Circulation, Vol 89, 810-817, Copyright © 1994 by American Heart Association
T Nozawa, CP Cheng, T Noda and WC Little
BACKGROUND: The relation between left ventricular (LV) oxygen consumption
(MVO2) and pressure-volume area (PVA) developed in isolated hearts provides
a powerful method to understand cardiac energetics. We investigated
application of this relation to the intact circulation, determining its
response to steady-state and transient load alterations and enhanced
contractility in conscious animals. METHODS AND RESULTS: Eight dogs were
instrumented to measure LV pressure (micromanometer), LV volume (three
sonomicrometers), and left circumflex and anterior descending coronary
artery flows (ultrasonic flowmeter). Data were acquired after recovery from
the surgery with the animals awake and unsedated. After administration of
hexamethonium and atropine, steady- state loading conditions were changed
with phenylephrine or nitroprusside in four to five steps before and during
the infusion of dobutamine (6 to 10 micrograms.-1kg.-1min). MVO2 and PVA
obtained under steady-state conditions were linearly correlated both before
and during dobutamine. The MVO2-PVA relation obtained on a beat-to-beat
basis during transient caval occlusion was less linear and not coincident
with the steady-state relation. Dobutamine shifted the steady-state
MVO2-PVA relation upward in all hearts, increasing the MVO2 axis intercept
of the MVO2-PVA relation (P < .01). This intercept correlated with
ventricular contractility assessed by the slope (Ees) of the LV
end-systolic pressure-volume relation determined by caval occlusion (r =
.76, P < .05). The slope of the MVO2-PVA relation increased with
dobutamine in seven of eight animals, with the inverse of the slope
(representing contractile efficiency) being 31 +/- 6% during control and 24
+/- 6% after dobutamine (P = .06). CONCLUSIONS: MVO2 and PVA are linearly
related during steady-state alterations in loading conditions in conscious
dogs but not on a beat-by-beat basis during transient caval occlusion.
Increase in contractility by dobutamine produces an upward shift of the
MVO2-PVA relation.
ARTICLES
Relation between left ventricular oxygen consumption and pressure- volume area in conscious dogs
Section of Cardiology, Bowman Gray School of Medicine, Wake Forest University, Winston-Salem, NC 27157-1045.
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