The effects of mechanical changes in loading conditions on the left ventricular end-systolic pressure-volume relation (ESPVR) were studied in nine open-chest dogs, including three dogs studied before and after f3-adrenergic blockade. Left ventricular pressure was measured with a micromanometer, and left ventricular volume was measured with a conductance catheter. ESPVRs were obtained by increasing left atrial inflow over wide volume ranges (as much as threefold) under three different conditions: control or high or low aortic impedance. High impedance was obtained by occlusion of the descending aorta, and low impedance was obtained by a shunt between the subclavian artery and the left atrium. In the unblocked animals in 21 of 28 runs, a second-order polynomial equation gave a better fit for the ESPVR than a linear relation. To quantify the effects of the changes in aortic impedance on the ESPVR, we calculated from the quadratic equation its volume intercept (V18) and its local slope (E18) at an end-systolic pressure (Pes) of 18 kPa. In the unblocked animals, a statistically significant difference was found in V18 between low impedance (21.50+6.27 ml) and high impedance (14.10±8.98 ml; p<0.005) and between control (19.14+±9.58 ml) and high impedance (p<0.05). In most dogs, E18 was increased at high and decreased at low impedance, but not significantly. In the additional experiments with P-blockade, the nonlinearity diminished somewhat, but the load dependency of the ESPVR remained present after P-blockade because the same leftward shift of the ESPVR with high aortic impedance was found. Two other relations, namely, of dP/dtmaX and of stroke work versus end-diastolic volume, were also investigated, which on the whole showed the same behavior as the ESPVR. These results indicate that the ESPVR and dP/dtmax-Ved and stroke work-end-diastolic volume relations, when studied over a wide volume range, are nonlinear and that changes in loading conditions influence indexes of contractility derived from these relations, especially the volume intercepts, in such a way that an increase in aortic impedance may be interpreted as an increase in contractility. Blocking the f3-adrenergic receptors did not influence the load dependency of the ESPVR but, in some cases, tended to decrease the nonlinearity in concordance with the relation between contractility and nonlinearity in isolated hearts. (Circulation 1991;83:315-327) The applicability of the end-systolic pressurevolume relation (ESPVR) to studying the contractile performance of the left ventricle is dependent on the shape of the relation and on its sensitivity to changes in loading conditions of the
The effect of an on-line manometer on the variables of ventilation i.e. peak inspiratory pressure (PIP), mean airway pressure (MAP), positive end expiratory pressure (PEEP), and inspiratory to expiratory time ratio (I:E) was studied in vitro. Analysis of PIP, MAP, PEEP, and I:E was made during hand ventilation of a resuscitation mannequin at the preselected PIP of 15 and 25 cm water with and without a manometer. Use of the manometer decreased the range of variation in PIP, but the MAP was higher. This was due to an increased I:E while PEEP remained unchanged. An on-line manometer during hand ventilation prevents excessive PIP but may increase the MAP and therefore may not prevent development of a pneumothorax.
EI appears to be a safe and feasible method for decreasing preterm contractions. To confirm and test effectiveness, longer interventions and additional cases are needed.
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