title: Continuous-flow cardiac assistance: effects on aortic valve function in a mock loop.
abstract: BACKGROUND
  As the use of left ventricular assist devices (LVADs) to treat end-stage heart failure has become more widespread, leaflet fusion--with resul-tant aortic regurgitation--has been observed more frequently. To quantitatively assess the effects of nonpulsatile flow on aortic valve function, we tested a continuous-flow LVAD in a mock circulatory system (MCS) with an interposed valve.
  
  
  METHODS
  To mimic the hemodynamic characteristics of LVAD patients, we utilized an MCS in which a Jarvik 2000 LVAD was positioned at the base of a servomotor-operated piston pump (left ventricular chamber). We operated the LVAD at 8000 to 12,000 rpm, changing the speed in 1000-rpm increments. At each speed, we first varied the outflow resistance at a constant stroke volume, then varied the stroke volume at a constant outflow resistance. We measured the left ventricular pressure, aortic pressure, pump flow, and total flow, and used these values to compute the change, if any, in the aortic duty cycle (aortic valve open time) and transvalvular aortic pressure loads.
  
  
  RESULTS
  Validation of the MCS was demonstrated by the simulation of physiologic pressure and flow waveforms. At increasing LVAD speeds, the mean aortic pressure load steadily increased, while the aortic duty cycle steadily decreased. Changes were consistent for each MCS experimental setting, despite variations in stroke volume and outflow resistance.
  
  
  CONCLUSIONS
  Increased LVAD flow results in an impaired aortic valve-open time due to a pressure overload above the aortic valve. Such an overload may initiate structural changes, causing aortic leaflet fusion and/or regurgitation.
authors.affiliation: Center for Cardiac Support and the Cardiovascular Research Laboratories, Texas Heart Institute at St. Luke's Episcopal Hospital, Houston, Texas 77030, USA. etuzun@heart.thi.tmc.edu
authors.forename: Egemen
authors.initials: E
authors.lastname: Tuzun
authors.forename: Marcel
authors.initials: M
authors.lastname: Rutten
authors.forename: Marco
authors.initials: M
authors.lastname: Dat
authors.forename: Frans
authors.initials: F
authors.lastname: van de Vosse
authors.forename: Cihan
authors.initials: C
authors.lastname: Kadipasaoglu
authors.forename: Bas
authors.initials: B
authors.lastname: de Mol
mesh_terms: D001021:Aortic Valve / Q000502:physiology*; D001022:Aortic Valve Insufficiency / Q000209:etiology / Q000503:physiopathology*; D006353:Heart-Assist Devices / Q000009:adverse effects*; D006439:Hemodynamics / Q000502:physiology*; D006801:Humans; D008953:Models, Anatomic; D010477:Perfusion / Q000379:methods; D013318:Stroke Volume / Q000502:physiology; D017725:Ventricular Pressure / Q000502:physiology