Estimation of left ventricular elastance without altering preload or afterload in the conscious dog.
OBJECTIVE
The aim was to determine the slope (EES) of the left ventricular end systolic pressure-volume line (ESPVL) without altering preload or afterload in conscious dogs.


METHODS
Dogs (n = 10) were instrumented to determine left ventricular volume from ultrasonic left ventricular internal dimensions, and to measure left ventricular pressure using a micromanometer. Studies were performed one to two weeks after instrumentation while the animals were conscious. ESPVL was determined from variably loaded left ventricular pressure-volume (P-V) loops generated by the vena caval occlusion. Contractile state was increased by intravenous dobutamine (8 micrograms.kg-1 x min-1) and decreased by intravenous verapamil (10 mg) given after autonomic blockade. From a single normally ejecting beat, we calculated EES-single beat (mm Hg.ml-1) as peak isovolumetric pressure (Pmax) minus end systolic pressure divided by stroke volume. Sunagawa's technique was used to estimate Pmax by fitting the pressure during the isovolumetric contraction and relaxation as: P(t) = 1/2 X Piso[1-cos(omega t+c)]+LVEDP, where Piso = peak isovolumetric developed pressure, LVEDP = left ventricular end diastolic pressure, c = constant accounting for variations in phase angle, and omega = 2 pi/T in which T is duration of contraction.


RESULTS
After dobutamine, EES increased, from 8.9(SEM 0.8) to 12.5(1.0) mm Hg.ml-1 (p < 0.05), and EES-single beat increased from 9.1(0.9) to 12.0(1.4) mm Hg.ml-1 (p < 0.05). Conversely, after verapamil, EES decreased, from 11.1(1.2) to 6.3(1.1) mm Hg.ml-1, (p < 0.05), and EES-single beat also decreased, from 9.6(1.0) to 7.3(1.2) mm Hg.ml-1, (p < 0.05).


CONCLUSIONS
EES calculated from one beat is similar to EES determined from variably loaded left ventricular loops and responds appropriately to inotropic stimulation. This technique provides a reasonable method to calculate EES from left ventricular pressure and stroke volume without altering preload or afterload.
Nakamoto
T
T
Section of Cardiology, Bowman Gray School of Medicine, Wake Forest University, Winston-Salem, North Carolina.
Cheng
C P
CP
Santamore
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WP
Iizuka
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M
D000818:Animals; D001364:Awareness / Q000502:physiology; D004280:Dobutamine / Q000494:pharmacology; D004285:Dogs; D004452:Echocardiography; D006439:Hemodynamics / Q000187:drug effects; D008365:Manometry; D009200:Myocardial Contraction / Q000502:physiology; D015203:Reproducibility of Results; D013318:Stroke Volume / Q000502:physiology; D016277:Ventricular Function, Left / Q000502:physiology*; D014700:Verapamil / Q000494:pharmacology
D004280:Dobutamine; D014700:Verapamil