in end- systolic cavity area was also noted in this view (19.72 i 2.0 to 15.23 1.98 cm2;p < 0.05). Right ventricular end-diastolic diameter increased from control to the early Mueller phase in the cross-sectional view (1.06 0.14 to 1.31 0.17 cm;p < 0.02), as well as in the longitudinal view (1.14 0.23 to 1.80 0.43 cm; p < 0.05). A decrease in left ventricular volume with maintenance of constant shape should result in a shortened radius of curvature for all portions of the ventricle, so the increase in septal radius of curvature in the face of an overall decrease in left ventricular size indicates that right ventricular loading alters left ventricular shape by flattening the septum. This septal flattening persists during systole. Thus, changed septal shape may be an important mechanism of, and evidence for, ventricular interdependence in normal man.