title: Estimating left ventricular contractility using inspiratory-hold maneuvers.
abstract: 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).
  
  
  METHODS
  Prospective interventional study in a university large animal research laboratory.
  
  
  METHODS
  Sixteen intact, pentobarbital-anesthetized mongrel male dogs.
  
  
  METHODS
  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.
  
  
  METHODS
  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.
authors.affiliation: Cardiopulmonary Research Laboratory, Department of Critical Care Medicine, School of Medicine, University of Pittsburgh, 3550 Terrace Street, Pittsburgh, PA 15261, USA.
authors.forename: Hyung Kook
authors.initials: HK
authors.lastname: Kim
authors.forename: Mohammed T
authors.initials: MT
authors.lastname: Alhammouri
authors.forename: Yasser M
authors.initials: YM
authors.lastname: Mokhtar
authors.forename: Michael R
authors.initials: MR
authors.lastname: Pinsky
mesh_terms: D000818:Animals; D045422:Continuous Positive Airway Pressure; D004285:Dogs; D006334:Heart Function Tests / Q000379:methods*; D001239:Inhalation; D009200:Myocardial Contraction / Q000502:physiology*; D016276:Ventricular Function