Effect of negative intrathoracic pressure on left ventricular pressure dynamics and relaxation

To investigate the effect of a fall of intrathoracic pressure on left ventricular (LV) hemodynamics and relaxation, simultaneous micromanometric recordings of LV and aortic pressures were performed at rest and during two graded Mueller maneuvers in 16 patients undergoing cardiac catheterization for aortic valve stenosis (n = 8) or chest pain (n = 8). The reductions (means +/- SE) of airway pressure during the lesser and greater maneuvers were 26 +/- 1 and 42 +/- 1 mmHg, respectively. Simultaneously, LV isovolumic-developed pressure increased by 9 +/- 3 and 21 +/- 4 mmHg, respectively (P < 0.03 for both). During the greater maneuver, the individual changes of the time constant of LV isovolumic relaxation (tau) correlated with the changes of LV isovolumic-developed pressure (r = 0.73; P = 0.002). In patients with a > 20-mmHg rise in isovolumic-developed pressure, tau increased by 10.3 +/- 4.6 ms. By multiple-regression analysis, the change of tau was related directly to the change of isovolumic-developed pressure (standardized coefficient beta = 0.80; P = 0.001) and inversely related to the resting systolic LV-aortic pressure gradient (beta = -0.37; P = 0.050). The other hemodynamic changes were independent of aortic valve stenosis. In conclusion, during the Mueller maneuver, the LV isovolumic contraction load increases and tau lengthens, particularly with higher elevations of LV systolic load.