Estimating left ventricular contractility using inspiratory-hold maneuvers.

OBJECTIVE: To compare estimates of left ventricular (LV) end-systolic elastance created by inferior vena caval (IVC) occlusion with those by apneic continuous positive airway pressure (CPAP). DESIGN AND
SETTING: Prospective interventional study in a university large animal research laboratory.
SUBJECTS: Sixteen intact, pentobarbital-anesthetized mongrel male dogs.
INTERVENTIONS: Insertion of LV conductance and pressure catheters, then during apnea sequentially performed IVC occlusion and CPAP of 5, 10, and 15 mmHg for 10 s, each interspersed by positive-pressure breathing. In the final 11 dogs runs were repeated during both esmolol (2 mg min-1) and dobutamine (5 microg kg-1 min-1) infusions. MEASUREMENTS: LV pressure-volume relationships during apneic baseline and then as LV end-diastolic volume decreased by each maneuver to calculate LV end-systolic elastance and preload-recruitable stroke work as measures of contractility.
RESULTS: End-systolic elastance estimated at 5 mmHg CPAP levels and IVC occlusions were similar while 10 and 15 mmHg CPAP gave different values. However, end-systolic elastance was lower during esmolol infusion and higher during dobutamine for all CPAP and IVC occlusion maneuvers. Preload-recruitable stroke work measures were similar across maneuvers. With increasing CPAP the LV filling and end-systolic elastance were progressively shifted upward and to the left, with volume on the x-axis, consistent with an unaccounted for increase in intrathoracic pressure.
CONCLUSIONS: The use of 5 mmHg CPAP-induced preload-reduction allows estimation of LV end-systolic elastance and preload-recruitable stroke work in intact dogs. Increasing CPAP to more than 10 mmHg creates estimates of LV contractility that are different but covary with IVC occlusion-derived values.