title: Direct compression of the failing heart reestablishes maximal mechanical efficiency.
abstract: BACKGROUND
  In failing hearts, homeostatic mechanisms contrive to maximize stroke work and maintain normal arterial blood pressure at the expense of energetic efficiency. In contrast dobutamine reestablishes maximal mechanical efficiency by promoting energetically optimal loading conditions. However, dobutamine also wastefully increases nonmechanical oxygen consumption. We investigated whether direct mechanical cardiac compression would reestablish maximal mechanical efficiency without the oxygen-wasting effect.
  
  
  METHODS
  The pressure-volume relationship and myocardial oxygen consumption were derived in sheep using left ventricular pressure and volume from manometer-tipped and conductance catheters, and coronary flow from Transonics flow probe.
  
  
  RESULTS
  Propranolol hydrochloride and atropine sulfate were administered to reduce ejection fraction to 21% when ventricular elastance fell to 1.35 mm Hg/mL and mechanical efficiency to 79% of maximal. Low-pressure direct mechanical compression of the failing heart restored mechanical efficiency to 94% of maximal and realigned optimal left ventricular end-systolic pressure with operating left ventricular end-systolic pressure without altering nonmechanical oxygen consumption.
  
  
  CONCLUSIONS
  We conclude that direct cardiac compression restores mechanical efficiency to normal maximum without wasting energy on additional nonmechanical activity.
authors.affiliation: Cooperative Research Centre for Cardiac Technology, Department of Cardiology, Royal North Shore Hospital, St. Leonards, Sydney, Australia.
authors.forename: Russell A J
authors.initials: RA
authors.lastname: Carrington
authors.forename: Yifei
authors.initials: Y
authors.lastname: Huang
authors.forename: Osamu
authors.initials: O
authors.lastname: Kawaguchi
authors.forename: Takeshi
authors.initials: T
authors.lastname: Yuasa
authors.forename: Kazuaki
authors.initials: K
authors.lastname: Shirota
authors.forename: Donald
authors.initials: D
authors.lastname: Martin
authors.forename: Stephen N
authors.initials: SN
authors.lastname: Hunyor
mesh_terms: D000818:Animals; D001794:Blood Pressure / Q000502:physiology; D006321:Heart / Q000502:physiology*; D006353:Heart-Assist Devices; D008955:Models, Cardiovascular; D008962:Models, Theoretical; D010101:Oxygen Consumption / Q000502:physiology; D011312:Pressure; D012756:Sheep; D013396:Suction