title: Timing and velocity of ejection as major determinants of end-systolic pressure in isolated rabbit hearts.
abstract: BACKGROUND
  Systolic shortening is known to produce muscle deactivation. The present study was designed to analyze whether the velocity and the timing of ejection play a role on end-systolic pressure-volume relations (ESPVR).
  
  
  RESULTS
  In isolated rabbit hearts, left ventricular pressure and volume were recorded and digitized, and left ventricular volume was controlled by a servosystem (4-millisecond cycles) to alter the timing of ejection. A significant deficit in end-systolic pressure was observed when ejection was late in systole with respect to earlier ejection. This was associated with a significantly reduced end-systolic elastance. End-systolic pressure of beats with slow ejection was intermediate between that of the beats with early ejection and that of beats with late ejection with a significantly increased end-systolic volume compared with beats with early rapid ejection. The same results were obtained with hypertrophied hearts (abdominal aortic stenosis). Pressure-volume loop areas were significantly increased in beats with slow ejections and with rapid delayed ejections versus early rapid ejections. No change in the positive peak of dP/dt was observed when the timing and the velocity of ejection were modified.
  
  
  CONCLUSIONS
  ESPVR is modified by the ejection profile, with a decreased end-systolic pressure and an increased pressure-volume loop area related to the velocity and the amount of shortening during the end-systolic phase. These indices of ventricular function thus must be used with caution when the timing of ejection is altered, and the end-diastolic volume-peak dP/dt relation may be a better index of ventricular function.
authors.affiliation: Unité INSERM U400, Faculté de Médecine, Créteil, France.
authors.forename: A
authors.initials: A
authors.lastname: Ezzaher
authors.forename: T
authors.initials: T
authors.lastname: el Ouazzani
authors.forename: B
authors.initials: B
authors.lastname: Crozatier
mesh_terms: D000818:Animals; D001794:Blood Pressure; D001810:Blood Volume; D006332:Cardiomegaly / Q000503:physiopathology; D006321:Heart / Q000502:physiology*; D066298:In Vitro Techniques; D009200:Myocardial Contraction; D011817:Rabbits; D012016:Reference Values; D013599:Systole; D013997:Time Factors; D016277:Ventricular Function, Left