Effect of the Mueller manoeuvre at different lung volumes on left ventricular performance in normal subjects.
The effect of reduced intrathoracic pressure at different lung volumes on cardiac function was assessed by echocardiographic measurements of left ventricular size in normal subjects who performed the Mueller manoeuvre at two preselected lung volumes. At functional residual capacity (FRC), both mean end-diastolic dimension and mean end-systolic dimension increased (5.1 +/- 0.4 to 5.4 +/- 0.5 cm; P less than 0.001 and 3.7 +/- 0.4 to 3.9 +/- 0.4 cm; P less than 0.025, respectively). At high lung volume (HLV), midway between FRC and total lung volume, mean end-diastolic dimension increased from 5.1 +/- 0.5 to 5.3 +/- 0.5 cm (P less than 0.001), less than than the increase at FRC, and mean end-systolic dimension increased from 3.5 +/- 0.4 to 3.9 +/- 0.4 cm (P less than 0.001), similar to the increase at FRC. Thus, mean stroke dimension and shortening fraction were reduced at HLV (1.5 +/- 0.2 to 1.3 +/- 0.2 cm and 30 +/- 4 to 26 +/- 2% respectively, P less than 0.025). At FRC and HLV respectively, mean left ventricular transmural pressure increased from 111 to 129 Torr (P less than 0.001) and from 111 to 128 Torr (P less than 0.001) in response to the Mueller manoeuvre, although intraesophageal (intrathoracic) pressure was significantly lower (P less than 0.001) during the Mueller manoeuvre at HLV. These results show that lung volume affects the left ventricular response to the Mueller manoeuvre. Furthermore, the changes in left ventricular dimensions induced by the Mueller manoeuvre are determined by the level of reduced intrathoracic pressure, through differing effects on left ventricular afterload and filling.